Download Class #25: Friday, March 7

Class #26: Monday,
March 9
Clouds, fronts, precipitation
processes, upper-level waves,
and the extratropical cyclone
Class #26: Monday, March 9,
2009
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Early stages in the life cycle of
the extratropical cyclone
Class #26: Monday, March 9,
2009
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Later stages in the life cycle of
the extratropical cyclone
Class #26: Monday, March 9,
2009
3
Cross sections through an
extratropical cyclone
Class #26: Monday, March 9,
2009
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Class #26: Monday, March 9,
2009
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Class #26: Monday, March 9,
2009
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Class #26: Monday, March 9,
2009
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Class #26: Monday, March 9,
2009
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Class #26: Monday, March 9,
2009
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Class #26: Monday, March 9,
2009
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Vorticity or cyclonic spin when a
wave crosses mountains
Class #26: Monday, March 9,
2009
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Stretching vertically increases
the spin or vorticity
Class #26: Monday, March 9,
2009
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The cold, warm, and dry
conveyor belts
Class #26: Monday, March 9,
2009
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Strong winds descending in the
dry conveyor belt
Class #26: Monday, March 9,
2009
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Class #26: Monday, March 9,
2009
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Warm fronts
• Have a slope upward from the ground
inclined more towards the horizontal than
cold fronts
• Have weaker vertical motions than cold
fronts
• Have a special name for the upglide of
horizontal and vertical motion called
overrunning, warmer air over colder air
Class #26: Monday, March 9,
2009
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Class #26: Monday, March 9,
2009
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Real warm fronts
• The meteogram shows a warm frontal
passage at 1000 UTC
• Move at about half the speed of cold fronts
• Have a sequence of layer clouds
• Have the highest clouds well ahead of the
front at the surface
• Are very 3-dimensional
• Can stall, for example in mountains
Class #26: Monday, March 9,
2009
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Real warm fronts
• Can stall when the cold dense air is hard
to replace
• Can have broad bands of moderate
precipitation
• Can produce long periods of precipitation
when they stall
• Can produce frontal fog with evaporation
• Are associated with freezing rain and sleet
Class #26: Monday, March 9,
2009
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Stationary fronts (continued)
• Weather along a stationary front can
resemble a warm front
• Although the front is stationary at the
surface, strong winds aloft may blow
across the front aloft, causing overrunning
• Can have extended periods of cloudiness
and precipitation on the cold side of the
front.
• Can have a jet stream aloft
Class #26: Monday, March 9,
2009
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Occluded fronts
• Involve 3 air masses
– 2 polar air masses at the surface, usually mP
and cP
– 1 tropical air mass, mT that has been lifted
entirely off the surface, and is occluded or
hidden from the surface weather map
• Have weather like warm fronts where mP
air replaces cP air , and weather like cold
fronts where cP air replaces mP air.
Class #26: Monday, March 9,
2009
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Class #26: Monday, March 9,
2009
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