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You check the clock and realize you're running late. The school bus is going to arrive any minute now. You grab your backpack and head for the door, but you're stopped by a parent's voice reminding you to grab your coat and an umbrella.

What's the deal? You look out the door, and it doesn't look cold or rainy. Before you can even protest, you're told that the temperature is going to drop when it begins to rain later this afternoon. Can your parents see into the ? Do they have a crystal ball? Not likely! They probably just checked the weather forecast.

Weather forecasts help us prepare for the , whether it's a few hours from now or the rest of the week. Not only do they warn us of potentially -dangerous weather headed our way, they also give us an of what to expect in terms of temperature and chance of precipitation , so we can dress and ourselves appropriately.

The people who study the weather and put together forecasts are scientists known as meteorologists. Have you ever seen a forecast that called for lots of snow? You might have gotten excited, anticipating a snow day and the chance to do some sledding. Unfortunately, you woke up to clear skies, no snow, and a full day of school ahead. What happened? How could the weather forecast have been so wrong?

Weather forecasting is not a perfect science. Forecasts are a prediction based upon an educated . Since there are a wide variety of factors that go into a forecast, it's possible for meteorologists to wrong from time to time. Fortunately, modern technology has allowed forecasters to become much more over the last decade.

Today, meteorologists use complicated mathematical equations to help predict the weather as part of a process known as numerical forecasting. Numerical forecasting requires powerful supercomputers and tons of observational from land, sea, and air weather stations around the world.

Where does all this come from? Sometimes it comes from regular people like you! Many people create their own backyard weather stations with thermometers to measure temperature and rain gauges to measure precipitation . They can report their observations to meteorologists to help improve forecasts.

Technologically-advanced weather stations are established by meteorologists all over the world. They collect and share to help improve forecasts. Some of the tools they use include barometers that measure air pressure, anemometers that measure wind speed, Doppler stations to monitor the movement of weather fronts, and psychrometers to measure relative humidity.

To get from the seas and the upper atmosphere, -collection tools and instruments may be attached to ships, airplanes, and even buoys in the middle of the ocean. Weather balloons and weather satellites also provide observational that can be used on a global scale to spot weather trends for large areas.

All these different types of tools around the world produce millions of pieces of weather-related observational every single day. Supercomputers, such as those at the National Centers for Environmental Prediction in Camp Springs, Maryland, process that to produce forecasts based upon complicated mathematical models. Current is compared to similar patterns that have occurred in the past to determine what will likely happen in the .

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We predict today's Wonder of the Day will contain mostly-sunny smiles with a 100% chance of WONDER!

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Why Do Different States Have Different Weather?

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Why Do Different States Have Different Weather?

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If you have ever taken a long trip, you may have noticed the can be quite different in different parts of the country. For example, if you travel from Detroit to Miami in December, you may need a large suitcase.

The and ice of a Detroit winter may mean you wear boots and a onto the plane, but by the you get to Miami, you will be ready for a swimsuit and shorts! The reason for the difference in is that Detroit and Miami have very different climates.

Many factors, such as elevation, ocean currents, distance from the sea, and prevailing winds, can affect the of an area. One of the most important things that influences , though, is . The of an area indicates how far it is - north or south - of the equator.

affects because it is related to the length and intensity of sunlight an area receives. As Earth orbits the sun, sometimes the Northern Hemisphere is tipped toward the Sun, while at other times the Southern Hemisphere is tipped toward the Sun.

When a is closer to the Sun, its days are longer, and the Sun's rays are stronger and more direct. When our hemisphere is tipped toward the Sun, we experience warmer and longer days. This is our summer. When we tip away from the Sun, the days are shorter and colder. This is winter.

But none of this explains why Detroit and Miami would have such different on the same day in the same month, does it? Actually... it does!

Miami is much closer to the equator than Detroit. This means the tipping of the hemispheres has less extreme effects on Miami than Detroit. Because Miami is closer to the equator, it receives a lot of sunlight and warmth all year long and thus maintains a warm .

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Why Do Different States Have Different Weather?

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If you have ever taken a long trip, you may have noticed the can be quite different in different parts of the country. For example, if you travel from Detroit to Miami in December, you may need a large suitcase.

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Is it going to be a winter? Or will it be ? How can you tell?

Do you on the almanac? Or do you turn to woolly worms?

For many, many years, has held that woolly worms can whether the coming winter will be or . Is there any to this ? Or is it an old wives' tale?

Woolly worms are actually the stage of the Isabella tiger moth ( Pyrrharctia Isabella). They are known by various names, including woolly bear caterpillars, woolly bears, fuzzy bears, and black-ended bears.

Woolly worms get their name from their fuzzy appearance . They have black bands at each end with a red-brown band in the middle.

Each , woolly bear caterpillars take shelter under leaves and other low-lying vegetation . In the spring, they complete their transformation into Isabella tiger moths.

People who believe woolly worms can the weather think that a narrow red-brown band means a winter. The wider the red-brown band is, the milder the coming winter is supposed to be.

There are several towns in the United States that hold annual woolly worm each fall. In addition to caterpillar races, these also usually feature an official declaration of the woolly worm's prediction for the coming winter.

But how are woolly worms at predicting the weather? As it turns out, they're not so .

Scientists who have tested woolly worms' predictions have found that there is no correlation between woolly worms' bands and winter weather. Instead, they note that the color and size of a woolly worm's bands are likely affected by several factors, including availability of food, conditions during development, age, and species.

Woolly worms aren't the only creatures that people look to for information about the weather, though. Here are some of the other animals and insects that people believe have weather-predicting abilities:

Groundhogs: Each February 2, Americans wait for groundhog Punxsutawney Phil to whether we will have six more weeks of winter or an early spring. Unfortunately, the National Climatic Data Center claims that Phil has only correctly predicted the weather about 39 percent of the time.

Frogs: Some people believe that frogs croak louder and longer than normal when bad weather is on the way.

Birds: How high are the birds in the sky? This is the question some people ask themselves. They believe that high-flying birds signal clear weather, and low-flying birds mean a storm is headed your way.

Bees: If you notice that the bees buzzing around your flowers have suddenly gone missing, you can bet that bad weather may be on the way.

Ladybugs: As the old saying goes, "When the ladybugs swarm, expect a day that's warm." On the other hand, if they're looking for shelter, cold weather is on its way.

Ants: If you notice ants building up their mounds for extra protection or even covering the mounds' holes, you might want to prepare for some rain!

Can all of these animals and insects successfully the weather? Not always!

However, scientists do believe that many animals and insects have heightened senses that allow them to when certain types of weather are imminent. Confirm with the weatherman , but pay attention when you see animals and insects behaving in strange ways!

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Is it going to be a winter? Or will it be ? How can you tell? Do you on the almanac? Or do you turn to woolly worms? For many, many years, has held that woolly worms can whether the coming winter will be or . Is there any to this ?

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Pour a glass of and take a sip. Pretty good, isn't it? Would you believe the you're drinking has been around for millions of years? It's true!

Before any creatures were living on land, your was part of the . The we have on Earth has been here for a very, very long time, and Mother has been constantly recycling it through the .

Once is in the , it rises into the atmosphere , cools, and forms clouds through a process called condensation . If you have ever poured a cool glass of lemonade on a hot day, you have probably seen condensation in action.

The next step in the - precipitation - occurs when so much has condensed that the can no longer hold it. Clouds become heavier and heavier until eventually the falls back to the Earth in the form of precipitation . Depending on atmospheric conditions and temperatures, precipitation can arrive on Earth as , hail, sleet, freezing , or snow.

When falls back to Earth as precipitation , it ends up in rivers, lakes, oceans, swimming pools, barrels, bird baths, and lots of other places. This final step of the is called collection .

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Pour a glass of and take a sip. Pretty good, isn't it? Would you believe the you're drinking has been around for millions of years? It's true! Before any creatures were living on land, your was part of the .

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, , go away. Come again some other day. That's how we feel sometimes when all we want to do is go outside and play.

However, plays an important role in our world. It replenishes the Earth with water and helps our plants grow. Without regular rainfall, our world would be a dry, dusty place that wouldn't be any fun at all.

If you see clouds roll in on a sunny day, it could mean that is on the way. Have you ever stared at those clouds and wondered whether they hold and, if so, how much?

As it turns out, that question isn't easy to answer. Why? Clouds aren't like buckets, so they don't really "hold" water like a bucket would.

Whether you realize it or not, the air around you is filled with water. Water comes in three forms: liquid (that you drink), solid (ice) and gas (water in the air). The amount of water inside a is no different than the amount of water in the air around it.

In the air around a , water is a gas in the form of water . Inside the , cooler temperatures have transformed water into a liquid. This liquid is in the form of millions, billions or even trillions of tiny water droplets called droplets. Scientists call this process condensation .

When water in the air condenses into tiny droplets, those droplets become visible. What we see is a . Whether that liquid water will fall to the ground as depends on many factors.

droplets are very tiny and weigh very little. In a , they float with the wind or simply hang in the air. In addition, updrafts (winds that blow upward from the surface of the Earth) also help keep droplets suspended within a .

To fall to Earth, droplets have to become heavier. If they combine with other droplets or if more liquid water continues to condense out of the air, they eventually become heavy enough to form drops that fall to Earth as . The scientific word for rainfall is precipitation .

Once droplets grow into drops and fall to Earth as , it will continue to as long as conditions in the atmosphere keep causing water to condense into liquid water and grow into drops heavy enough to fall as .

So how much can a produce? This is perhaps a better question than how much a can hold. Scientists estimate that one inch of falling over an area of one square mile is equal to 17.4 million gallons of water. That much water would weigh 143 million pounds!

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go away. Come again some other day. That's how we feel sometimes when all we want to do is go outside and play. However, plays an important role in our world. It replenishes the Earth with water and helps our plants grow.

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Do you love windy days? The answer to that question probably depends upon where you are and what kind of weather you're experiencing. If you're on a tropical beach on a hot, sunny day, then a cool ocean breeze probably feels fantastic.

However, if you're walking several blocks to school on a winter morning, then a bone- breeze probably isn't welcome at all. On those days, the just makes you even colder than you already are.

If you spend much time outdoors, you already know that the comes and goes. But where does it come from? And where does it go? When it's windy, is there a giant creature in the sky blowing air your way? Is there a huge cosmic fan trying to cool you down?

Fear not! There aren't any fans or interstellar monsters creating and sending your way. is actually a simple matter of science, and it's caused by something way out in space that you're very familiar with: the Sun!

Does that seem kind of odd to you? After all, usually cools you off. How is it that the star that heats our planet is also responsible for those cooling winds? Let's take a closer look at how winds come about.

At its most basic, is simply masses of air molecules moving very quickly. The air you breathe is made up of a variety of molecules. (78%) and oxygen (21%) make up most of the air you breathe. In addition to these two elements, there is also water and a mixture of other elements.

At every moment of every day, you're surrounded by trillions upon trillions of air molecules that are moving around and colliding with each other, you, and everything else. As these air molecules bounce into and off of you, they exert a force on you that scientists call air pressure.

Scientists define air pressure as the amount of force the air molecules exert on any given area. As a general rule, the more air molecules there are, the greater the air pressure will be. Air pressure is not constant, because it varies as a result of different factors, especially temperature. These differences in air pressure are what give to .

So how does this relate to the Sun? The Sun heats Earth's surface every single day, but it doesn't do so . Earth's surface is made up of different substances at differing elevations. As a result, the air above it will be unevenly heated by the Sun. For example, the air above land heats up faster than the air above oceans and lakes.

These different air masses will have different air pressures. As air above land heats up, it expands and rises higher into the atmosphere , creating an area of lower pressure in its . The air above a nearby ocean, on the other hand, will be cooler and heavier, in higher air pressure.

As the warm air above land rises, the cooler air over the water will move quickly to fill the space left by the rising warm air. These quickly-moving air molecules are what we know as ! In general, air molecules will tend to move more quickly and create as they move from an area of high pressure to an area of lower pressure.

The differences in air pressure that cause most winds are small. For example, winds on a spring day might be the result of a difference in air pressures of about 1% across several states. When air pressure differences are much greater (10%, for example) over a very small area, dangerous winds can form, such as those in a tornado.

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Do you love windy days? The answer to that question probably depends upon where you are and what kind of weather you're experiencing. If you're on a tropical beach on a hot, sunny day, then a cool ocean breeze probably feels fantastic.

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Have you ever watched a worm move? They don't move very fast, do they? Unless they're in the of a bird - a place no worm wants to be! - they don't fly south for the winter. It's also highly unlikely that they drive or take the bus. So where do they go in the winter?

If you're a visitor of Wonderopolis, you probably already know that earthworms are good for gardens. But gardens don't grow year-round. So what do earthworms do with their time in the winter when they're not gardening?

The answers to these questions depend in part on what type of worm you're talking about. There are a lot of different types of worms. Would you believe there are over 4,400 different of worms around the world? It's true!

Of those thousands of types of worms, over 2,700 of them are of earthworms. Only a of those can be found in the United States. Still, American gardens are called home by at least 30 different types of earthworms.

Some earthworms choose to live their whole lives in the ground's upper layer of soil and leaves. These earthworms never deep into the soil, so cold winter temperatures kill them.

To keep their alive, however, they lay eggs in tiny sacks that protect the eggs from freezing or drying out during the winter. In the spring, the eggs hatch and a whole new group of worms is born to repeat the life cycle.

Other earthworms, such as the night crawlers often used as fish bait, live close to the surface in warm weather and down deep in cold weather. When winter hits, these worms down below the frost line.

The frost line - sometimes called frost depth or freezing depth - is the depth at which the groundwater in soil usually freezes in winter. The frost line varies based upon conditions. It can usually be estimated based upon . The farther north you travel, the deeper the frost line.

In the United States, the frost line ranges from zero feet (in warm areas like Florida) to six feet or more (in cold areas like Alaska). To survive freezing cold temperatures , worms must to an area below the frost line wherever they live.

Night crawlers, for example, can to depths of six feet or more. When they down below the frost line, they nest in small chambers at the bottom of the tunnels they dig. Since worms can't breathe if their skin dries out, they coat the sides of their nesting chambers with a to keep them moist through the winter.

Once worms far enough underground , the soil stays at a fairly temperature that keeps the worms warm through the winter. This warmer soil down deep acts like a warm blanket and insulates the worms from the cold.

Night crawlers don't really like some animals do in the winter. If there is a warm spell during the winter, night crawlers will occasionally come back up to the surface for a while until it gets cold again. When spring returns, worms make their way back to the surface.

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Have you ever watched a worm move? They don't move very fast, do they? Unless they're in the of a bird - a place no worm wants to be! - they don't fly south for the winter. It's also highly unlikely that they drive or take the bus.

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Isn't WONDERful? On a hot day, nothing goes down quite as well as lemonade poured over a glass full of cubes. In fact, makes so many things better. For example, we love to use to make homemade cream!

When Old Man Winter comes calling, falling temperatures can turn creeks, lakes, ponds, and even rivers into frozen rinks you can skate on. But what about the ? If you've ever been to the in the winter, you've probably noticed that it doesn't like a small might.

So does the ever ? If you've seen pictures of the North Pole or the South Pole, you know that there are caps in those places. If the freezes in those areas, why doesn't the rest of the during the winter?

The freezing point of freshwater is 0° Celsius or 32° Fahrenheit. The presence of in , though, reduces the freezing point of . The more in the , the lower the freezing point will be.

When molecules displace molecules, the freezing rate slows down. This is why is often used on icy roads to slow down freezing and make them safer to travel upon.

Another factor that affects the freezing of is its . Unlike ponds, waves move around constantly. This helps retain heat. As a result, only really cold areas, such as the North Pole or South Pole, usually get cold enough for to .

About 15% of the contains sea for at least part of the year. That might not sound like a lot, but that amounts to about 10 million square miles of sea !

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Isn't WONDERful? On a hot day, nothing goes down quite as well as lemonade poured over a glass full of cubes. In fact, makes so many things better. For example, we love to use to make homemade cream! When Old Man Winter comes calling, falling temperatures can turn creeks, lakes, ponds, and even rivers into frozen rinks you can skate on.

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Do you enjoy watching snow fall on a cold winter day? We love to sip on hot cocoa while we watch snowflakes pile up outside. Later, we'll head out to build snowmen, make snow angels, and start a snowball fight! Snowy days can be a lot of fun. Have you ever heard that no two snowflakes are exactly alike? Well, that isn't exactly true. However, the chance of finding twin snowflakes is very, very, very low.

Scientists say the chances of two snowflakes being exactly alike are about 1 in 1 million trillion. That's a one followed by 18 zeros, so it's very unlikely! Meteorologists think there are 1 trillion, trillion, trillion (a one with 36 zeros!) types of snowflakes.

A snowflake has three basic ingredients: ice , water , and dust. The ice form as water freezes on a tiny piece of dust. The dust particles come from many places. It could be from flower pollen, volcanic ash, or even meteors.

Snow forms in very cold clouds. As water droplets attach themselves to the ice , they freeze, creating an even larger ice crystal. In any crystal, line up in a pattern. In ice , water line up and form a six-sided shape called a . This is why all snowflakes are six-sided!

The temperature of the cloud determines the shape of an ice crystal. Likewise, the amount of in the cloud determines the size of the ice crystal. More will create a bigger crystal. When several ice stick together, they form a snowflake.

As snowflakes tumble through the air, and , they each take a different path to the ground. Each snowflake falls and floats through clouds with different temperatures and levels. This shapes each snowflake differently. Two snowflakes from the same cloud will have different sizes and shapes because of their different journeys to the ground.

You may never find an pair of snowflakes, but they can be grouped by similarities in their patterns. People who study snowflakes group them into shapes like stellar, fernlike, needle, and many others. The next time you're out in the snow, try to catch snowflakes to examine. But be careful! Snowflakes are delicate and melt easily.

Most fun snow activities involve pushing many snowflakes together. How else could you possibly make a snow fort? Still, seeing a single snowflake up close is worth the effort. You might just find a new shape that's never been seen before!

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Do you enjoy watching snow fall on a cold winter day? We love to sip on hot cocoa while we watch snowflakes pile up outside. Later, we'll head out to build snowmen, make snow angels, and start a snowball fight! Snowy days can be a lot of fun.

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We sure have had a lot of in Wonderopolis lately, and we've been having lots of fun, too. When the winter white stuff comes down, we like to go sledding, make cream, and play hockey with our friends. We also like to go skating and build snowmen. And with all the we've had, we've made a LOT of snowmen. In fact, the current snowman population in Wonderopolis is approximately 24,387!

So, while it is getting a little crowded in Wonderopolis, we're not worried. When the weather warms up, the snowmen numbers will . What do we mean? Read on to learn where they go...

, which is a frozen (solid) form of , melts when it gets warmer than 32º F. When the Sun shines and warms the Earth, begins to and turn into . can into the ground, where it's used to help plants grow.

If the ground is already (has enough ), the will run off (get it?) into lakes, streams, rivers, and other bodies of . When it turns into a liquid as , begins its trip through the .

The Sun gets things moving by heating on land and bodies of , causing it to change to a gas called in a process called evaporation . As , the rises high into the atmosphere , where it cools and forms clouds in a process called condensation .

When clouds get too with , the falls back to Earth in a process called precipitation . Depending upon the temperature, the can hit Earth as rain, , or . Once it's back on Earth, guess what? The whole process starts over. That's why it's called the . It just keeps going on over and over again!

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We sure have had a lot of in Wonderopolis lately, and we've been having lots of fun, too. When the winter white stuff comes down, we like to go sledding, make cream, and play hockey with our friends. We also like to go skating and build snowmen.

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When the days get short and the temperature drops, what do you look forward to? If you're like many kids, you can't wait until the day when you wake up to a fresh of white snow covering the front .

A snow day means a day filled with fights, building a snowman, and mugs of hot . Since most kids can't drive yet, they don't have to worry about bad conditions . They for lots of snow. The more, the better!

Depending upon where you live, you may get lots of snow...or none at all. Generally, the farther north you live, the more likely you are to snow. Even in the northern parts of the United States, there are certain areas known for receiving large snowfalls every year.

If you want to the amount of snow you see each year, you might want to find a home somewhere in Michigan or New York near the shores of one of the Great Lakes. In those areas, you're most likely to experience what meteorologists call lake effect snows.

Lake effect snows are exactly what they sound like. They're large snowstorms that result from the effect that the Great Lakes have on the local weather.

As large masses of cold air, usually from Canada, move south, they pass over the huge open waters of the Great Lakes. Compared to the Arctic air above, the waters of the Great Lakes are relatively warm. The larger the difference in temperature between the air and the lake waters, the greater the for snowfall.

Warm from the Great Lakes rises into the lowest level of the atmosphere . As this warm air rises, clouds form in narrow bands that can produce two to three inches of snow per hour.

Lake effect snowstorms can be difficult to predict, because they can be affected by many factors. The local and the temperature of the surrounding land and water play a role.

Wind can also affect lake effect snows. It's not uncommon for lake effect snow to fall over one area while the Sun shines over nearby areas just a mile or two away.

Lake effect snow is most often associated with the Great Lakes region of the United States. However, there are at least two other places where this phenomenon also occurs: the east of Hudson Bay in Canada and the west coasts of the islands of Honshu and Hokkaido off of Japan.

So how much snow could you get during a lake effect snowstorm? A lot! The most significant lake effect snowstorms can produce snow continuously for nearly two days straight. Accumulation rates of up to six inches per hour have been measured, with 24-hour totals reaching 76 inches or more!

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When the days get short and the temperature drops, what do you look forward to? If you're like many kids, you can't wait until the day when you wake up to a fresh of white snow covering the front . A snow day means a day filled with fights, building a snowman, and mugs of hot .

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What would you think if you heard Opal, Andrew, Katrina, Hugo, Camille, and Irene were coming to town? Who are they? Long- relatives flying in for a family ?

Not quite! In fact, they're not even people at all. They're past hurricanes! Let's find out how these super storms are born.

Each year, as summer turns to fall, hurricanes begin to appear. These large storms usually occur in the southern Atlantic , Caribbean Sea, Gulf of Mexico, or the eastern Pacific .

Sometimes people think hurricanes are like big tornadoes. They're actually quite different, though.

While a might cover a mile or two of ground, hurricanes are huge storms that can sometimes be as large as 600 miles across. If you look at a map of the United States, you'll see that a hurricane that large would stretch from Philadelphia to Indianapolis!

Tornadoes also usually last no more than a few minutes. Hurricanes, however, can last more than a week because they travel at speeds of only 10 to 20 miles per hour as they cross the .

Hurricanes are defined by their strong winds that can blow from 75 to 200 miles per hour. Before a becomes a hurricane, it starts out as a . storms have wind speeds between 39 and 74 miles per hour.

Even though these storms are not yet hurricanes, they can still cause damage and . Once a 's wind speeds reach or exceed 75 miles per hour, the becomes classified as a hurricane.

Not all storms become hurricanes. Wonder why? The key ingredient to forming a hurricane is warm water.

During the warmer months of hurricane season, the waters in the Atlantic and Gulf of Mexico are the perfect temperature to create hurricanes. As warm, moist air rises from the water into the atmosphere, it creates an area of low pressure underneath.

This causes air from the surrounding areas to flow into the low pressure area. Eventually this air becomes heated and rises into the atmosphere, and the repeats itself.

In this way, hurricanes are kind of like a big engine with a constant supply of and . The "" is the cooler air that keeps the going. The "" is the warm air rising into the atmosphere.

As this continues, clouds and storms form, creating a giant, spinning .

When you look at satellite images of a hurricane, you may notice a hole at the center of the . This hole is called the " eye" of the hurricane.

As the eye passes over land, the weather becomes very calm. Once the eye passes, though, the winds begin again as the second part of the passes over.

Unfortunately, there is no way to stop a hurricane. They do tend to lose strength once they move over land.

Without warm water to continue fueling them, hurricanes will eventually diminish in size and speed until they disappear.

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There's a storm a-comin' today in Wonderopolis. Hang onto your hat!

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What do you get when you mix in the with thunderclouds and strong winds? Many times the answer is .

Have you ever seen hailstones - sometimes tiny, sometimes large pellets of - fall from the ? If you have, you know it can be quite a sight... and sometimes dangerous.

Hailstorms are most common in the warm spring and summer months. When thunderstorms and tornadoes increase, hailstorms usually follow close behind.

Cumulonimbus clouds - those tall, threatening clouds often called "thunderclouds" - are where hailstones begin to form. The temperatures high up in these clouds can be quite cold, causing in the to change into crystals. These crystals - sometimes called "soft " or " pellets" - are called "" by meteorologists.

As forms, the crystals become heavier and begin to fall downward. When weather conditions are right for , very strong winds - called "updrafts" - will push the back up into the upper parts of the thunderclouds.

As the ascends back into the upper parts of the thunderclouds, it accumulates more and gets bigger. This process is called "." As layers of are added, the turns into hailstones that get bigger and again begin to fall toward the Earth.

When the hailstones grow big enough to overcome the power of the updrafts, they will fall to Earth as . How big hailstones get depends largely on how strong the winds are.

Updrafts of 20 miles per hour usually result in -sized (up to 0.5 inches in ), while updrafts of 40 miles per hour can make hailstones the size of quarters (up to 0.75 inches in ).

Very large hailstones require incredibly strong updrafts. the size of a golf ball (up to 1.75 inches in ) needs updrafts of about 55 miles per hour. Softball-sized (4 or more inches in ) only forms when updrafts exceed 100 miles per hour.

The largest hailstone ever recorded in the United States fell in South Dakota on July 23, 2010. It weighed 1.93 pounds and measured 8 inches in and 18.62 inches in circumference ! Can you imagine the damage that hailstone could have caused?

Hailstorms usually don't last long - only about 5 to 10 minutes - but they can cause a lot of damage in that time. In addition to damage caused to automobiles, airplanes, skylights, and roofs, also regularly destroys farmers' crops.

Far less common - but still possible - are serious injuries. can cause concussions or fatal head to people and animals if the hailstones are large enough.

Hailstorms are most common in the Great Plains states, especially northern Colorado and southern Wyoming. If a hailstorm breaks out where you live, get inside as quickly as possible and stay away from windows.

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What do you get when you mix in the with thunderclouds and strong winds? Many times the answer is . Have you ever seen hailstones - sometimes tiny, sometimes large pellets of - fall from the ? If you have, you know it can be quite a sight... and sometimes dangerous.

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Today's Wonder of the Day was inspired by nick from AL. nick Wonders, " why do storms happen " Thanks for WONDERing with us, nick!

Have you ever heard someone talk about "the the "? If you've seen storms up close, you know there's usually nothing about them! So what are people talking about?

The calm - sometimes called a - the is a often used to refer to a period of or that comes right a time that is very busy or . When you think about it, it just makes sense.

If you're suddenly very busy with activities or lots of excitement, the period of time that started would naturally be by comparison . There's actually a little more to it than that, though.

The the got started as a sailors used to refer to an actual phenomenon they observed often at sea. You may have noticed this phenomenon from time to time, too.

For example, have you ever been playing in your backyard on a warm summer day? As you're having fun, you suddenly notice that the world around you seems quieter. The air around you is still and even the birds and other animals seem to have disappeared.

long, you start noticing changes. Clouds appear. Winds increase. You head for the house just as raindrops begin to fall from the sky. As you look out the window at the rain falling, you might wonder, "Why did it get so right the ?"

That's the same question that sailors and other people have asked for thousands of years. Fortunately, the science behind storms can help us understand the that sometimes comes them.

The fuel that storms run on is warm, air. As a approaches, it pulls warm, air from the atmosphere all around it. It can even pull air from the direction in which it's traveling.

As air is drawn into a , it leaves a low-pressure in the area it came from. The warm, air travels up through clouds, cooling and condensing as it feeds the clouds.

However, updrafts quickly push the air out of the tops of the clouds. Once it gets pushed out, it descends back down toward Earth, drawn by areas with low-pressure vacuums (or, in other words, right back where it came from!).

As the air descends, it gets warmer and drier. This warm, dry air that settles back down to Earth is stable. As it covers an area, things tend to get quiet and calm. This is the the !

Of course, things don't always happen this way. There are many different types of storms that can behave in many different ways. Sometimes storms aren't by calm. Instead, they announce their arrival with wild winds and cracks of thunder.

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Today's Wonder of the Day was inspired by nick from AL. nick Wonders, " why do storms happen " Thanks for WONDERing with us, nick! Have you ever heard someone talk about "the the "? If you've seen storms up close, you know there's usually nothing about them!

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Today's Wonder of the Day was inspired by Olivia. Olivia Wonders, " How are icicles formed " Thanks for WONDERing with us, Olivia!

Do you like to your house for the winter holidays? As winter break approaches and the weather turns cooler, many people look forward to dressing up their house with boughs of and thousands of twinkling lights.

Some of the most winter decorations are provided by Mother Nature. When temperatures drop below freezing and precipitation falls, the of your house can become suddenly with shimmering spikes of frozen water. What are we talking about? Icicles, of course!

If you've ever seen icicles up close, it's clear what they're made of: ice! Their name even gives away their composition . But how do icicles come to be? It's not like spikes of ice fall from the sky and attach themselves to the of your house.

Instead, icicles form through a natural scientific process that requires certain weather conditions. First, you need a source of frozen precipitation , such as snow or ice. If you get a of snow or ice on your , there's a decent chance you could see icicles form soon.

Next, you need a combination of below-freezing temperatures and some . The is necessary to melt some of the snow or ice to form small water drips. As the water begins to drip off the edge of a surface, such as a , the below-freezing air temperature will cause the drops to freeze again, creating the of a new icicle.

If the process ended there, icicles might look like small, icy warts along your roofline. As you already know, though, icicles eventually take on a long, thin, cone-like shape. Why does that happen?

As the Sun continues to melt snow or ice on the , water continues to drip down the slowly-growing icicle. The thin sheet of water slides down the outside of the icicle and gets colder as it reaches the bottom. At the bottom of the icicle, it refreezes and adds to the length of the icicle.

This occurs because the below-freezing air that surrounds the icicle acts like an insulating . Because heat energy rises, this insulating layer of air is thicker at the top, so the top of the icicle stays warmer. Dripping water thus continues to flow toward the bottom of the icicle, where the insulating layer is thinner and allows the drops of water to freeze again.

This thawing and refreezing cycle repeats as long as weather conditions allow, leading to the familiar icicle shape that features a wider with a long cone that becomes progressively thinner at the bottom. When the water flow that created the icicle stops, the icicle can still change shape. When temperatures are below freezing, some ice can change directly into water vapor, creating a smoother surface along the outside of the icicle.

Recently, some scientists have theorized that an icicle's shape can be described by the same mathematical that applies to a similarly-shaped natural feature of many caves: the stalactite . This idea has puzzled many scientists, since the of icicle formation is completely different than that of stalactites.

Other scientists believe that icicle formation may be much more complicated than a simple mathematical can describe. They believe many other factors, including wind, water impurities, etc., may affect icicle shape. Why bother studying this at all? Some scientists hope to understand icicle formation better, so that improvements can be made to the design of things such as airplane wings and power lines that can be negatively affected by icicles.

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Today's Wonder of the Day was inspired by Olivia. Olivia Wonders, " How are icicles formed " Thanks for WONDERing with us, Olivia! Do you like to your house for the winter holidays? As winter break approaches and the weather turns cooler, many people look forward to dressing up their house with boughs of and thousands of twinkling lights.

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Today's Wonder of the Day was inspired by Grace. Grace Wonders, " How does black ice form? " Thanks for WONDERing with us, Grace!

What are some of your favorite things to do in winter? When the weather turns cold and snow begins to fall, you probably look forward to a snow day off from school and some sledding on your favorite hill.

If you're an adult, though, that weather brings with it a special that most people would rather : driving in snow and ice. The things you take for granted under conditions , like your car exactly where you want and stopping quickly, can be and during the winter.

Even when there's no snow on the ground, driving can still be if a special type of driving hazard presents itself. You can be driving along and see something on the road ahead that looks like wet . When your car hits it, though, you can be spinning out of before you know it.

What did you run into? Weather experts call it black ice. The name is a bit . Black ice isn't actually black in color. It's also not milky white like ice. Instead, it's almost completely . Since you see right through it to the below, it often seems to be black, thus the name "black ice."

Black ice needs the right conditions to form. First, water must on the road in a very thin without splashing or wind. rainfall on a day might freeze, but it would contain air bubbles and swirls that give ice its white color.

Black ice is almost perfectly , so the source of water usually comes from fog, condensation from vehicle tailpipes, gentle, rain, or melted snow and slush. It is so thin that it can form when the surface temperature of the road is freezing even if the air temperature is above freezing.

Cold, sunless early winter mornings are a prime time to find black ice on the roads. Black ice often forms overnight when temperatures drop.

It also tends to form on bridges and overpasses, since those structures freeze before roadways. Drivers should also watch out for spots on the road that are shaded by trees or other objects, since shady areas are perfect spots for black ice to form.

What should you do if you're driving and you hit a patch of black ice? The immediate temptation is to hit the brake pedal, since you want the car to stop if you feel it sliding out of .

However, experts recommend removing your foot from the gas, keeping your wheel straight, and waiting just a couple of seconds until your tires regain some traction before trying to apply the brakes to stop. This sounds easy, but it can be difficult to remember when you hit a patch of black ice.

Experts also suggest that drivers not use cruise if black ice is possible. Turning off cruise gives the driver more over acceleration and braking in case black ice is encountered.

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Today's Wonder of the Day was inspired by Grace. Grace Wonders, " How does black ice form? " Thanks for WONDERing with us, Grace! What are some of your favorite things to do in winter? When the weather turns cold and snow begins to fall, you probably look forward to a snow day off from school and some sledding on your favorite hill.

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Today's Wonder of the Day is about a phenomenon that we've all experienced from time to time. Remember the last time you went sledding?

It was probably pretty cold outside, wasn't it? But when the wind would start to blow, it would suddenly feel much colder.

Why is that? Is it ? Nope! It's just science. Meteorologists call this phenomenon the wind chill factor.

Wind chill is what the air temperature feels like on our skin due to wind. It's always lower than the air temperature.

For example, even though the thermometer may indicate it's 35° F (1.6° C) outside, a 25-mile-per-hour wind will make it feel like it's only 8° F (-13.3° C)!

The opposite can at temperatures above 50° F (10° C). At higher temperatures, on the skin can make the air temperature feel hotter than the temperature. Meteorologists call this the heat .

It's important to note that wind chill is a prediction of what experts believe humans will the temperature to be because of the wind. No matter how fast the wind blows, the air temperature is what it is and can be measured by a thermometer .

The wind chill factor, on the other hand, is calculated using various formulas. There is no one that all scientists agree on. Most meteorologists in the United States use a accepted by the National Weather Service.

What causes the wind chill ? It's a result of the fact that the human body loses heat through a scientific process called convection .

During convection , heated air molecules rise into the air and are replaced by cooler air molecules. How quickly your body loses heat by convection depends on air flow around your body.

Your warm body usually loses heat slowly. When it's windy, though, the wind carries the warm air molecules away from your body more quickly, making you feel colder than the air temperature around you.

The faster the wind blows, the faster your body loses heat by convection . As the air temperature around you falls, the of wind is , making the wind chill greater the colder it gets.

If you've ever blown on a hot bowl of soup to cool it down before eating, you've created your own wind chill on your soup!

Even though the air temperature stays the same, the presence of wind makes us feel like it's colder outside than it actually is. The wind chill isn't all mental, though.

Since wind chill speeds up heat loss by convection , our bodies experience heat loss and react as if the temperature were as low as it feels...even if the air temperature is much higher than the wind chill factor.

Wind chill factors are calculated under the assumption that a person is properly dressed and dry. If you're not wearing suitable outdoor clothing, if your clothes are wet, or if you've been outside for an extended period of time, the wind chill factor will be even further.

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Today's Wonder of the Day is about a phenomenon that we've all experienced from time to time. Remember the last time you went sledding? It was probably pretty cold outside, wasn't it? But when the wind would start to blow, it would suddenly feel much colder. Why is that?

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"It's not the heat, it's the humidity!" Have you ever heard someone say that on a warm, day? As you'll see soon, there's a lot of truth in that statement.

To understand humidity, you first have to realize that there's in the air all around you. "But I'm not wet!" you might say. That's true. Most of the air around you has in the form of a called vapor.

is the amount of in the air. Too much or too little can be dangerous. For example, high combined with hot temperatures is a combination that can be a health risk, especially for the very young and the very old.

plays an important role in our daily . Without in the air, our might be like the on Mars. Could you imagine life without clouds, rain, snow, thunder, or lightning?

When you hear forecasters talk about humidity, you may hear them talk about two different terms: and humidity. is the amount of divided by the amount of dry air in a certain of air at a particular temperature. The hotter the air is, the more it can hold.

is the of the current to the highest possible humidity, which will depend upon the current air temperature. is the term forecasters use most often.

A of 100% means that the air can't hold any more vapor. It's totally saturated. When this occurs, it can rain. In fact, the must be 100% where clouds are forming for it to rain. However, at ground level where the rain lands, the can be less than 100%.

So how does affect us on a hot day? Humans are sensitive to changes in humidity, because our skin uses the air around us to get rid of in the form of sweat. If the is very high, the air is already with and our sweat won't evaporate. When this happens, we feel hotter than the actual temperature.

Likewise, very low can make us feel cooler than the actual temperature. This happens because the dry air helps sweat evaporate more quickly than usual.

If the temperature outside is 75° F (23.8° C), can make it feel warmer or cooler. A of 0% would make it feel like it's only 69° F (20.5° C). On the other hand, a of 100% would make it feel like it's 80° F (26.6° C).

So what's a comfortable level? Studies have shown that we tend to feel most comfortable at a of around 45%. Some people use special machines called humidifiers (add humidity) or dehumidifiers (remove humidity) to keep indoor at a comfortable level.

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"It's not the heat, it's the humidity!" Have you ever heard someone say that on a warm, day? As you'll see soon, there's a lot of truth in that statement. To understand humidity, you first have to realize that there's in the air all around you. "But I'm not wet!"

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Can you feel the ? It's around you...all the time...everywhere you go. What is it? Atmospheric - often referred to simply as air - is the exerted on you by the weight of little particles of air.

These tiny air particles, called air molecules, can't be seen, but they are all around you. They have weight, which means they constantly "push" down on you. If you look straight up in the air, you can imagine a tall of air above your head reaching all the way to the edge of the Earth's atmosphere .

The weight of that of air is the amount of air exerted on you. If you move to a higher (climb a mountain, for example), the air will be lower. Why? The length of that of air above you has decreased by the amount of your increase in .

As you move to a higher , you may notice that your ears have to "pop." This balances the between the inside and outside of your ear. Since there are fewer air molecules the higher you go, you will also probably need to faster to in more molecules to make up for the .

Air molecules also take up space. Because there tends to be a lot of empty space between air molecules, air can either fill a big area or it can be compressed to fit into a smaller area. When it's compressed, air is said to be under high .

Earth's atmosphere presses down on you with a of almost 15 pounds per square inch. You may be wondering why it doesn't feel that heavy or why you're not crushed under the weight. Remember that thing you do called breathing?

The air inside your body balances out the from air in the atmosphere , which prevents you from being squished by the of the atmosphere . You don't sense air as a , because the air inside you balances outside and you're used to that feeling.

If you watch the report frequently, you're sure to hear the weatherman talk about barometric . forecasters use a special tool called a to air .

Barometers atmospheric using , water or air. You'll usually hear forecasters give measurements in either inches of or in millibars (mb). Forecasters use changes in air measured with barometers to short-term changes in the .

Changes in air signal the movement of high- or low- areas of air, called fronts. Air molecules in high areas tend to flow toward low areas. We call this flow of air molecules wind. The larger the difference in between areas, the stronger the winds will be.

As forecasters monitor air , falling measurements can signal that bad is on the way. In general, if a low system is on its way, be prepared for warmer with storms and rain. If a high system is coming, you can expect clear skies and cooler temperatures.

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Can you feel the ? It's around you...all the time...everywhere you go. What is it? Atmospheric - often referred to simply as air - is the exerted on you by the weight of little particles of air. These tiny air particles, called air molecules, can't be seen, but they are all around you.

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What's the Difference Between Snow, Sleet and Freezing Rain?

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What's the Difference Between Snow, Sleet and Freezing Rain?

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All precipitation falls through the atmosphere on its way to the Earth's . Imagine a drop or flake falling through a long tube that contains the air between the clouds and the Earth.

The air inside the imaginary tube is the atmosphere . Differences in temperatures in different parts of the atmosphere account for the differences we see between , , and .

The liquid precipitation that falls to Earth's is . can begin as , but by the time it reaches the Earth's , it has melted because the temperature closer to Earth is warmer.

If you've ever thought it strange that it's raining when the temperature outside is below , it's probably because the temperature higher up in the atmosphere is still above .

forms in clouds at temperatures below . As falls through the atmosphere , the air remains at least 32° F or colder. In order for a to reach Earth, it must remain frozen from to .

But can it be too to ? Sometimes! The colder it gets, the less water there will be in the air...and less water in the air means less chance of .

occurs when a falls through the atmosphere and warms up a bit before refreezing. The begins its journey frozen. As it passes through a thin layer of warm air in the atmosphere , it melts a bit.

It then re-enters another pocket of air before reaching the . The refreezes and becomes an pellet we call . typically bounces when it hits the ground.

follows a similar journey as , but instead of a thin pocket of warm air, falls through a larger pocket of warm air in the middle of its journey. begins as , but when it reaches the warm pocket, it melts and becomes .

Before hitting the ground, it passes through a very pocket of air, which cools it some but not enough to turn it into . Instead, when the water droplet reaches the of the Earth and comes in contact with objects (such as cars, streets, or trees), it freezes immediately and turns into .

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What's the Difference Between Snow, Sleet, and Freezing Rain?

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All precipitation falls through the atmosphere on its way to the Earth's . Imagine a drop or flake falling through a long tube that contains the air between the clouds and the Earth. The air inside the imaginary tube is the atmosphere .

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Do you get excited when the weatherman calls for snow? If you're like many kids, you might wish for several inches of snow to fall in order to earn a snow day. When you wake to see the in a thick blanket of snow, you know it's going to be a good day filled with sledding and making snowmen!

As you watch the skies outside, waiting for the first snowflakes to from the clouds, you close your eyes to enjoy the sense of and that usually precedes the snow. Suddenly, however, you sense a bright followed by a loud ! What's going on here? It's thundersnow!

Most of the time, lightning and thunder are accompanied by rain. When we see the lightning, hear the thunder, and feel the rain, we know we're in the middle of a thunderstorm. However, in certain unique conditions, lightning and thunder can form in a storm that drops snow and hail, yielding a phenomenon meteorologists call thundersnow.

In normal thunderstorms, warm, air rises from Earth's surface to create tall, narrow updrafts that can approach 40,000 feet or more. These storms that drop rain usually occur when surface temperatures are above freezing.

Storms that produce snow are quite different from thunderstorms. Instead of tall, narrow updrafts, snowstorms usually form from broad layers of flat, shallow clouds that don't usually exceed 20,000 feet. Updrafts, if they exist, are usually rather mild.

Thundersnow occurs when normal snowstorm clouds begin to develop upward bumps, known as turrets. These turrets are caused by instability within the storm system, combined with a strong lifting mechanism. For example, a strong upper-level wind can bring in cold air, pushing pockets of colder air 5,000 or more feet above the rest of the flat clouds.

Turrets formed by the lifting action of cold air currents tend to be , leading to the presence of both updrafts and downdrafts. These cold, winds create favorable conditions for precipitation to form, including snowflakes and small hailstones known as graupel.

As precipitation particles bounce into each other, they can begin to create electrical charges. When sufficient electrical charges build up, they can be discharged in the form of -to-ground or -to- lightning, which is subsequently followed by the rumble of thunder.

Thundersnow events can often be accompanied by significant snowfall, since the conditions that lead to thundersnow also tend to large amounts of snowflakes in the flat, shallow layer below the turrets. Since thundersnow develops when air near the ground is below freezing, significant accumulation is possible from thundersnow.

If you've never experienced thundersnow, it's probably because the unique conditions for it to occur don't happen everywhere or very often. The instability and lifting necessary to create thundersnow has to occur in a very narrow, shallow layer between 20,000-25,000 feet up.

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Today's Wonder of the Day features some weird and wacky weather!

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Are you ready to take flight? Today in Wonderopolis, we're headed up, up, and way high in the sky. How high? We're traveling several miles up into the atmosphere to go sailing on a river of wind. What are we talking about? The jet stream, of course!

A jet stream is a thin of air that's several thousand miles wide and several thousand miles long. They're found almost seven miles up in the atmosphere where the troposphere meets the stratosphere at a point called the tropopause . Let us explain.

The winds in a jet stream are caused by differences in temperature between two large air masses that border the tropopause . These temperature differences create differences in air pressure between the air masses.

As colder air tries to move toward the warmer air, winds form. Because of the of Earth, these winds begin to move from west to east, creating a jet stream. The greater the difference in temperature, the faster the winds in a jet stream will move.

How fast do the winds in a jet stream usually move? Very fast! Most of the time, a jet stream moves along at over 100 miles per hour. At times, they reach speeds of over 200 miles per hour!

Jet streams were first discovered in the 1920s by a Japanese meteorologist named Wasaburo Ooishi. He used weather balloons to track upper level winds high above Mount Fuji. The term "jet stream" wasn't used until 1939, though, when a German meteorologist first used the term in a research paper.

Research and knowledge about jet streams increased during World War II, as pilots noticed variations in winds as they flew between North America and Europe. It didn't take pilots long to figure out that flying with the jet stream could decrease their travel time, while flying against the jet stream could be very difficult - if not impossible - to do.

Although there are jet streams in the Southern Hemisphere , the two strongest jet streams are both in the Northern Hemisphere . Jet streams affect worldwide weather patterns, because the strong winds can rapidly push weather systems from one area to another. Meteorologists track the position of jet streams to help predict the weather.

Jet streams shift throughout the year. In warmer weather, they move north. In colder weather, they move south. They tend to be strongest in winter, because the temperature difference between and tropical air masses is greatest at that time.

In addition to meteorologists, pilots and airline officials also pay close attention to jet streams. Flying with the jet stream can greatly reduce flight times, as well as fuel consumption . For planes traveling east to west, it's also important to keep an eye on jet streams. Pilots will fly above or below a jet stream to save time and fuel.

Would you believe that there are a few people who have walked in a jet stream? It's true! Mt. Everest is so high that its sits in a jet stream. Winds at the top of Mt. Everest routinely blow at over 118 miles per hour. This can make it very dangerous for those who climb all the way to the highest point on Earth!

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Are you ready to take flight? Today in Wonderopolis, we're headed up, up, and way high in the sky. How high? We're traveling several miles up into the atmosphere to go sailing on a river of wind. What are we talking about? The jet stream, of course!

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Today's Wonder of the Day was inspired by Maryann from AL. Maryann Wonders, " How does el nino affect the weather in the North Eastern part of the US? " Thanks for WONDERing with us, Maryann!

Do you like to keep an eye on the weather? Or do you rely on friends and family members to tell you when to pack a jacket or a raincoat? For those involved in a lot of outdoor activities, keeping an eye on the weather forecast is an important part of planning. After all, you don't want to be stuck outside without the proper clothing and gear.

Often we don't give the weather much thought unless it's making news. If you're in the middle of a long or if storms are in your area, the weather may dominate the headlines. People want to know why certain weather events occur. Did you realize that your local weather might be impacted by events thousands of miles away?

In the midst of in certain years, there's one weather phenomenon that you might hear about frequently: El Niño. But what exactly is El Niño? And how does it affect weather around the world?

El Niño is a Pacific that's one of the phases of what's known as the El Niño-Southern Oscillation (ENSO) . The ENSO involves temperature fluctuations between the and the atmosphere in the eastern Pacific near the .

During an El Niño episode, warm waters in the western Pacific shift to the east along the toward the South American coast. Instead of the warmest waters staying near Indonesia and the Philippines, these waters sit off the shore of northwestern South America during an El Niño . This is why El Niño is often known as the warm of ENSO.

If you know Spanish, you've probably already figured out that El Niño means "the little boy." It's also often interpreted as "Christ child," because Peruvian fishermen who first noticed this weather phenomenon way back in the 1600s called it El Niño de Navidad. Since El Niño tends to be strongest during December and January, the fishermen gave it a name related to the Christmas season.

Occasionally, the opposite phenomenon occurs. When trade winds blow warm water even farther west than normal, this "cold " of ENSO is called La Niña or "the little girl" to indicate it has the opposite effect of El Niño.

El Niño and La Niña cycles usually last 9-12 months. They're difficult to predict, because scientists don't fully understand what causes them to occur. El Niño cycles occur more often than La Niña cycles. Scientists estimate that El Niño cycles happen, on average, every 3-5 years, although they can happen as frequently as every two years or as rarely as every seven years.

So why does El Niño make big news when it occurs? Not only does El Niño affect Pacific processes, but it also has a major impact on global weather and . storms shift eastward, impacting both North and South America.

Strong El Niño cycles usually lead to above-average precipitation and below-average temperatures during the in the southern half of North America, while the northern half of the continent experiences below-average precipitation and above-average temperatures. Northwestern South America often sees record rainfalls during El Niño cycles. Fishing in these areas is impacted, too, as fish move north and south to seek colder waters.

The effects of El Niño aren't just limited to North and South America, though. Australia and Southeast Asia see hotter than normal temperatures, and it's not uncommon for these areas to suffer droughts. El Niño-induced droughts can also stretch as far as southern Africa and India.

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Today's Wonder of the Day was inspired by Maryann from AL. Maryann Wonders, " How does el nino affect the weather in the North Eastern part of the US? " Thanks for WONDERing with us, Maryann! Do you like to keep an eye on the weather?

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Today's Wonder of the Day was inspired by Brajone. Brajone Wonders, " What is a cold front? " Thanks for WONDERing with us, Brajone!

Is it where you live? When it starts to get colder outside, you may hear weather forecasters talk about a cold moving into your area. Have you ever WONDERed what they're talking about?

In weather terms, a is the between air masses of different temperatures. A cold is the leading edge of a mass of cooler air that is pushing warmer air ahead of it out of the way.

As a cold moves into an area, it displaces warmer air at level. Colder air is than warm air, so it pushes the warm air higher into the atmosphere . Temperature changes along the of the cold/warm air can be in excess of 50° F (10° C).

As the warm air rises, it causes an area of low pressure along the cold . The warm air cools as it rises and begins to condense.

If enough is present, a line of thunderstorms and rain can form along the edge of the cold . If the cold is , thunderstorms are more likely. Stable systems often just bring steady rains. Very cold fronts can hail storms and even tornadoes.

Cold fronts usually move from northwest to southeast. They tend to be strongest in the spring and the fall and weakest in the summer. In addition to rain and thunderstorms, they also bring , shifting winds.

Winter cold fronts might not any precipitation at all if there's insufficient in the air. If there's in the air, though, a cold can bring significant snowfall.

Cold fronts move much faster than warm fronts and can cause sharper changes in the weather. As a cold is passing through, you will notice temperatures drop quickly and then as it passes.

If you're watching the weather forecast on your local news, a cold will be marked by a solid blue line. The blue line marking the cold might also include triangles pointing in the direction the cold is moving.

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Grab a coat! Colder weather is moving into Wonderopolis today!