1. Air Masses and Weather Fronts

2. 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?

3. 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.

4. 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 .

5. This means there are 4 combinations: What do you think they will be? Maritime tropical = wet & warm Continental tropical = dry & warm Maritime polar = wet & cold Continental polar = dry & cold Our weather constantly changes because different kinds of air masses are being pushed around the Earth.

8. In the USA, the jet stream push air masses from west to east. Therefore our weather generally comes from the west toward Georgia.

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

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

14. Cold front 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! .

15. Notice the kinds of clouds at a cold front.

17. Cold front Drier, cooler air mass

19. 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.

20. Notice the kinds of clouds at a warm front.

21. 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.

24. The weather remains the same until a force makes them move.

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

26. So what does the H and L mean on a weather map?

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

29. Kinds of weather maps.

31. Wind map

32. Combination map used for TV and internet

33. Another combination map – Can you read it?

34. Humidity map

35. Questions ? ?