You'll forget we're starting August, and not October this afternoon with a bit of a chill in the air. High temperatures this afternoon will climb into the upper 60's to near 70°. Our average high for the beginning of August is 83° but today's high will be more typical of the 30th of September.
Northwest will increase in response to a tight pressure gradient as the strong departing low pressure currently sits over northern Lake Michigan, and high pressure moves over the Plains. In response stronger winds are generated which help to draw in the cooler air from the north.
Today will be the coolest out of the next seven days, but most of the next week ahead will be below average.
But it won't just be the Stateline that will notice the cooler start to August, most of the country will. The Climate Prediction Center outlook shows most of the country with below average temperatures through the 13th of August. The highest probability for below average temperatures will be centered in the Plains, but the Midwest is also in a high probability shade for below normal temperatures.
Only part of the country feeling the heat will be the Pacific Northwest, with high probabilities for above average temperatures through the middle of the month. The past week for them has been record setting with high heat, and even wildfires for some in that area.