Air Masses, Storms
and other scary stuff
and other scary stuff
Formation of Precipitation:
The Bergeron Process
The Collision-coalescence process
Some Different Forms of Precipitation
• Rain
– Drizzle vs. showers
Some Different Forms of
Precipitation
• Snow
• Sleet
• Glaze (ice storm)

6
Hail
The Formation of Hail
Global Precipitation
Global Precipitation:
The ITCZ Connection
Precipitation in the U.S.
What Is An Air Mass?
A

large parcel of air with
characteristics which distinguish
it from surrounding air
1000

mi (160...
Source Regions
 Extensive,

physically uniform surface area

 High

or low latitude
Not found in the midlatitudes (too ...
Air Mass Movement & Modification
 Once

an air mass
moves, it influences the
regions it enters
 It is also influenced by...
Lake-effect snow:
cP air crossing warmer water
cP air crossing warmer water
Areas commonly affected
around the Great Lakes...
Air Mass Classification
 Latitude

A = arctic/antarctic
P = polar
T = tropical
E = equatorial
 Surface Conditions
m = ma...
Major Air Mass Source Regions
 (c)A
 mP
 cP
 mT
 cT
 (m)E
Air Masses of North America
So what happens when these
air masses meet???
They start frontin’.
Frontal lifting
Movement of a Warm Front
Warm Front: Development
Movement of a Cold Front
Cold Front: Development
Comparison: Note the shape
of the frontal boundary
Stationary Front
Occluded Front
Fronts on a Weather Map
Putting it together:
Note line A – A’
A cross section along line A – A’
(from the map on the previous slide)
Real-World Application:
An Atlantic Storm
Life-cycle of a Midlatitude Cyclone
A Hypothetical Weather Map
(note the alternating Highs and Lows…)
How do the
Upper-level Winds Move?
Major Midlatitude Disturbances
 Midlatitudes
Where

are the most dynamic weather region

polar and tropical air masses m...
Characteristic weather changes
with the passage of a cold front:
 Sharp

temp. drop as the front approaches
 As the fron...
Mapping it out:
Midlatitude Anticyclones
 High

pressure systems moving west to east
 No fronts
 Subsidence
 Clear, dry weather
 Cold...
Now on to the fun stuff!
Lightning
Thunder
Tornadoes
Tornado formation
46
48
Tropical Disturbances
 Tropical

Depression - winds up to 38 mph
 Tropical Storm
- winds 39 - 73 mph
 Hurricane
- winds...
Hurricanes
Four different names
for the same event:






Hurricane
Typhoon
Cyclones, tropical
cyclones
Baguios
Hurricane Origins










Form in tropical and subtropical zones approx. 8° to 15° N or S
latitude
Rarely form ...
Hurricanes
Hurricane Tracking
Pressure Signature of a Hurricane
Hurricane Structure
Hurricane Katrina making landfall
Storm Surge
Storm surge damage in Galveston, TX from Hurricane Ike
(Category 2)
58
GEOG 100 Lecture 8--Precipitation, Air Masses and Storms
GEOG 100 Lecture 8--Precipitation, Air Masses and Storms
GEOG 100 Lecture 8--Precipitation, Air Masses and Storms
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GEOG 100 Lecture 8--Precipitation, Air Masses and Storms

  1. 1. Air Masses, Storms and other scary stuff and other scary stuff
  2. 2. Formation of Precipitation: The Bergeron Process
  3. 3. The Collision-coalescence process
  4. 4. Some Different Forms of Precipitation • Rain – Drizzle vs. showers
  5. 5. Some Different Forms of Precipitation • Snow • Sleet • Glaze (ice storm) 6
  6. 6. Hail
  7. 7. The Formation of Hail
  8. 8. Global Precipitation
  9. 9. Global Precipitation: The ITCZ Connection
  10. 10. Precipitation in the U.S.
  11. 11. 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  Source region: Where an air mass originates 12
  12. 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)
  13. 13. Air Mass Movement & Modification  Once an air mass moves, it influences the regions it enters  It is also influenced by those regions, especially in its lower section, closest to the ground
  14. 14. Lake-effect snow: cP air crossing warmer water 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 16
  15. 15. Air Mass Classification  Latitude A = arctic/antarctic P = polar T = tropical E = equatorial  Surface Conditions m = maritime c = continental
  16. 16. Major Air Mass Source Regions  (c)A  mP  cP  mT  cT  (m)E
  17. 17. Air Masses of North America
  18. 18. So what happens when these air masses meet??? They start frontin’.
  19. 19. Frontal lifting
  20. 20. Movement of a Warm Front
  21. 21. Warm Front: Development
  22. 22. Movement of a Cold Front
  23. 23. Cold Front: Development
  24. 24. Comparison: Note the shape of the frontal boundary
  25. 25. Stationary Front
  26. 26. Occluded Front
  27. 27. Fronts on a Weather Map
  28. 28. Putting it together: Note line A – A’
  29. 29. A cross section along line A – A’ (from the map on the previous slide)
  30. 30. Real-World Application: An Atlantic Storm
  31. 31. Life-cycle of a Midlatitude Cyclone
  32. 32. A Hypothetical Weather Map (note the alternating Highs and Lows…)
  33. 33. How do the Upper-level Winds Move?
  34. 34. Major Midlatitude Disturbances  Midlatitudes Where are the most dynamic weather region 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)
  35. 35. 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
  36. 36. Mapping it out:
  37. 37. 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
  38. 38. Now on to the fun stuff!
  39. 39. Lightning
  40. 40. Thunder
  41. 41. Tornadoes
  42. 42. Tornado formation
  43. 43. 46
  44. 44. 48
  45. 45. Tropical Disturbances  Tropical Depression - winds up to 38 mph  Tropical Storm - winds 39 - 73 mph  Hurricane - winds 74+ mph
  46. 46. Hurricanes Four different names for the same event:     Hurricane Typhoon Cyclones, tropical cyclones Baguios
  47. 47. 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
  48. 48. Hurricanes
  49. 49. Hurricane Tracking
  50. 50. Pressure Signature of a Hurricane
  51. 51. Hurricane Structure
  52. 52. Hurricane Katrina making landfall
  53. 53. Storm Surge
  54. 54. Storm surge damage in Galveston, TX from Hurricane Ike (Category 2) 58

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