Multiple rounds of heavy rainfall could bring a threat for flash flooding to the Stateline this weekend. The first round will arrive Saturday afternoon/evening, with the scattered storms continuing into Sunday. The slow motion of the thunderstorms through an abundantly moist air mass will allow for some torrential rain to fall in some spots, with rainfall rates possibly upwards of 1″ per hour or more.
We will likely be dry but humid to start off Saturday. Thunderstorm coverage will increase through the afternoon as the first round of storms dive South along an outflow boundary. Rainfall should begin by 5-6PM if not a little earlier for most in the Stateline.
Heavy rainfall will likely continue through the late evening and overnight, as forward motion of storms will be slow. This will allow for the heaviest rain to linger over some spots for longer, adding up rainfall totals much quicker.
The exact placement of the heaviest rainfall is still very uncertain at this time, but there is an increasing potential for 2″ of rain or more near and Northwest of Rockford. This will not be 2″ for everyone in those areas, but the highest chances for extremely heavy rainfall will be mostly centered across far NW Illinois and Southern Wisconsin through Monday morning.
The Weather Prediction Center has noticed an uptick in rainfall totals and issued a Moderate Risk (Level 3 out of 4) for excessive rain between Saturday and Sunday. This equates to a 40% chance for flash flooding guidance to be reached in the red contours. Those in the Moderate Risk could see potentially 2-5″ of rainfall through Monday…