Download Norwegian Model of Low-Pressure System

Norwegian Model of Low-Pressure System
n
sio
lu
cc
O
Cold air
Cold air
nt
Co
1 When conditions are favorable,
surface air pressure at the polar
front drops and a wave forms on
the front. The pressure is lowest at
the peak of the wave.
ld
Co
f
Warm air
2 In the Northern Hemisphere, winds
blow counterclockwise around the
low. As the central pressure
continues to drop, warm tropical
air on the east side moves
northward, and cold polar air on
the west side moves southward.
Warm air
Cool air
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fron
ro
Warm air
fro
nt
rm
Wa
W
ar
m
nt
Low
fro
on
Fr
l wave
ta
ld
Cold air
3 The quicker-moving cold front
eventually catches up to the warm
front, resulting in an occluded
front. The storm is most intense at
this stage. Eventually, the system
loses energy and begins to weaken.
It generally takes 12 to 24 hours for a low-pressure system to pass through
the first two stages shown above. After reaching the occluded stage, the low
can last for three days or more. Although the original low usually weakens
during the occluded stage, meteorologists must continue to monitor the
system, since the low can still be strong, with high winds and rains.
Sometimes a new low will develop where the cold, warm, and occluded
fronts meet.
Not all lows are like the simple one shown in the diagram. Some are
associated with more than two fronts, while others are associated with only
one front. Yet if you read weather maps over a period of time, you will
notice that many low-pressure systems follow a life cycle similar to the one
described by the Norwegian model.
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Unit 5 Atmosphere and Weather