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
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)
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
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)
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
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
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