3 hour Pressure Falls
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With this map, you should be able to find the following:
- pressure tendencies
- frontal areas/movement
- areas of increased/decreased convergence
- Content
- Pressure Falls--Contoured (Isallobars)
- Green for black and white background maps (negative are dashed)
- Millibars over last three hours
- Positive numbers are pressure falls
Pressure falls are very important in short term forecasting. Radiosondes
are only sent up twice a day, thus everything else must come from
profilers, satellite, and surface data. Pressure falls are a result
of increased divergence aloft. If pressures are falling, the surface
flow will reflect that change and begin to flow towards that area...
hence increasing the convergence in that area and creating stronger
vertical motions. The pressure falls are a sign of what is going
on in the atmosphere above the surface. Without weather balloon data during the day, pressure
falls can be a good tool for figuring out what is going on overhead.
Trying to predict the future motions of a low pressure system are
made easier by contouring pressure falls (isallobars). Strong
pressure falls ahead of the center of low pressure show essentially where
the center of the low will be moving. Pressure rises should be shown in
the wake of the low pressure center after it moves on. Here is a
late December example.
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