Air Fronts

Lesson Plan - Get It!

Audio:

• What is an air front, exactly?

An air front is the front of the air. Good work! Lesson over.

Actually, there's a bit more to it than that. There are "bubbles" of air, called air masses, that are constantly moving everywhere on Earth. You may currently have a cold and dry air mass (cP) over you right now, but a warm, wet air mass (mT) could move in tomorrow. If you'd like a review on air masses, check out the Elephango lesson under Additional Resources in the right-hand sidebar.

When one air mass pushes another air mass, this creates an air front. Our original definition wasn't too far off. The air front is the front of the air mass that is doing the pushing. For example, if a warm air mass pushes a cold air mass, then we would call the border between the air masses a warm front.

The front is the place where two (or more!) air masses interact. The interaction causes some things to happen.

• Where does warm air go?
• What about cool air?

If you need a reminder on heat transfer, refer to the Elephango lesson found under Additional Resources in the right-hand sidebar.

Use your colored pencils to draw a convection current on a sheet of paper. Red represents warm and blue is for cold. If you want to get fancy, you can throw in some pinks and teals, too. Use arrows to show where the air is moving.

• How does convection affect air fronts? Let's examine a warm front to find out.

When a warm front is produced by a warm air mass pushing a cooler air mass, the less-dense warm air will rise.

As the air rises, it cools, expands, condenses, and creates clouds. Generally, precipitation also occurs, assuming there is enough moisture (water vapor) in the air. As the warm front pushes the cool air out of an area, the precipitation is pushed out as well, leaving warm and generally dry conditions.

Watch Strong warm front rolling in, July 17th 2009, from jakobherning76, to see an example in Denmark:

Let's draw a profile (side-view) of a warm front. Use your red colored pencil to show warm air pushing into blue, cool air.

• Where does the air go?
• What happens next?

Show it all in your diagram!

If you're stuck making any of these diagrams, use Weather Fronts, from WeatherSTEM, to simulate all of the fronts online.

A cold front is similar in that warm and cool air are colliding, but this time, the cool air is pushing the warm.

The cool air stays low to the ground due to its higher density, creating a wedging effect. The warm air mass is being cooled all along this wedge. This change in temperature causes the warm air to quickly condense into clouds, which causes precipitation, and even severe weather, such as thunderstorms and hail. Cold fronts are notorious for causing stormy weather. You may have noticed this when a quick summer storm is followed by noticeably cooler temperatures.

Notice how quickly the clear skies turn into clouds and rain in this TimeLapse 27-07 - Cold Front Joy, from JWHv1:

Go back to your paper and create another diagram, this time showing a cold air mass pushing into a warm one. Don't forget to show the precipitation and storms!

Now you know that a warm front happens when warm air pushes cold and a cold front happens when cool air pushes warm. Easy, right? Not so fast. The other fronts aren't quite as straightforward.

One of these other air fronts is called a stationary front.

*

Not stationery; stationary! Stationary means "not moving," like a stationary bike.

A stationary front is created when a warm air mass and cool air mass are touching, but neither one is forceful enough to push the other one. Since the air masses are coming in contact with each other, the warm air mass is cooled by the cold air mass. This cooling once again causes precipitation, just as it does with cold and warm fronts. The difference is that this precipitation isn't going to leave the area anytime soon.

Use your colored pencils to draw a stationary front: one warm air mass and one cool air mass touching but not moving.

• What's happening at the boundary?

Draw it!

Stationary fronts stay in the same location for a long time — several hours, or even days. Unfortunately, this also means that the cloudy, rainy weather will stay in the same location. Until winds pick up, that is, and the front moves out of the area.

The last type of air front is called an occluded front. An occluded front is created when a fast-moving cold air mass overtakes and occludes, or forces up, a warm air mass. Picture the cold air mass and warm air mass playing tag. The cold air mass is "It," and is chasing the warm air. Eventually, the cold air catches up to the warm air; but rather than simply say "Tag, you're it," the dense cold air dives under the warm air and forces the warm air to rise upwards.

You can probably guess what happens next. Once again the warm air rises, expands, and cools, causing clouds and rain. There is a lot of interaction between the warm and cool air masses because they are literally on top of each other, so this creates a LOT of precipitation.

Add another diagram to your collection. An occluded front looks like a red balloon of air floating in a sea of blue, cool air.

Watch What are weather fronts and how do they affect our weather?, from Met Office - Learn About Weather, to help you perfect your diagrams:

Now, don't remain stationary, but move on to the Got It? section for a review.