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Weather blog: What exactly is a pneumonia front?

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Posted at 3:04 PM, May 06, 2020
and last updated 2020-05-06 16:40:34-04

The first weekend of May brought great weather to Southeast Wisconsin. We enjoyed high temperatures in the 70s both Saturday and Sunday. Then, the bottom fell out with a major temperature drop Sunday evening. So what happened? A pneumonia front.

Now, you may be asking, "What is a pneumonia front?" Great question! A pneumonia front is a lake enhanced cold front that brings a dramatic drop in temperatures. Officially, to be deemed a pneumonia front, the temperature has to drop at least 16° in one hour.

Milwaukee outdid itself on Sunday, with a drop of 26° in one hour. You can see from the observation chart below, General Mitchell International Airport in Milwaukee went from 73° just before 6 pm, to 47° just before 7 pm.

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You can also see the change in wind direction noted in the observation. The wind went from a northwesterly to northeasterly during that time frame, the indication that the cold air was coming in from the lake.

At the TMJ4 studio, the temperature went from 75° at 6:10 pm, to 53° at 6:29 pm, a 22° drop in less than 20 minutes!

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The pneumonia fronts generally move from NE to SW, ushering in cold air. The cool down will begin at the lake shore and then move inland, where the drop in temperatures are usually less dramatic.

These lake enhanced fronts occur mainly in the spring or early in summer, when Lake Michigan water temperatures are still cool.
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