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High/Low Pressure on Weather Maps

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ASK THE METEOROLOGIST

Sometimes I see low pressure depicted on a weather map where the lines of barometric pressure do not support that a low pressure area exists there. Does this mean that it is a high altitude low pressure area?

Lotus Moon Wolfe

Mount Shasta High School

 

This is very common. Although in our weathercasts lines of barometric pressure are not shown, sometimes the cloud patterns on the satellite and radar loop may not represent the high or low pressure system depicted. In fact, a similar situation is happening right now over the Pacific Northwest.

A large ridge of high pressure is the dominant weather feature impacting the entire West, meaning the jetstream is well to our north. However, underneath this high pressure air mass, a small area of counterclockwise rotation can be seen on the satellite & radar, a low pressure system. Because this disturbance is rather small, having little impact on the weather, and not a full representation of 1. The weather in place or over our region or 2. the jetstream pattern (this is known as a high pressure ridge), the low will not be drawn on the weather map.

So the answer to this question is yes, a column of air can have large pressure differences. A perfect example of this is a hurricane. A hurricane is a large body of low pressure that forms over water. But little people know that in the higher levels of the atmosphere, a high pressure air mass exists above this area of low pressure, and it’s also part of the hurricane!

Most areas of low pressure are areas of convergence, the air converges and rises …higher in the atmosphere (within the same column of air) the air eventually diverges, leading to high pressure formation and a clockwise rotation.

 

Meteorologist Alyssa Caroprese