What happens when warm air collides with a cold front? choose all that apply.

Updated April 17, 2018

By Ethan Shaw

Most people understand the basics of cold and warm fronts: Passage of a cold front cools things down, and passage of a warm front warms things up. But warm fronts and cold fronts don’t simply follow one another in orderly procession. They can also merge in what’s known as an occluded front, an important stage in the development of many of the great weather-making low-pressure systems known as midlatitude cyclones.

When a cold front overtakes a warm front, it creates what's called an occluded front that forces warm air above a frontal boundary of cooler air masses.

Midlatitude (or extratropical) cyclones – which shouldn’t be confused with tropical cyclones or hurricanes – form along weather fronts, which are boundaries between air masses of different temperatures and associated conditions. A wave along the front creates a low-pressure disturbance, which draws in winds that – because of the rotation of the Earth – spiral around the low. The leading edge of the warm air mass, where it rises over denser cold air, creates a warm front; that of the cold air mass behind, which shoves under the warm sector behind the warm front, creates a cold front.

In an occluded front, the trailing cold front overtakes the preceding warm front. This is conventionally described as the cold front “catching up” to the warm front. However, while it’s true that cold fronts tend to move faster than warm fronts, recent research suggests more underlying cyclonic processes cause the frontal mashup. Regardless, an occluded front involves the warm air behind the warm front behind forced aloft, the low-pressure center of the cyclone moving away from the frontal boundary, and the cold front coming into contact with the cold air mass originally downwind (so to speak) of the warm front.

Two types of occluded front exist: the warm-type and the cold-type. They’re distinguished by the relative temperatures of the air mass ahead of the occlusion – in other words, the air mass ahead of the original warm front – and the air mass behind the cold front. If the air behind the cold front is colder than the air ahead of the occlusion, it shoves beneath that air (because it’s denser) to form a cold-type occluded front. If the air behind the cold front is warmer than the air ahead, it rides over it to form a warm-type occluded front – which appears to be the more common case. In either situation, the lighter warm air representing the air mass originally between the warm and cold fronts sits above the boundary between the two cooler air masses.

Colored weather maps represent cold fronts with blue lines studded with blue triangles pointing in the direction of the front’s movement. Warm fronts appear as red lines marked with red half-circles that also point toward the direction of frontal movement. An occluded front shows on the map as a combination of these symbols: a purple line alternating with purple triangles and half-circles.

A forward-moving front, whether warm or cold, causes one air mass to lift above another; by forcing the air mass to its condensation level, this creates clouds and often precipitation. Weather along an occluded front can take many forms, but some combination of cold-front and warm-front effects often takes place, with anything from light to heavy precipitation often diminishing to clear skies after the front’s passage.

Author: Maddie Van Beek Before we get going, think about these questions: How often do you watch the weather on TV? What kind of weather conditions have you seen reported? What kinds of weather conditions have you experienced in your lifetime? How has weather impacted your life?  Get your brain warmed up! Write about a specific weather memory.  Make a connection: Why would you need to pay attention to the weather? Can you think of a time that knowing the approaching weather would be important?  Predict: Before you read ahead, hypothesize what do you think creates or influences weather conditions. Write down any guesses you think of! 

When you were thinking of what might influence or change the weather, did you ever think of air masses? Air masses are extremely important to consider when predicting what the weather may be like! 

According to education.com, an air mass is a large body of air with consistent temperature and humidity. When air masses form, they are taking on the temperature and humidity characteristics of the region they are in. The density of an air mass depends on the temperature and humidity levels. Warm or humid air masses are less dense then cold or dry air masses. 

This is because a molecule of water has a smaller mass than a molecule of oxygen or nitrogen (a large percentage of dry air molecules are nitrogen). 

Here’s a little more information about fronts:

“Vilhelm Bjerknes (1862-1951), a Norwegian physicist and meteorologist, coined the term front to describe the boundary between warm and cold air masses. The leading edge of a warm air mass advancing into a region occupied by a cold air mass is called a warm front. A cold front occurs when a cold air mass advances into a region occupied by a warm air mass. If the boundary between the cold and warm air masses doesn't move, it is called a stationary front. The boundary where a cold air mass meets a cool air mass under a warm air mass is called an occluded front. At a front, the weather is usually unsettled and stormy, and precipitation is common." 

http://www.edinformatics.com/math_science/3_warmcoldfronts.jpg

Analyze the visual and explain what you see.

As the warm front approaches, there may be fog or increasing rainfall, and thunderstorms may form, as well. This is due to the (usually) higher humidity in the air of warm fronts compared to that of cold fronts. Because warm air is less dense than cold air, the warm air rises as it runs into the cold air, which is followed by condensation and cloud-forming. 

Similar events happen when a cold front encounters a warm front, except they happen more quickly. Because cold air is denser than warm air, cold fronts are able to force warm air out more quickly. The cold air pushes the warm air upwards, which may be followed by precipitation or storms due to moisture in the air. 

Don’t quite get it? Try out this air mass activity to help you better understand air masses before we move on! 

Check out this video to see a demonstration similar to the activity we will do next!

Here’s another similar example. Think about how this demonstration is similar to the one we already watched. What did these experiments have in common? What are they demonstrating? How are the demonstrations different? Do the differences show us different things, or are they basically two different ways to show use the same concept? Explain. 

Let’s try this on our own! 

Our task today, using food-colored cold and hot water as a visual, is to find out what happens when a warm front and a cold front collide. 

Hypothesize: What do you think will happen when you combine warm water and cold water? Will they mix immediately? If not, how long do you think it will take to mix? 

YOU WILL NEED:

• Writing utensil
• Paper
• Blue crayon or marker
• Red crayon or marker
• 10-gallon aquarium or container
• Piece of cardboard
• Scissors
• A large spoon
• Five gallons of very cold water (you may refrigerate the water in advance or put it in the freezer to chill it) 
• Blue and red food coloring
• Five gallons of very hot water (you may use the stove or microwave to heat the water, but ask an adult for help) 
• Timer 

2. Measure the tank’s width and height, and then use those measurements to cut a piece of cardboard of identical measurements. Use the ruler to draw a straight line where you will cut the cardboard in order to make sure your piece of cardboard is cut as exactly as possible. 

3. Place the piece of cardboard in the middle of the aquarium so that it fits snugly and can stand on its own. From an aerial view, you would see something like this:

4. Make sure the cardboard fits snugly, as it needs to keep water from passing through the center of the aquarium for at least one minute! 

5. Next, grab your container of cold water and your container of hot water. Color your cold water with blue food coloring and your hot water with red food coloring. Add the desired amount of food coloring to the water and mix in with a large spoon. 

6. Once the water is colored, the cardboard is in place, and you have your drawings ready, fill the left side of the tank with the cold, blue water.

7. Now, fill the right side of the tank with the hot, red water.  

8. Remember, the blue water represents a cold air mass and the red water represents a warm air mass. 

9. Using the drawing labeled 0 minutes and the red and blue markers, sketch what the tank looks like right now. Do this quickly--it does not have to be perfect. 

10. Finally, carefully remove the cardboard from the tank and start your stopwatch. 

11. Using your pre-labeled drawings, sketch what the tank looks like at 1, 3, 5, 7, 10, and 15 minutes.