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Wonder of the Day #97: What's the Difference Between Snow, Sleet, and Freezing Rain?

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Wonder of the Day #97: 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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Wonder of the Day #1141: Where Does Snow Go When It Melts?

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Wonder of the Day #1141: Where Does Snow Go When It Melts?

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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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Wonder of the Day #814: Can It Snow When It’s Not Cold?

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Wonder of the Day #814: Can It Snow When It’s Not Cold?

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We hope you don’t think today’s Wonder of the Day is too flaky!

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Wonder of the Day #79: Why Are All Snowflakes Different?

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Wonder of the Day #79: Why Are All Snowflakes Different?

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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!

NGSS.PS1.A, CCRA.L.3, CCRA.L.6, CCRA.W.3, CCRA.L.1, CCRA.L.2, CCRA.R.1, CCRA.R.2,

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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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Wonder of the Day #534: Do All Mountains Wear Snowcaps?

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Wonder of the Day #534: Do All Mountains Wear Snowcaps?

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Today's Wonder of the Day was inspired by Hannah from OR. Hannah Wonders, " Why is there very little air on mountain tops? " Thanks for WONDERing with us, Hannah!

If you've ever seen the Rocky Mountains, you can't help but be taken by their . When their tops are capped with snow, they make a picture that's breathtaking .

Thinking about the of the mountains got us to thinking about why some of them have snow at the top (called a snowcap) and others don't. Since the top of a mountain is closer to the Sun, shouldn't it be warmer up there? And doesn't heat rise? So why is there snow?

The top of the mountain is actually its coldest spot. As you a mountain to a higher (), the atmosphere gets and . This is because air pressure decreases with .

Even though warm air rises, as it does so the rising air expands and cools. When it expands and cools, it can't and heat the way it does at the bottom of the mountain.

Although mountaintops are closer to the Sun, they're also farther away from the heat of the Earth's core that keeps the ground warm. So the top of the mountain can be much colder than the bottom.

In fact, the bottom of a mountain can be located in a jungle while the top of the mountain has snow on it! That's why it's possible to have snow at the .

Cooler temperatures at the top of a mountain also mean that there's less evaporation taking place. This leads to greater amounts of moisture in the air. More moisture means more rain and, at the very top of a mountain, more snow.

Not all mountains have snowcaps, and not all mountains that get snow have snowcaps all year. A lot depends upon their location and how tall they are. Mountains lower in are less likely to have snowcaps or to have them all year long.

Many mountains, though, have snowcaps year-round. Above a certain point - called the snow line - it stays cold enough that the snow never melts.

The of the snow line varies around the globe. It depends upon both ( of the mountain) and (where the mountain is located). The snow line is much higher near the (about 15,000 feet), for example, than it is near the poles (sea level or 0 feet in ).

The snow line can be affected by other factors, too. For example, in the Andes Mountains of South America, it is so dry that the mountains rarely see snow, despite their and distance from the . Monte Pissis in Argentina is the tallest mountain in the world without a snowcap.

Mountains that are near coastlines may have a lower snow line than other areas with the same and . As you get closer to a , the amount of moisture in the air tends to produce more snowfall at higher altitudes.

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Today's Wonder of the Day was inspired by Hannah from OR. Hannah Wonders, " Why is there very little air on mountain tops? " Thanks for WONDERing with us, Hannah! If you've ever seen the Rocky Mountains, you can't help but be taken by their .

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Wonder of the Day #1579: What Is Thundersnow?

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Wonder of the Day #1579: What Is Thundersnow?

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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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Wonder of the Day #769: What Causes an Avalanche?

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Wonder of the Day #769: What Causes an Avalanche?

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If you're like most kids, you may love snow. Not only can it get you out of school, but it's also fun to play with. Who doesn't love to sled and build snowmen?

Snow can also be dangerous, too. You've may have heard your parents talk about how difficult it can be to drive in snow. Car accidents aren't the only dangers created by snow, though.

If you're ever skiing in the mountains, you'll want to be aware of avalanches. An is a sudden flow of snow down a , such as a mountain. The amount of snow in an will vary based on many things, but it can be such a huge amount that it can bury the bottom of a in dozens of feet of snow.

Avalanches can be caused by many things. Some of them are . For example, new snow or rain can cause built up snow to loosen and fall down the side of a mountain. Earthquakes and the movement of animals have also been known to cause avalanches.

Artificial triggers can also cause avalanches. For example, snowmobiles, skiers, gunshots, and explosives have all been known to cause avalanches.

Avalanches usually during the winter and spring, when snowfall is greatest. As they are dangerous to any living beings in their path, avalanches have forests, roads, railroads and even entire towns.

Warning signs exist that allow experts to - and often - avalanches from occurring. When over a foot of fresh snow falls, experts know to be on the lookout for avalanches. Explosives can be used in places with massive snow buildups to smaller avalanches that don't pose a danger to persons or property.

When deadly avalanches do , the moving snow can quickly reach over 80 miles per hour. Skiers caught in such avalanches can be buried under dozens of feet of snow. While it's possible to dig out of such avalanches, not all are able to escape.

If you get tossed about by an and find yourself buried under many feet of snow, you might not have a true sense of which way is up and which way is down. Some victims have tried to dig their way out, only to find that they were upside down and digging themselves farther under the snow rather than to the top!

Experts suggest that people caught in an try to "swim" to the top of the moving snow to stay close to the surface. Once the stops, do your best to dig around you to create a space for air, so you can breathe easier. Then, do your best to figure out which way is up and dig in that direction to reach the surface and signal rescuers.

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You wouldn't want to be caught underneath today's Wonder of the Day!

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Wonder of the Day #1855: What Is Lake Effect Snow?

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Wonder of the Day #1855: What Is Lake Effect Snow?

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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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Wonder of the Day #103: Why Is Sand or Salt Put On Roads When It Snows?

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Wonder of the Day #103: Why Is Sand or Salt Put On Roads When It Snows?

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If you live somewhere that gets snow and ice in the , you've likely enjoyed a " snow day" off from school when snow and ice made the roads too for driving.

As your city works to clear snow and ice from the roads, you may have noticed trucks spilling salt or sand on the road. That's no ! It's all part of the .

In warm water, molecules move quickly and freely, making liquids and able to to any shape of you them into. As water freezes, though, molecules begin to move more slowly. Eventually the molecules begin sticking together to form ice in a process we call freezing.

When you put salt on ice, liquid water molecules that have not yet frozen on the surface of the ice a bit of the salt, creating a saltwater called "." The prevents the liquid water molecules from freezing.

As more water molecules begin to speed up and break free from the ice, they turn into liquid and even more of the salt.

Why does this happen? Salt lowers the freezing point of water. Ice forms when water is cooled to 32° F (0° C). When you add salt to water, the freezing point drops.

If you add a 10-percent salt , the freezing point drops to 20° F. A 20-percent salt freezes at 2° F.

If you have ever sprinkled salt on your icy front porch steps, you already know you can watch this process in action. When you sprinkle salt on ice, you will notice that it begins to immediately around each of salt.

This melting continues to spread, until you are left with salt grains on the porch steps. With the ice gone, the salt also provides , making it safer for visitors to come to your front door.

Unfortunately, if temperatures dip below approximately 15° F, salt may not get the job done. Salt needs water to begin the melting process.

If all the water is frozen solid, it cannot get into the ice to start the melting. When this happens, workers often turn to sand instead.

Many people believe that sand and salt are used for the same purpose - to melt the ice. But they're wrong!

While workers use salt to melt ice, they rely on sand for improved . Sand crystals increase friction and help prevent vehicle tires from slipping on slick roads, making travel easier for drivers.

Sand can also help prevent new ice from forming on roads. Imagine each of sand as a tiny little ball. In each scoop of sand, there are millions of balls constantly in motion. Each time a car drives over them or the wind blows, the grains move around.

The movement of the sand grains makes it difficult for water molecules to stick together and form ice. Although sand may not entirely prevent ice from forming, its constant motion makes it difficult for ice to build up as quickly as it can on untreated roads.

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Why Is Sand or Salt Put On Roads When It Snows?

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You may want to take today's Wonder of the Day with a grain of salt. It won't break the ice, but it will melt it!

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Wonder of the Day #1801: How Are Icicles Formed?

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Wonder of the Day #1801: How Are Icicles Formed?

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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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Wonder of the Day #2034: Have You Ever Seen Black Ice?

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Wonder of the Day #2034: Have You Ever Seen Black Ice?

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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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Wonder of the Day #494: Why Is Ice Slippery?

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Wonder of the Day #494: Why Is Ice Slippery?

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When winter weather hits and and snow abound, all sorts of surfaces can get and . If you're a driver, this is not such a good thing. and snow can make driving treacherous .

Of course, if you want to go sledding, it's a great thing! When it comes to sliding down a hill on a or a , you want the snow to pack down into that's as as possible.

No one would deny that is , but have you ever thought to wonder why? After all, is a solid, right? Can you think of any other solids that are ?

Think of a player for a moment. Can you imagine trying to on a sidewalk? How about a wooden floor? These are solids, too, so why aren't they ?

After years and years of research, scientists can explain what makes ...but not exactly why. So what makes ? The answer is definitely water - the liquid form, not the solid!

Scientists have discovered that a very thin layer of liquid water exists at the edge of - even that is extremely cold. For years, scientists believed that this thin layer of liquid water was the result of being applied to .

Water has an unusual property: its solid form () is less dense than its liquid form. This is why cubes float in a glass of water. The lower of means that its melting temperature can be lowered by applying .

So, for example, when an glides over , scientists once believed that the applied by the would lower the melting point of the solid . This would cause the layer to melt. The would then slide across on a thin sheet of water that would immediately refreeze as soon as the passed.

Unfortunately, scientists later discovered that the applied by skates or people's shoes standing on was not great enough to cause these changes. So, they had to look for another explanation. In recent years, two other theories have been developed to explain the presence of the thin liquid water layer that exists on .

One of these theories is that causes the liquid layer of water to form on . is the force that generates heat whenever two objects slide against each other. If you rub your hands together, you can feel them heat up. That's at work. When a moves over the surface of , the between the and the generates heat that melts the layer of .

But is still even when you're standing still. If you stand on without moving, no exists to generate heat, yet the is still . So there must be something else going on.

The other theory is that is just , because the layer never turns to a solid. According to this theory, the water molecules at the surface of the move more, because they're at the edge and there aren't any molecules above them to help keep them in place. As a result, the layer stays in a liquid state even at temperatures way below freezing.

So far, scientists haven't been able to decide which of these two theories is correct. Without a definitive answer at this point, it's safe to say that both theories play a role in keeping .

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When winter weather hits and and snow abound, all sorts of surfaces can get and . If you're a driver, this is not such a good thing. and snow can make driving treacherous . Of course, if you want to go sledding, it's a great thing!

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Wonder of the Day #1676: How Do Forecasters Predict The Weather? 

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Wonder of the Day #1676: How Do Forecasters Predict The Weather? 

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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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Wonder of the Day #287: Why Does It Hail?

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Wonder of the Day #287: Why Does It Hail?

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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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Wonder of the Day #479: Do All Animals Leave Tracks? 

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Wonder of the Day #479: Do All Animals Leave Tracks? 

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Did you know that the world around you - whether it's your , a neighborhood park, or even your school playground - is full of animals? It's true...even if you can't always see them.

If you know what to look for, though, you just might be able to tell what animals have been hanging around and where they went. No matter how small they may be, all animals leave some evidence behind when they move through the world.

You can track animals in your or a local park. For a real , though, visit a nearby state park or forest and hit the trails. It can be a lot of fun to be an animal detective, searching for footprints, paw prints, and prints!

As you move, your feet leave footprints that show where you've been. Animals are the same way. Of course, you can't always see these tracks easily. For example, a rabbit hopping through thick grass would not be an easy task.

Sand and hard-packed dirt can make it easier to see animal tracks. However, it's much easier to track animals traveling through snow or mud. So you might want to wait until just after it rains or snows to give a try.

Animal isn't easy, but with a little forethought and some basic information , you can identify some basic animal tracks. Before you set out on your , think about the kinds of animals you know live in your area.

For example, if you know that squirrels, rabbits, and birds live in your area, it's likely that you'll find tracks from some or all of these animals. Likewise, if you can't identify a particular track, it's probably not from a hippopotamus , , or ...unless you live in Africa!

So let's say you find an animal track. How can you tell what animal made it? Here are a few clues you can use to unravel the mystery.

If the track has four toes on both the front and back feet, you're probably looking at a track from a member of the dog family (dog, , wolf, or fox) or the cat family (cat, , or bobcat). If the track has small, triangular marks in front of the toes, those are claw marks, which mean the track is probably from a dog, not a cat.

If the track has four toes on the front foot and five toes on the back foot, it's from a rodent, such as a mouse, chipmunk, , woodchuck, or . Five toes on each of the front and back feet point toward a raccoon, a bear, a beaver, an , or a member of the weasel family, such as a weasel, badger, skunk, or otter. Two-toed tracks are usually left by deer.

Animals that hop, such as squirrels and rabbits, often leave interesting tracks. As they hop along, their bigger back feet land ahead of their smaller front feet.

When you find tracks, try to follow them as far as you can. In which direction was the animal moving? Where do you think it was going? If you're having trouble following the tracks, one trick you can use is to keep the print between you and the Sun. Doing so allows the light to cast shadows in the print to make it stand out more from its surroundings.

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Did you know that the world around you - whether it's your , a neighborhood park, or even your school playground - is full of animals? It's true...even if you can't always see them. If you know what to look for, though, you just might be able to tell what animals have been hanging around and where they went.

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Wonder of the Day #433: How Do You Sculpt Ice?

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Wonder of the Day #433: How Do You Sculpt Ice?

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Do you like art? Many children feel the to create their own masterpieces from time to time.

When you feel creative, what do you reach for? Crayons? A paint brush? A ball of clay?

You probably don't reach for a and a huge block of ice. But believe it or not, that's exactly what some artists do!

Ice sculptors use chainsaws and special chisels to works of art made out of large blocks of ice. Unfortunately, unless they're refrigerated, ice sculptures have a limited lifespan.

For this reason, they're usually created for special events, including weddings and fancy parties. Large restaurants and cruise ships also often feature ice sculptures on tables or as part of decorative food displays.

Large blocks of crystal-clear carving ice are usually created with special machines. White ice blocks that look like snow are also used from time to time.

Artificial dyes are sometimes used to create colored ice blocks for special effects. Machine-made ice blocks aren't the only source of carving ice, though.

In very cold areas, large blocks of ice can be removed by heavy machinery from frozen rivers, lakes and ponds. Frozen bodies of water used for harvesting ice carving blocks are sometimes called " ice ."

Would you like to learn how to ice? If so, you might be surprised to learn that this particular art form is usually taught in (cooking) schools, not art schools!

Since ice sculptures are used so often in conjunction with food and celebrations, schools teach the skill. Art schools typically stick to sculpting materials that last longer, such as stone and metal.

If you're interested in sculpting in nontraditional ways, there's another form of sculpture you might want to check out: butter sculpture! Butter sculptures date back to the 7th century in Tibet.

They became popular as an art form in the late 19th century in the United States. Today, butter sculptures - especially " butter cows" - are still popular attractions at state fairs.

John K. Daniels made the first "butter cow" for the 1911 Iowa State Fair. Norma "Duffy" Lyon, also known as "The Butter Cow Lady," took butter sculpture to a new level, creating likenesses of John Wayne, Elvis Presley and The Last Supper out of nothing but butter.

A typical "butter cow" is made by layering butter on a frame built of wood or wire. Smaller amounts of butter are then used to create fine details.

An average "butter cow" requires 500 to 600 pounds of butter, which is equivalent to about 2,400 sticks or enough butter for 42,000 cookies!

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Do you like art? Many children feel the to create their own masterpieces from time to time. When you feel creative, what do you reach for? Crayons? A paint brush? A ball of clay? You probably don't reach for a and a huge block of ice.

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Where Does It Snow the Most?

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Today's Wonder of the Day was inspired by Wendy. Wendy Wonders, " Which state gets the most snow? " Thanks for WONDERing with us, Wendy!

When the weather turns cold, there's one thing that almost all children look forward to: a snow day! Sure, school is great and all, but there's just something special about waking up to a of white snow on the and knowing you get to sleep in and then play in the snow the rest of the day.

While some people would take beaches and palm trees every day of the year, there are of people who don't mind a bit of snow now and then. Those who love the Christmas season usually love snow, especially when it falls on Christmas Eve!

If you're a huge fan of snow, then you might want to moving somewhere where you're sure to get lots of it each year. But where would that be? As it turns out, there are many places around the world that get lots of snow every year.

If you want to live in the United States, you could move to Mt. Washington, New Hampshire. It holds the for the most days with measurable per year at just over 118 days! On , Mt. Washington receives more than 23 feet of snow per year.

If you to be on the other , move to Paradise...Paradise Ranger Station on Mt. Rainier in Washington, that is! This in the Pacific Northwest has been known to receive over 56 feet of snow .

If nothing but the snowiest place on Earth will satisfy you, then you need to move to Japan. Specifically, you need to move to the northern Japanese Alps of Honshu Island. Cold Siberian winds dump amounts of snow on these mountains. How much?

Some experts estimate annual in the mountains to be 1,200-1,500 inches! In 1927, the snow depth on Mt. Ibuki was measured to be over 465 inches.

The snow in these mountains has become a popular tourist attraction . A highway through the mountains is regularly cleared to keep it open all winter. It's known as the Yuki-no-Otani Snow Canyon, and people stop along the road to take pictures of their vehicles surrounded by walls of snow as tall as 60 feet!

Some people are surprised that Antarctica doesn't make the list. The reason is because the South Pole is one of the driest places on Earth. Due to the lack of moisture in the atmosphere , the South Pole only receives about two inches of snow each year!

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Today's Wonder of the Day was inspired by Wendy. Wendy Wonders, " Which state gets the most snow? " Thanks for WONDERing with us, Wendy! When the weather turns cold, there's one thing that almost all children look forward to: a snow day!