Waves of widespread rain likely over the next few days

 While the Stateline remained dry throughout Saturday, our next wave of widespread rain is on the way overnight. Light rain was already falling across portions of Iowa at 6:30PM Saturday. Much of the local area in Northern Illinois and Southern Wisconsin will remain dry through Sunday morning, however.

The initial wave of rain will arrive early Sunday morning, providing light to steady rain showers for far NW Illinois and SW Wisconsin by 6AM. Rain will continue to spread East through the morning hours, eventually reaching areas along and East of I-39 by midday. Light to steady rain showers then continue through 7PM or so before the first lull in precipitation arrives. Total rainfall from this wave may exceed 1" for those West of I-39.

 

The second period of steady rain will begin Sunday night into Monday morning, with some embedded storms also possible in Central and Northeastern Illinois. Another lull in precipitation intensity and coverage will arrive for the afternoon, but early Monday evening is when the heaviest wave of rain arrives. This wave will have a very narrow band of heavy rainfall, oriented SW to NE. This band will slowly creep Eastward through the evening and overnight, before clearing the area Tuesday morning. Light rain persists into Tuesday afternoon and evening, before exiting completely by Tuesday night. Depending on where the narrow band mentioned above sets up, some locations may see more than 2" of rainfall from this wave.

 

In total, a broad area covering the entire Stateline should receive anywhere from 1.5-3.0" of rainfall. Notice however, that narrow bands of higher totals may set up within that broad region. Highest totals where heavy rain stalls out over a single area for multiple hours on end may receive upwards of 4" or more of rainfall. It is hard to pinpoint exactly where this axis of very heavy rainfall will set up, but model guidance is favoring NW Illinois (Northwest of line from Janesville to Freeport to Sterling) for now.

Those who see the higher thresholds of rainfall (3-4" or more) may see a low-end flooding risk come to fruition. While the ongoing dry and drought conditions will allow for a lot of rain to soak into the ground before flooding occurs, the narrow band Monday night into Tuesday morning may overcome that to produce some flooding concerns. The Weather Prediction Center placed the Stateline under a "Slight Risk" for excessive rainfall Monday into Tuesday. Put plainly, that translates to a 15% chance to see rainfall reach flash flooding guidance.

One way to counter the flooding concerns will be to keep street drains clear of recent leaves that have fallen off the trees. This will allow for water to drain quicker into the sewer system and keep it off the roadways and driveways.