1. What happens when air masses meet?

2. What is an air mass? Large volume of air with uniform temperature and humidity readings Gets its characteristics from where it forms Continental: forms over land (dry) Maritime: forms over water (moist) Tropical: forms near equator (warm) Polar: forms nearer poles (cold)

3. Continental Air Masses Polar (cP) Tropical (cT)

4. Maritime Air Masses Tropical (mT) Polar (mP)

9. What happens when different air masses meet? Boundary between two different air masses is a: FRONT

12. Types of Fronts Cold Front Warm Front Stationary Front Occluded Front

13. What happens in a cold front?

14. Cold air moves into warmer air

15. Cold Front Cold air moves in, replaces warm air Cold air is more dense than warm air Cold air pushes warm air up Tall clouds form (cumulus and cumulonimbus)

17. Clouds are right along the front Precipitation is brief, but heavy (thunderstorms) Band of precipitation 75 miles around front (about 50 miles ahead and 25 miles behind) (about 50 miles ahead and 25 miles behind)

18. 75 miles

19. Air pressure is lowest at front After front passes: colder air mass temperature drops temperature drops skies clear skies clear pressure increases pressure increases Cold fronts move faster than warm fronts (about 30 mph)

20. Weather map symbol

21. Warm air moving into cold Predictions?

22. Warm air moving in

23. What happens with a warm front? Warm air mass advances and replaces cold air mass Warm air is less dense than cold Warm air rides above the colder air

24. Warm Front

25. Clouds start to form 1000 miles ahead of the front Cirrus clouds develop, followed by lower level stratus clouds Belt of precipitation is about 300 miles wide (starting 100-400 miles ahead of the front)

26. 1000 miles

27. Rain (precipitation) is gentle, but may last for a long period (several hours or days) Weather changes slowly (front moves about 20 mph) Warmer air finally replaces the colder air

28. As the front passes: Temperature increases Skies clear Pressure increases

29. Weather map symbol

30. Fronts – boundary that separates 2 air masses with different temperatures

31. Clouds: altostratus Warm front

32. Cold Front

33. HINT: sudden burst of intense rain over a small area Cold Front

34. HINT: this is a squall line Cold front

35. Stratus clouds: warm front

36. Clouds on Monday Clouds on Tuesday Warm front

37. Another squall line: COLD FRONT Robin Brueckner 2004

38. HINT: low gray clouds, long period of light snow WARM FRONT!!!!!!!!

39. Cold Front

40. Cold front Sharp break between air masses

42. Stationary Front

43. A stationary front occurs when the air masses on either side of the front are not moving toward each other.

44. Stationary Front Neither air mass pushes into the other Generally causes unsettled conditions –Rain, clouds, etc… Flooding may occur if front does not pass

45. OCCLUDED FRONT Warm air mass gets caught between 2 colder air masses and is forced aloft

46. Formation of an Occluded Front

47. Occluded Front A cold air mass catches up to another cold air mass Warm air is ‘squeezed’ out in the middle Causes precipitation

51. Important Vocabulary Air mass – (cT, cP, mT, mP, cA) Front Warm front Cold front Occluded front Stationary front

52. Winds spiral clockwise out of the High and counterclockwise into the Low Fronts are low pressure – lousy weather After the front passes – happy weather

53. Weather in a High Clockwise Rotation Bright, Clear Happy Weather

56. Hurricanes – counterclockwise low pressure systems (lousy weather)