An air mass is a large (usually thousands of miles across) volume of air that has the same temperature and humidity. Air masses get their properties from spending days to weeks over the same part of the Earth: Examples: over central Canada, the North Pole, the tropical Pacific Ocean. Describe what the air would be like in each of these places. Warm? Cold? Wet? Dry?

If the air mass sits over the ocean for a while, it becomes humid (wet) and is called maritime. The air will have high humidity.

If the air mass sits over land for a while, it becomes dry and is called continental. The air will have low humidity.

If the air mass sits near the equator for a while, it becomes warm and is called tropical.

If the air mass sits near the poles for a while, it becomes cold and is called polar.

This means there are 4 combinations:

What do you think they will be?

Maritime tropical = wet & warm Continental tropical = dry & warmMaritime polar = wet & coldContinental polar = dry & cold

Our weather constantly changes because different kinds of air masses are being pushed around the Earth.

A weather front is a “battle” between two different air masses that are touching.

Imagine two water balloons that are filled Imagine two water balloons that are filled with water of different temperatures. If you with water of different temperatures. If you hold one in each hand and push them hold one in each hand and push them together, the places the balloons touch is together, the places the balloons touch is thethe boundary between the two balloons. boundary between the two balloons. This would be the balloon “front.”This would be the balloon “front.”

Kinds of Fronts

• Cold Fronts

• Warm Fronts

• Stationary Fronts

• Occluded Fronts

Cold Front

• A cold front occurs when a more dense air mass pushes under a less dense air mass.

                                                                               

                                                         

                

                  

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      Notice that the colder (blue) air is pushing the other air out of the way. It is “winning the pushing battle.”

Notice the symbol for a cold front!

Notice the kinds of clouds at a cold front.

Cold front facts to know:

1. Moves quickly

3. Produces cumulus first.

2. Rapid “uplift” of air occurs due to the cold air lifting the warm air.

4. Often produces severe weather (tornadoes, hail, lightning).

5. Cooler, drier air follows.

Cold front

Drier, cooler air mass

Warm Front• A warm front occurs when a less dense air mass

rides up over a more dense air mass.

Notice the symbol for a warm front!

A warmer air mass is pushing into a cooler air mass. Because warm air is less dense, it gets pushed over the cooler air mass.

Notice the kinds of clouds at a warm front.

Facts to know about warm fronts!

1. Warm air moves over cold

2. Often begins with cirrus clouds followed by stratus.

3. Produces light to moderate rain.

4. After it passes, warmer weather.

Stationary Front• A stationary front occurs when the air masses on

either side of the front are not moving toward each other. On surface maps, a stationary front is indicated by alternating the cold/warm symbols as shown.

Sometimes is you are observant, you can see the front!

Video air masses and fronts How weather systems move video

                                                                                                                                                           

                 

H stands for a high pressure air mass and L means low pressure.

Isotherm map – these lines are isothermsIso = equal therm = temperature

Wind map – these lines are isobarsIso = equal bar = barometric pressure

Doppler radar map of a hurricane crossing Florida.

Doppler radar sends out microwaves that bounce back to a receiver according to how much precipitation gets in the way.

Combination map used for TV and internet

Another combination map – Can you read it?