Plenty of rain fell Monday across the Stateline with many locations recorded upwards of 2-4" of rain. Some of those locations include Dixon, Sterling, Rockford, Belvidere, Genoa, and Kirkland. Many other areas saw moderate to heavy rain, but the rain totals weren't as extreme. Flash flooding was also reported in downtown Rockford, Dixon, and Belvidere as a result of the intensity of the rain. The reasoning behind the storms dumping copious amounts of rain is the fact that we had ample heat and moisture available. Precipitable water is a tool we use to analyze how much moisture is in the atmosphere. When those values exceed 1.5", heavy rain is a distinct possibility. Monday we had totals of 2". As a result, the atmosphere was prime for heavy rain. In addition, the storms didn't move much at all due to a lack of upper-level winds. There was nothing in place to push the storms along, which led to flooding in portions of the region.
A cold front will swing through Tuesday evening. Ahead of that will again exist an air mass supportive of isolated thunderstorms and heavy rainfall. Once that front passes Tuesday evening, much cooler and drier air will filter into the area. Temperatures by Wednesday will be in the 70's for highs, and likely won't exceed 80° until possibly Sunday. Overnight lows will return to the 50's, and humidity values will be very low, making it feel more like fall as the calendar flips to September later this week!