One thing that jumps out at me this time of the year is the fact that low pressure systems start getting large and stronger. The cloud and rain shields with them often stretch over 1000 miles as the jet streams get more intense allowing for huge circulations. A case in point is the current system moving through. It will be producing a nice soaking rain all the way from the Gulf of Mexico north into Canada.
The center of the low pressure Wednesday evening was over northwest Minnesota. On the surface map from 4 p.m. Wednesday below you’ll notice how the wind barbs converge toward the center of the low north of Bemidji.
There was a long cold front arcing southeast from the low pressure down into Wisconsin and all the way down the Mississippi River Valley. Another feature of autumn storms is often a big temperature contrast. Readings were in the 70s in Michigan, but only in the 30s and 40s in North Dakota behind the low pressure.
One large band of rain and thunderstorms was forming ahead of the cold front and sweeping northeast up from Missouri and Illinois into Wisconsin. This will be the band that focuses moderate rain over the eastern half of Wisconsin Wednesday night. As you’ll notice from the rainfall projection below, the heaviest is expected to fall east of a line from Eagle River to Clintonville, down to Milwaukee with 1.0″+ amounts possible. Then there is a relative dry slot curling up from Kansas to much of Minnesota to far western Wisconsin. Finally heavy moisture is wrapping around the northwest side of the low pressure and that could soak North Dakota and northwest Minnesota with close to 1.0″ of rain as well. The pattern forms the class “comma” shaped storm we normally see numerous times in the fall through spring around here.
Don’t expect this storm to move away in a hurry as it will be removed from the main steering currents for about 36 hours. It will sit and swirl across Wisconsin basically through Friday night before slowly pushing eastward. I guess when the storms get this big they can move just as slow as they want. While the dreary skies won’t be the greatest to look at, the conditions causing them is always interesting to watch come together. Until next time, hope you enjoy yourself!
This post was written by Tony Schumacher on October 17, 2012