“Pneumonia Front” comes down Lake Michigan

Bill's Blog

During mid-late spring, shallow cold air can slide down Lake Michigan and result in some dramatic temperature drops. That was certainly the case yesterday in Chicago on Tuesday. We call this a “pneumonia front“. See the weather observations from the Harrison-Dever Crib from Tue. evening.

At 6 pm, the temperature at the Chicago Water Intake was 81.7°. Just one hour later, the temperature had fallen to 48.9°. That’s a drop of 33.7° in an hour! At 6 pm, he wind was SSW at 21.5 mph. One hour later, it was N at 17 mph, gusting to 24 mph. At 6 pm, the relative humidity was 45.1%. One hour later it was 100%. The dew point fell from 58.8° to 48.0°.

Record of Temperature at Dew Point

This is a record of the temperature and dew point from a private weather station (Patrick DeHaan – our GasBuddy). His office has a weather station in Chicago.

By the way, while the temperature had fallen into the 40s along the Chicago Lakeshore, the temperature at 8 pm at the South Haven, Michigan Lighthouse was 75.6°.

Weather Data from Tuesday Evening at Michigan City IN

At the beach at Michigan City, Indiana (data above)…the temperature fell from 77.7° at 9 pm to 49.6° at 11 pm.

I grew up in Evanston and Wilmette, Illinois and I remember some spectacular “pneumonia fronts”. They would occur from late April to early June. Once I remember playing golf at a small course in SE Wilmette on a sunny day that warmed to 85°. The front dropped the temp. to 50° in two hours and a layer of fog rolled in from off the lake.

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