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We know that rising air cools at DALR/SALR
Air mass: large region of air with uniform temperature and humidity
Fronts: boundary between 2 air masses
Types of air masses:
Very cold – Arctic (A)
Cool – Polar (P)
Warm – Tropical (T)
Wet – Maritime (m)
Dry – Continental (c)
All of these can be combined to form the five types of air masses:
mP, mT, cA, cP, cT
We usually don’t get arctic air masses that are very humid that is why mA
does not exist.
Source regions: typical foundation areas – masses that form over the oceans tend
to have more moisture than masses that form over land
Example is the subtropical highs and subpolar low
As they move they acquire surface characteristics. They also force away whatever
air mass was in their way.
Fronts: boundary between air masses and is the leading edge of the temperature and
Fronts are named based on the air mass behind it.
Types of fronts:
Cold – (blue triangles) advancing cold air rapidly and strongly pushes
warm air upward. As the cold air moves in it digs under the warm air and
pushes it upward. This is a great location for clouds, precipitation, and
possibly severe weather. Precipitation is usually heavy but brief.
Warm – (red semi-circles) advancing warm air. The warm air gently rises
over the cold air mass, which is not as strong as the cold front. Results in
light and steady rainfall. Clouds take up more space and have more aerial
Overrunning: process of warm air gently rising over a cold air
mass. This also causes inversions – freezing rain happens in the
wintertime during a warm front.
Stationary – (alternating blue triangles and read semi-circles) the boundary
where there is a cold air mass and a warm air mass but they are not going
into each other. They are either running parallel to each other or they are
not moving at all. There will always be large temperature differences on
either side of the front. This results in some precipitation and clouds and
looks like a warm front.
Zone of transition – more gradual transition than a cold front
Occluded – (purple) two cold air masses “close off” the warm air mass in
between them. It happens when there is a very large low-pressure system.
The cold front “catches” the warm front.
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Dry Line – (red hash mark) usually in the south central US. Not really
associated with air masses. Stationary conditions but there are no
temperature differences but big moisture differences. A boundary between
two air masses with similar temperature but different humidities. This is a
good place to get thunderstorms in the spring and summertime – this is the
reason for severe weather in the mid west.
Stages of Mid-Latitude Cyclones
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This note was uploaded on 10/11/2011 for the course PSYC, PSYC 2076, 2060 taught by Professor Briganti,gustan,perlis,namikas,wheeler during the Spring '10 term at LSU.