Hope you all are enjoying this pleasant cool-down this weekend. Looks as though the below-normal temperatures will continue for the eastern half of the U.S. and possibly even go cooler by next weekend after a wave of thunderstorms.
12Z NAM model guidance is suggesting an upper level shortwave with an associated surface cyclone moving through the IL/IN area on Monday 8/13, bringing some risk for severe weather with it. This severe threat will likely be in the form of a multicell/line structure initiating along a surface cold front, with hail and strong winds being the main hazards. Following the passage of this system, cooler temperatures will be maintained throughout the Great Lakes region, with little to no precipitation through Wednesday
Thursday (8/16), Latest GFS model output shows a stronger and more broad upper level trough amplifying southward from Canada into the Great Lakes region.
Accompanying this upper level trough will be a strong cold front extending from Quebec, across the Great Lakes, and through the central Plains. Ahead of this cold front will be quite moist air, with precipitatable water values(amount of water in the column of air if all liquid fell as precipitation) upwards of 2.2 inches as shown below. With this amount of moisture, thunderstorms and potentially heavy rainfall can be expected across the Great Lakes and central Plains on Thursday and Friday as the cold front moves eastward.
Behind this cold front will be more unseasonably cool air likely similar or even chillier than the temperatures this weekend. Here’s a look at 500 hPa height and surface temperature anomalies, giving us an idea of how cool this air will be:
As a result, most areas around the Great Lakes can expect high temperatures on Saturday and Sunday in the low 70s, with lows in the low 50s.