An air mass is a large body of air with consistent temperature and moisture characteristics that behaves as a single unit. Air masses form over source regions and move across Earth's surface. When different air masses meet, fronts are formed which can produce stormy weather. Midlatitude cyclones develop along fronts between polar and tropical air masses. Characteristics like warm fronts, cold fronts, and occluded fronts determine the weather changes that occur. Hurricanes are intense tropical cyclones that form over warm ocean waters and derive energy from moisture and heat released by thunderstorms within the storm.

1. Air Masses, Storms
and other scary stuff

2. What Is An Air Mass?

3. What Is An Air Mass?
 A large parcel of air with
characteristics which distinguish
it from surrounding air

4. What Is An Air Mass?
 A large parcel of air with
characteristics which distinguish
it from surrounding air
1000 mi (1600 km) across, several
miles deep

5. What Is An Air Mass?
 A large parcel of air with
characteristics which distinguish
it from surrounding air
1000 mi (1600 km) across, several
miles deep
Conditions of temp., humidity,
stability consistent horizontally at
any altitude

6. What Is An Air Mass?
 A large parcel of air with
characteristics which distinguish
it from surrounding air
1000 mi (1600 km) across, several
miles deep
Conditions of temp., humidity,
stability consistent horizontally at
any altitude
Moves as a coherent whole, not
easily torn apart by local turbulence

7. What Is An Air Mass?
 A large parcel of air with
characteristics which distinguish
it from surrounding air
1000 mi (1600 km) across, several
miles deep
Conditions of temp., humidity,
stability consistent horizontally at
any altitude
Moves as a coherent whole, not
easily torn apart by local turbulence
 Sourceregion: Where an air
mass originates

8. Source Regions

9. Source Regions
 Extensive, physically uniform surface area

10. Source Regions
 Extensive, physically uniform surface area
 High or low latitude

11. Source Regions
 Extensive, physically uniform surface area
 High or low latitude
Not found in the midlatitudes (too much atmospheric
activity)

12. Source Regions
 Extensive, physically uniform surface area
 High or low latitude
Not found in the midlatitudes (too much atmospheric
activity)
 High pressure zones are common source regions
(because air sinks, stays close to the ground, where it
picks up surface characteristics)

14. Lake-effect snow:
cP air crossing warmer water
5

15. Lake-effect snow:
cP air crossing warmer water
Areas commonly affected
around the Great Lakes
5

16. Lake-effect snow:
cP air crossing warmer water
Areas commonly affected
around the Great Lakes
Buffalo, NY (Dec., 2001)--Nearly seven
feet of lake effect snow fell in 5 days
5

17. Air Mass Classification

18. Air Mass Classification
 Latitude
A = arctic/antarctic
P = polar
T = tropical
E = equatorial

19. Air Mass Classification
 Latitude
A = arctic/antarctic
P = polar
T = tropical
E = equatorial
 Surface Conditions
m = maritime
c = continental

20. Major Air Mass Source Regions

21. Major Air Mass Source Regions
 (c)A

22. Major Air Mass Source Regions
 (c)A
 mP

23. Major Air Mass Source Regions
 (c)A
 mP
 cP

24. Major Air Mass Source Regions
 (c)A
 mP
 cP
 mT

25. Major Air Mass Source Regions
 (c)A
 mP
 cP
 mT
 cT

26. Major Air Mass Source Regions
 (c)A
 mP
 cP
 mT
 cT
 (m)E

27. Air Masses of North America

28. So what happens when these air
masses meet???

29. So what happens when these air
masses meet???
They start frontin’.

30. Frontal lifting

31. Movement of a Warm Front

32. Warm Front: Development

33. Movement of a Cold Front

35. Cold Front: Development

36. Comparison: Note the shape
of the frontal boundary

37. Stationary Front

38. Occluded Front

39. Fronts on a Weather Map

40. Putting it together:
Note line A – A’

41. A cross section along line A – A’ (from
the map on the previous slide)

42. Real-World Application:
An Atlantic Storm

43. Life-cycle of a Midlatitude Cyclone

44. A Hypothetical Weather Map
(note the alternating Highs and Lows…)

45. How do the
Upper-level Winds Move?

46. Major Midlatitude Disturbances
 Midlatitudes are the most dynamic weather region
Where polar and tropical air masses meet and mix
 Midlatitude cyclones
(a.k.a. depressions, lows, wave cyclones)
Large low pressure systems (1000+ miles across)
moving from west to east in the region of the Westerlies
(35º to 70º N and S latitude)

47. Characteristic weather changes with
the passage of a cold front:

48. Characteristic weather changes with
the passage of a cold front:
 Sharp temp. drop as the front approaches

49. Characteristic weather changes with
the passage of a cold front:
 Sharp temp. drop as the front approaches
 As the front approaches, wind direction is southerly

50. Characteristic weather changes with
the passage of a cold front:
 Sharp temp. drop as the front approaches
 As the front approaches, wind direction is southerly
 After the front passes, wind shifts to more northerly
(opposite for the Southern Hemisphere)

51. Characteristic weather changes with
the passage of a cold front:
 Sharp temp. drop as the front approaches
 As the front approaches, wind direction is southerly
 After the front passes, wind shifts to more northerly
(opposite for the Southern Hemisphere)
 Air pressure drops as the front approaches, rises
after it passes

52. Characteristic weather changes with
the passage of a cold front:
 Sharp temp. drop as the front approaches
 As the front approaches, wind direction is southerly
 After the front passes, wind shifts to more northerly
(opposite for the Southern Hemisphere)
 Air pressure drops as the front approaches, rises
after it passes
 Clear skies, followed by clouds and precip. along
the edge of the front, then colder with clear skies
again as the front passes

53. Mapping it out:

54. Midlatitude Anticyclones
 High pressure systems moving west to east
 No fronts
 Subsidence
 Clear, dry weather
 Cold in winter
 May stagnate, stalling other weather
systems behind them

55. Now on to the fun stuff!

56. Lightning

57. Lightning

58. Lightning

59. Thunder

60. Tornadoes

61. Tornado formation

62. 35

63. 36

64. Tropical Disturbances
 Tropical Depression - winds up to 38 mph
 Tropical Storm - winds 39 - 73 mph
 Hurricane - winds 74+ mph

65. Hurricanes
Four different names
for the same event:
 Hurricane
 Typhoon
 Cyclones, tropical
cyclones
 Baguios

66. Hurricanes
Four different names
for the same event:
 Hurricane
 Typhoon
 Cyclones, tropical
cyclones
 Baguios

67. Hurricane Origins

68. Hurricane Origins
 Form in tropical and subtropical zones approx. 8° to 15° N or S
latitude

69. Hurricane Origins
 Form in tropical and subtropical zones approx. 8° to 15° N or S
latitude
 Rarely form within 3° N or S of equator (no Coriolis force), rarely
cross it

70. Hurricane Origins
 Form in tropical and subtropical zones approx. 8° to 15° N or S
latitude
 Rarely form within 3° N or S of equator (no Coriolis force), rarely
cross it
 Tend to form in or just poleward of the ITCZ

71. Hurricane Origins
 Form in tropical and subtropical zones approx. 8° to 15° N or S
latitude
 Rarely form within 3° N or S of equator (no Coriolis force), rarely
cross it
 Tend to form in or just poleward of the ITCZ
 Tend to form in late summer and fall (warmest sea sfc. temps.)

72. Hurricane Origins
 Form in tropical and subtropical zones approx. 8° to 15° N or S
latitude
 Rarely form within 3° N or S of equator (no Coriolis force), rarely
cross it
 Tend to form in or just poleward of the ITCZ
 Tend to form in late summer and fall (warmest sea sfc. temps.)
 Storm’s low pressure cell feeds off warm sea sfc. temps. (up to
81°F!)

73. Hurricane Origins
 Form in tropical and subtropical zones approx. 8° to 15° N or S
latitude
 Rarely form within 3° N or S of equator (no Coriolis force), rarely
cross it
 Tend to form in or just poleward of the ITCZ
 Tend to form in late summer and fall (warmest sea sfc. temps.)
 Storm’s low pressure cell feeds off warm sea sfc. temps. (up to
81°F!)
 Gains energy from release of latent heat of condensation during
intense precipitation

74. Hurricane Origins
 Form in tropical and subtropical zones approx. 8° to 15° N or S
latitude
 Rarely form within 3° N or S of equator (no Coriolis force), rarely
cross it
 Tend to form in or just poleward of the ITCZ
 Tend to form in late summer and fall (warmest sea sfc. temps.)
 Storm’s low pressure cell feeds off warm sea sfc. temps. (up to
81°F!)
 Gains energy from release of latent heat of condensation during
intense precipitation
 Always form over oceans

75. Hurricane Origins
 Form in tropical and subtropical zones approx. 8° to 15° N or S
latitude
 Rarely form within 3° N or S of equator (no Coriolis force), rarely
cross it
 Tend to form in or just poleward of the ITCZ
 Tend to form in late summer and fall (warmest sea sfc. temps.)
 Storm’s low pressure cell feeds off warm sea sfc. temps. (up to
81°F!)
 Gains energy from release of latent heat of condensation during
intense precipitation
 Always form over oceans
 Do not / rarely form in the south Atlantic or southeast Pacific
because the water is too cold and air pressure too high

76. Hurricane Origins
 Form in tropical and subtropical zones approx. 8° to 15° N or S
latitude
 Rarely form within 3° N or S of equator (no Coriolis force), rarely
cross it
 Tend to form in or just poleward of the ITCZ
 Tend to form in late summer and fall (warmest sea sfc. temps.)
 Storm’s low pressure cell feeds off warm sea sfc. temps. (up to
81°F!)
 Gains energy from release of latent heat of condensation during
intense precipitation
 Always form over oceans
 Do not / rarely form in the south Atlantic or southeast Pacific
because the water is too cold and air pressure too high
 Storm intensity lessens as it gains latitude (into cooler waters) or
moves over land

77. Hurricanes

78. Hurricane Tracking

79. Pressure Signature of a Hurricane

80. Hurricane Structure

81. Hurricane Katrina making landfall

82. Storm Surge