An unusually deep upper level system is forecast to move across the Midwest this week, helping to bring some much cooler weather for the middle of the week. The water vapor satellite image below indicates two upper level systems, one moving in from southern Canada, and another over Texas. The latter will be responsible for starting up some rains early Monday morning over south central Kentucky and then across the rest of the region Monday.
The southern Canada trough will strengthen as it moves into the Midwest Tuesday morning. The upper low over Texas will shift into the Deep South as it begins to merge into the stronger northern system. The combination of the two systems looks to bring plenty of rain near the area (the background colors in the image below).
The image below indicates how unusually strong this upper level system is. These plots are based on ensemble forecasts from the SREF (Short-Range Ensemble Forecast). The contour lines represent the ensemble's average for how high up in the atmosphere this trough is on Tuesday evening. The background colors indicate how much above/below (yellow/blue colors) normal these heights are. The purple in the image below, indicates this system is unusual for the middle of September.
(from Penn State meteorology)
Given that cold air will follow this system, you may ask, how cold will it get? Below is the forecast for low temperatures Wednesday morning as high pressure builds into the region behind the associated cold front. Readings in the 40s will be common, roughly 10-15 degrees below normal for this time of year.
To find out how cold it will get where you live, go to the upper left part of this web page, and type in your zip code or city and state to find the forecast tailored for your home town!