Thursday, September 1, 2016

Making Fetch Happen

What's with the clouds? I'm sure many are wondering why we have so many clouds in just the eastern half of the Stateline, while our western counties have sunshine and clear skies.

The fault falls on Lake Michigan and a northeast wind over the lake. The cloud cover is actually lake-effect cloud cover, and will also bring a few showers to the Chicago area, but should miss the Stateline.

A second surge of cooler air this morning is passing over a warm Lake Michigan, water temperatures around 75°. This creates enough Delta T, or change in temperature to generate instability. This, along with some low level moisture, and converging winds all come together to generate upward vertical motion. As these come together they generate a few showers and the cloud cover as well.

There is also a large lake-fetch  - the final component to the equation. Fetch is most easily described as the length of the lake winds pass over. Today our NNE wind is entering the lake at the northern tip, and then exiting over the SE corner of the lake. This makes for a large lake fetch - and more instability is generated as the cooler air passes over the warm water.

Rain showers will stay east, but we are seeing the cloud cover from the lake effect process. Good news, the clouds won't last all day, by the early afternoon we will see more sunshine. Even with the sunshine it will feel fall like with high temperatures today in the low 70's and breezy, at times, north northeast winds.

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