Thursday will be a toasty one around the central Midwest. With a strong low pressure entering NW Iowa, a stiff southerly wind, and sunshine in a capped atmosphere, temperatures will close in on 90 degrees. Here's the surface map at 4:00pm.
Here's the projected 4pm temperatures.
Dew points are high by September 20th standards making it feel even warmer.
The warmth and moisture will generate plenty of instability with CAPE (convective available potential energy) over 4,000 j/kg in spots.
With strong dynamics and high instability strong thunderstorms are possible late in the day and into the evening ahead of the cold front and triple point. The Storm Prediction Center has an enhanced risk of severe weather in place over parts of Minnesota, Wisconsin, and Iowa.
The threat of a late season tornadoes exists over southern Minnesota and SW Wisconsin. Here's the significant tornado index which looks darn impressive for late September.
Storms are not expected in my area until evening at the earliest as a strong cap prohibits initiation until the front approaches. However, the cap does break out west in the evening allowing a squall line to sweep across much of SE Minnesota, Wisconsin, and Iowa until it weakens and dies as it approaches the Mississippi River (and western Illinois around 2-3:00 am). You can see the line explode to life around 4pm and then diminish as heating diminishes after sunset. Any severe weather in my area looks confined to gusty winds.
Behind the frontal passage much colder air will enter the entire Midwest Friday. Steady or falling temperatures are likely as stiff NW winds drive the cold air southeast. By Saturday morning winds will quickly diminish and temperatures tumble. The growing season could easily come to an end in NC Wisconsin where frost and lows in the mid 20s are shown.
Lows in my area should end up well into the 40s Saturday morning with a few valley locations in NE Iowa and SW Wisconsin inching into the upper 30s. Saturday should turn out to be a fine day as fall officially arrives to sunshine and crisp conditions. Enjoy the warmth of Thursday fans of summer, it may be 7 or 8 months before we see temperatures this warm again. Roll weather...TS