As stated in the previous post, a potent fall storm is in the works for mid-week. The forecast is still on track for a low pressure system to move inland from the Pacific and track across the Rockies today. The low will deepen on the eastern side of the Rockies Tuesday, and then will eject into the plains Wednesday morning and afternoon.
The Storm Prediction Center has already issued an Enhanced Risk for strong to severe storms Wednesday afternoon including Kansas City, Mo, St. Louis, Mo, and Springfield, Il. A Slight Risk is issued as far north as the Quad Cities and Peoria. This area is highlighted for the greatest severe potential because of the position of the jet stream. With the exit region of the jet stream in this area, it brings strong diffluence( or divergence), strong mid-level lapse rates, and strong shear (winds changing direction with height). All of these are ingredients needed for strong storms. Biggest threats for those areas will be damaging wind gusts, hail, and isolated tornadoes.
Closer to the Stateline, the set up is different. The warm front will stay south of us through Wednesday afternoon. This will keep the storm potential down because we won't have as much moisture or lift to work with in peak storm hours. With limited energy and moisture to work with, Northern Illinois and Southern Wisconsin will mainly see rain showers, though some rumbles of thunder are possible. We look to pick up about a half inch to an inch of rainfall when its all said and done Thursday morning, though one thing we will keep an eye on is going to be the wind. Late Wednesday into Thursday winds will gust up to, and even over 40 mph, as there will be a large difference in pressure, and a big change in temperatures. These create strong gradients which translate to high winds. Wind whipped rain showers will be a concern Wednesday late afternoon and overnight, and is something we will continue to track.
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