Heat continues, strong threat of severe t-storms with excessive rainfall later

Update 9AM CDT…

The National Storm Prediction Center has upgraded Tuesday’s severe weather outlook – calling an Enhanced Risk area of severe storms over Wisconsin (tan-shaded area on the headlined map) extending south into the northernmost counties in Illinois. The Slight Risk of severe storms (yellow-shaded area on the headlined map) extends farther south into much of the Chicago area. 

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A third straight day with 90-degree high temperatures and heat indexes near 100-degrees is expected across the Chicago area Tuesday. Strong to severe thunderstorms are expected over western sections later this afternoon and continue overnight – damaging winds and large hail along with flooding downpours, especially during the overnight hours are likely.

Persons most susceptible to oppressive heat should take appropriate precautions today – stay in cool areas out of the sun, if at all possible. This will be the third consecutive day with heat indexes near 100-degrees, and we just experienced the second straight night with temperatures failing to drop below 75-degrees, giving little or no relief from the heat/humidity. The impacts of heat are accumulative, so Tuesday will be the most dangerous day in this current heat wave.

The National Storm Prediction Center has a good portion of the Chicago area in a Slight Risk of severe storms (yellow-shaded area on the headlined map), while the National Weather Prediction Center has the same area under a slight to Moderate Risk of Excessive rainfall (red and yellow-shaded area respectively on the map below).

The huge dome of hot and humid air remains over the Chicago area today – shifting east tonight, as a cold front slowly works its way out of Wisconsin and Iowa across northern Illinois. The cold front should move south and east of Chicago early Wednesday. An extended period of thunderstorms is expected – first reaching our westernmost locations later this afternoon with a very active overnight period punctuated with strong to severe storms and occasional heavy downpours. “Training” thunderstorms (storms continually passing over the same area) will likely cause rainfall totals in some spots exceeding 2 to 4-inches or more before the cold front finally moves out of our area Wednesday forenoon.

Excessive rainfall outlook Tuesday/Tuesday night…

Day 1 Excessive Rainfall Forecast