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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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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.

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Fronts | Climate Education Modules for K-12

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Fronts | Climate Education Modules for K-12

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A surface weather map for Jan. 1, 2013, shows a cold front (blue line with triangles) over the South, a warm front (red line with half-circles) extending from South Dakota into central Canada and a trough (blue dashed line) meandering across much of the United States.

Credit: NOAA.gov.

A weather front is a term used in meteorology to describe the front end or advancing edge of an air mass that will soon replace the air mass that's over a specific region. These air masses are designated P for "polar" (cold), T for tropical (warm), M for maritime (wet) and C for continental (dry).

The NOAA Central Library U.S. Daily Weather Maps Project is an interesting and potentially valuable weather resource for researchers. The website provides access to historical daily weather maps from 1871 thru 2003. Virtually every weather government map that was published during that 132 year time span - more than 48,000 of them - are available here. If you were to check out the maps that were published prior to Aug, 1, 1941, you might notice that something was missing. There were no weather fronts plotted!

In 1919, Jacob Bjerknes, son of a noted Norwegian meteorologist, Vilhelm Bjerknes, announced his discovery of air masses and fronts. Prior to that, it was thought that if today happened to be colder, it was simply yesterday's air with some heat that was lost to space. Or if today turned out to be warmer, then it was assumed that it was yesterday's air with some heat added in. But Bjerknes realized that there were masses of colder and warmer air that swept across the globe and bumped into each other and in the process produced zones of unsettled weather near and along their respective boundaries.

More than two decades would pass before frontal lines were incorporated into the daily weather map. But exactly what are they and what type of weather might they be expected to produce?

Cold fronts are marked on weather maps with the symbol of a blue line of triangles/spikes (pips) pointing in the direction of travel, and are placed at the leading edge of the cooler air mass. That cold/dense air wedges its way under the warm air out ahead of it.

Cold fronts are very much like atmospheric plows, pushing away warm, moist air and replacing it with a cooler and drier air mass. Another good metaphor for a cold front is that it's like a hand plane. When the cutter or sharpened metal plate is pushed forward over a wood surface it slices shavings of wood that curl upward in advance of the cutter. With the cold front, warm air is rapidly forced upward (like the shavings) in advance of the actual front (the "cutter"), creating towering cumulus clouds, some hard showers and quite possibly a few gusty thunderstorms followed by a push of cooler and drier air in its wake.

In some cases, there doesn't seem to be much of a difference temperature-wise between the air ahead of a cold front and the air moving in behind it; so it's not so much the difference in temperature as is the difference in terms of a moist and humid air mass being displaced by a significantly drier and less humid air flow. Then we might speak of the frontal boundary not so much as a "cold" front as opposed to representing a "dry" front.

Cold fronts generally advance at average speeds of 20 to 25 mph. toward the east - faster in the winter than summer - and are usually oriented along a northeast to southwest line. Winds out ahead of a cold front tend to blow from the south and southwest, and then shift after the frontal passage (called a "fropa" by meteorologists) into the northwest.

But on occasion, a cool air mass might build up over eastern Canada and sink southward through northern New York and New England. The result is a cold front that advances toward the west and south. Such a scenario is called a "back door" cold front and usually occurs during the spring and summer months. In the spring, when many are yearning for milder temperatures to take hold, a back door front is looked upon as set-back, with temperatures falling from unseasonably balmy levels back to chilly or even cold levels. Conversely, in the summer, back door fronts can be a welcome change, as a sweltering heat wave can suddenly be brushed aside as front coming in from the north or northeast ushers in a cool, refreshing breeze.

Warm fronts are marked on weather maps with a red line of half circles pointing in the direction of travel and mark the edge of an advancing warm air mass; a flow of warmer air that overtakes and replaces colder air. They are usually found on the east side of low-pressure storm systems. Since the cold air is denser than the warm air, the cold air hugs the ground. The lighter warm air slides up and over the cold air (called "overrunning") and lacks any direct push on the cold air. Thus, the cold air is slow to retreat in the rapid advance of the warm air. This slowness of the cold air to retreat produces an atmospheric slope that is more gradual than the sharper slope that accompanies a cold front.

The sensible weather associated with a warm front can stretch for as much as a thousand miles out ahead of it and as much as 36 to 48 hours prior to its actual arrival. Increasing moisture ahead of the warm front first arrives in the high levels of the atmosphere in the form of thin, wispy cirrus (ice crystal) clouds. You might even catch sight of a halo around the sun or moon; sailors would interpret this as a sign that weather was likely to turn unsettled within the next 18 to 24 hours. And indeed, with the passage of time, these thin clouds gradually lower and thicken and eventually a steady light rain or drizzle will start to fall. Near the actual frontal boundary, precipitation tends to become steadier and heavier and there could also be areas of fog as well.

Warm fronts are seldom as well marked as cold fronts, and they usually move about half as fast, at about 10 to 15 mph, and sometimes even slower. This is why precipitation associated with warm fronts is, generally speaking, of a long duration.

And especially during the winter months, the cold air that a warm front is attempting to displace is often heavy and dense and is stubborn to dislodge. As a result, the shape of some warm fronts end up contorted, seemingly looping around the colder air mass.

Stationary fronts are depicted by alternating red half-circles and blue spikes (pips) pointing in opposite directions, indicating no significant movement. When neither air mass is replacing the other, the frontal boundary becomes more-or-less stationary; the opposing forces exerted by adjacent air masses of different densities are such that the frontal surface between them shows little or no movement (sometimes also referred to as a "quasi-stationary" front). In such cases, the surface winds tend to blow parallel to the frontal zone. The resultant weather is usually low cloud cover and long duration precipitation, and not much in the way of wind.

Should the front "buckle," a wave of low pressure could develop on the front and then ripple along it to the east or northeast. Sometimes more than one wave of low pressure develops along the front, while on other occasions; a singular wave of low pressure will form and then strengthen as moves off to east or northeast, taking the trailing end of the front right along with it.

Cold fronts almost always travel faster than warm fronts and eventually they catch up to it. When this happens the warm air is forced up away from the ground, and their associated low pressure system is said to be occluded. The point of occlusion is also known as the "triple point" out of which extends a cold front to the south, a warm front extending to the east and the occluded front, which extends north back to the center of low pressure.

Storm systems usually reach their greatest intensity when they first become occluded; they then begin to weaken gradually over the next few days as the air in the storm 'mixes up," the differing air masses and the temperature contrasts are destroyed. This deprives the storm of its energy source, and so it ultimately dies. Occluded frontal passages are usually marked gusty winds and bouts of heavy rain, perhaps even thunderstorms. They are marked on the weather map by a purple line with alternating half-circles and triangles pointing in their direction of travel.

Finally, a trough (pronounced "trof") is an elongated region of relatively low atmospheric pressure, often associated with fronts that can occur either at the Earth's surface or at higher altitudes. Air pressure is lower along the axes of the trough than on its two sides. Sometimes, the isobars with a trough have a pronounced V-shape. Active weather fronts always lie within troughs, but not all troughs are frontal. The passage of an upper level trough might make its presence felt by producing a build-up of clouds, followed by a quick shot of precipitation, then clearing skies.

Unlike fronts, there is no universal symbol for a trough on a weather chart. In the United States, for instance, a trough is delineated by a black dashed line. In Great Britain, it is depicted by a bold line extending from a low pressure system, while in Australia it's a dotted line.

For the Latest Information on Weather, Visit:

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A weather front is a term used in meteorology to describe the front end or advancing edge of an air mass that will soon replace the air mass that's over a specific region. These air masses are designated P for "polar" (cold), T for tropical (warm), M for maritime (wet) and C for continental (dry).

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An air mass is a large body of air that has similar moisture (density) and temperature characteristics. A front is a transition zone between two air masses.

A cold front is a warm-cold air boundary with the colder air replacing the warmer. As a cold front moves into an area, the heavier cool air pushes under the lighter warm air that it is replacing. The warm air becomes cooler as it rises. If the rising air is humid enough, the water vapor it contains will condense into clouds and precipitation may fall.

As the cold front moves, warm, moist unstable air is usually replaced by cold, dry stable air.

A warm front is the boundary between warm and cool (or cold) air when the warm air is replacing the cold air. Warm air at the surface pushes above the cool air mass, making clouds and storms. Warm fronts often bring stormy weather. Warm fronts often form on the east side of low-pressure systems where warmer air from the south is pushed north.

A warm front typically replaces cool dry air with warm moist air.

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An air mass is a large body of air that has similar moisture (density) and temperature characteristics. A front is a transition zone between two air masses. A cold front is a warm-cold air boundary with the colder air replacing the warmer.

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Weather Fronts -- TeachPower.net Lesson - YouTube

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Weather Fronts -- TeachPower.net Lesson - YouTube

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http://www.teacherspayteachers.com/Product/24-Earth-Science-PowerPoints-PART-1 Preview of one of 160+ Powerpoint presentations that I use in my middle and high school science class that you can also find on my teacher resource website link above. This presentation covers information on air masses and which ones affect each part of the continent of North America as well as how these air masses clash and create fronts where weather is created.

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Understanding Weather Fronts: Types & Their Effect on Weather - Video & Lesson Transcript | Study.com

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Understanding Weather Fronts: Types & Their Effect on Weather - Video & Lesson Transcript | Study.com

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What Are Weather Fronts?

A long time ago, armies didn't have guns, grenades or fighter jets. They fought on the ground, face to face. An army ready to fight would consist of lines of men, each line with a specific job. In general, the front line was a strong line of shielded soldiers forging ahead, protecting those behind it.

Weather fronts act just like the front line of an army. Fronts are contact zones between two different air masses, and you can think of the air masses as the advancing armies, just with different pressure, density, temperature and moisture. And just like there's conflict between the battling armies, air masses 'battle' along fronts, creating changes in weather conditions. There are four types of fronts, and the type of front we get depends on which type of air mass, or army, is advancing over the other.

A cold front is the contact boundary of an advancing cold air mass over a stationary warm air mass. Conversely, a warm front is the contact boundary of an advancing warm air mass over a stationary cold air mass. This makes sense - the front is described by the type of air mass winning the 'fight.'

On a weather map, you'll see these symbols for a cold or warm front. The color helps you identify which type of front is moving in (blue for cold, red for warm), and the arrows tell you which direction the advancing air mass is coming from.

A stationary front is just what it sounds like: When neither air mass is advancing over the other. They are both stationary, and so is the front - the armies are at a stalemate. Finally, an occluded front is when a cold front overtakes a warm front. This happens because cold fronts move faster than warm fronts, so it's like one army is sneaking up from behind and taking over in a surprise attack.

On a weather map, you will see these symbols for a stationary or occluded front. As you can see with the stationary front, neither air mass is advancing. With an occluded front, the cold air mass is advancing over the warm air mass from behind.

How Fronts Affect Weather

Just because they didn't have machine guns or grenades doesn't mean that battles weren't bloody. When two opposing armies fight, things can get very violent and dangerous because each side believes very strongly in what they're fighting for.

Weather fronts do the same thing - they advance forward, creating weather changes and sometimes even violent storms along the front. This is like the front line of battle on both sides - the initial point of battle contact.

Thunderstorms are common along cold fronts. This is because when a cold front occurs from a cold air mass moving into a warm air mass, the warm air is forced upward. When warm air rises, it cools, and since cool air can't hold as much moisture as warm air, the water in the air gets forced out, which is what creates clouds. Since the air is moving straight up, it forms a vertical cloud, which leads to thunderstorms along the front. However, behind the front, the skies are clear and the weather is calm.

Along warm fronts, storms are less intense and more drawn out. This is because the warm air moving in over the cold air rises gradually instead of quickly. Along the front, expect overcast skies and drizzle or light rain. Behind the front, the air will be warm and clouds will be pretty scattered.

Think about it like this: Thunderstorms generally develop quickly and are very dramatic storms. This comes from the quick, dramatic rise of the warm air when a cold air mass moves in. You know how it feels when you jump into a cold pool? It's a shocking feeling, and you're likely to jump right back out! When you step into a warm hot tub though, it's a little less dramatic, and your body reacts much more gradually. The same thing happens with a warm front, when the warm air slowly moves up over the cold air mass it's taking over.

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understanding weather fronts: types & their effect on weather - video & lesson transcript | study.com

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Understanding Weather Fronts: Types & Their Effect on Weather - Video & Lesson Transcript | Study.com

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A long time ago, armies didn't have guns, grenades or fighter jets. They fought on the ground, face to face. An army ready to fight would consist of lines of men, each line with a specific job. In general, the front line was a strong line of shielded soldiers forging ahead, protecting those behind it.

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Weather Wiz Kids weather information for kids

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Weather Wiz Kids weather information for kids

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Weather Forecasting

How do meteorologists forecast the weather?
Weather forecasting is a prediction of what the weather will be like in an hour, tomorrow, or next week. Weather forecasting involves a combination of computer models, observations, and a knowledge of trends and patterns. By using these methods, reasonable accurate forecasts can be made up to seven days in advance.

What are weather station symbols?
Weather symbols are used on my weather maps as shorthand for the conditions at weather observing stations.
Click Here to see a complete list of all the weather station symbols.
Click Here for an easy print out of the different weather station symbols.

What is a High Pressure System?
A high pressure system is a whirling mass of cool, dry air that generally brings fair weather and light winds. When viewed from above, winds spiral out of a high-pressure center in a clockwise rotation in the Northern Hemisphere. These bring sunny skies. A high pressure system is represented as a big, blue H.

What is a Low Pressure System?
A low pressure system is a whirling mass of warm, moist air that generally brings stormy weather with strong winds. When viewed from above, winds spiral into a low-pressure center in a counterclockwise rotation in the Northern Hemisphere. A low pressure system is represented as a big, red L.
H
What is a dew point?

What is an air mass?
An air mass is an extremely large body of air whose properties of temperature and moisture content (humidity), at any given altitude, are fairly similar in any horizontal direction. Air masses can cover large (hundreds of miles) areas. Air masses can control the weather for a relatively long time period: from a period of days, to months. Most weather occurs along the periphery of these air masses at boundaries called fronts. There are 4 general air mass classifications categorized according to the source region: polar, tropical, continental and marine.
The dew point is the temperature at which water starts to condense out of a particular air mass. The dew point temperature changes only when the moisture content of the air changes. The higher the dew point, the greater the moisture content is in the air.
What is humidity?
What type of air masses affect the United States?
Humidity is the amount of water vapor in the air.

What is relative humidity?
Relative humidity is the ratio of water vapor contained in the air compared to the maximum amount of moisture that the air can hold at that specific temperature and pressure. Humans are very sensitive to humidity, as the skin relies on the air to get rid of moisture. The process of sweating is your body's attempt to keep cool and maintain its current temperature. If the air is at 100-percent relative humidity, sweat will not evaporate into the air. As a result, we feel much hotter than the actual temperature when the relative humidity is high. If the relative humidity is low, we can feel much cooler than the actual temperature because our sweat evaporates easily, cooling us off. What is a front?
A front is a boundary between two different air masses, resulting in stormy weather. A front usually is a line of separation between warm and cold air masses.

How do you identify a front on a surface weather map or by your own weather observations?
L
What is a cold front?
A cold front is a boundary between two air masses, one cold and the other warm, moving so that the colder air replaces the warmer air. A cold front is represented as a blue line with the teeth pointing toward the direction on movement.

What is a warm front?
A warm front is a boundary between two air masses, one cool and the other warm, moving so that the warmer air replaces the cooler air. A warm front is represented as a red line with half circles pointing toward the direction on movement.

What is a occluded front? What is a trough?
An occluded front is a combination of two fronts that form when a cold front catches up and overtakes a warm front. An occluded front is represented as a purple line with teeth and half circles. What is a stationary front?
A stationary front is a boundary between two air masses that more or less doesn't move, but some stationary fronts can wobble back and forth for several hundred miles a day. A stationary front is represented as an alternating warm and cold front symbol.

1.) Polar latitudes (P) - located poleward of 60 degrees north and south

2.) Tropical latitudes (T) - located within about 25 degrees of the equator

3.) Continental (c) - located over large land masses, dry

4.) Marine (m) - located over the oceans

What is a weather satellite?
A weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be either polar orbiting, seeing the same swath of the Earth every 12 hours, or geostationary, hovering over the same spot on Earth by orbiting over the equator while moving at the speed of the Earth's rotation. These meteorological satellites see more than clouds and cloud systems. City lights, fires, effects of pollution, auroras, sand and dust storms, snow cover, ice mapping, boundaries of ocean currents, energy flows, etc., are other types of environmental information collected using weather satellites.
We can then make combinations of the above to describe various types of air masses.
What is radar?

How does Doppler Radar work?

What is NEXRAD Radar?
The National Weather Service has installed a new type of Doppler Radar called NEXRAD Radar. NEXRAD stands for Next Generation Radar. This radar produces many different views of storms and rain that allows meteorologists to determine if a storm could be severe. Can animals predict weather?
If your dog always comes inside right before it rains, you may think that animals can predict the weather. It's probably more accurate to say that animals react to certain environmental signals that accompany weather changes, not to the weather itself. A prevalent opinion is that animals can detect certain events, like earthquakes, as soon as they happen, even if the originating event is a great distance away. The majority of researchers say that animals make greater use of their existing five senses, especially when compared to humans. The most critical sense is hearing.
Doppler Radar gets its name from the Doppler Effect. Have you ever listened to a train whistle as it was coming toward you? You probably noticed that the pitch of the whistle changed as the train passed you and moved away. This change in the frequency of sound is called the Doppler Effect. Doppler Radar measures the changes in the frequency of the signal it receives to determine the wind. Weather Forecasting Activities
Lesson Plan: Here is a great lesson plan on learning how to forecast. In this activity, kids learn about different forecasting tricks. What is Doppler Radar?
Doppler Radar detects precipitation intensity, wind direction and speed, and provides estimates of hail size and rainfall amounts. Doppler Radar gives forecasters the capability of providing early detection of severe thunderstorms that may bring strong damaging winds, large hail, heavy rain, and possibly tornadoes. Combined with satellites, radar gives forecasters the ultimate tools to provide accurate forecasts and advanced severe weather warnings.Lesson Plan: Here is a great lesson plan on weather symbols for younger kids. This lesson plan requires kids to match the weather symbols to words. You will need to download this file to then be able to print off copies for your students.
Radar is an electronic instrument, which determines the direction and distance of objects that reflect radio energy back to the radar site. It stands for Radio Detection and Ranging. This is what meteorologists use to see rain or snow.
The Doppler Effect Experiment: Here is a an experiment that teaches kids what the Doppler Effect is. They can learn how the Doppler Effect works and why Doppler Radar is such an important tool in weather forecasting.

cP continental polar cold, dry, stable

cT continental tropical hot, dry, stable air aloft, unstable surface air

mP maritime polar cool, moist, and unstable

mT maritime tropical warm, moist, usually unstable

Science Fair Project Ideas: Here is a complete list of science fair project ideas. Discover the science behind the weather that impacts us every day.
There are many types of air masses that can affect the U.S., since it is such a large country. Below are a few examples:

cP - wintertime bitter cold can extent to Southern U.S. and even Florida causing crop damage. Require long, clear nights, which means strong radiational cooling of air near the surface. A stable air mass. Little moisture added so air is dry

mP - Winter cP air moves over a region such as the NE Pacific, picking up some warmth and moisture from the warmer ocean. In the case of the Pacific NW mountains force the air to rise (orographic lifting) causing rain.

mT - wintertime source for the SW U.S. is the subtropical East Pacific Ocean. mT air that influences weather east of the Rocky Mountains comes from the Gulf of Mexico, but only influences winter weather in the SE states. Occasionally, slow moving weather systems in SW flow aloft can draw up moisture at mid and low levels producing precipitation.

cT - Continental tropical air usually only influences the U.S. in summertime as warm, dry air is pumped up off of the Mexican Plateau. It is usually fairly stable and dry, and if it becomes stagnant over the Midwest, results in a drought. Deaths associated with the 1995 heat wave in the Midwest were the result of cT and mT air which stagnated over the central and eastern part of the U.S.

Look for: Sharp temperature changes over a relatively short distance, change in moisture content, rapid shifts in wind direction, pressure changes, clouds and precipitation patterns.

A trough on a weather map is an elongated area of relatively low pressure. Troughs bring cloudy and rainy weather. A trough is represented by a hash mark line.

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Weather Wiz Kids weather information for kids

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Weather Wiz Kids is a fun and safe website for kids about all the weather info they need to know. It contains tools for weather education, including weather games, activities, experiments, photos, a glossary and educational teaching materials for the classroom.