Patchy Dense Fog early this Sunday morning – Heat Advisory southern sections and slight chance of strong thunderstorms north late afternoon/overnight

Temperatures and dew-points have come together allowing patches of dense fog to form early this Sunday morning across the Chicago area dropping visibility to near zero in some locations. A Dense Fog Advisory is in effect for much of the area west and south of Chicago until 9AM (gray-shaded counties on the headlined map). Visibility should rapidly improve by mid-morning. Check current local airport visibility on the map below.

Temperatures are forecast to rise into the lower 90s today and when combined with dew-points in the lower 70s will push heat indexes above 100-degrees this afternoon/early evening. Highest heat index values possibly exceeding 105-degrees are expected in counties south of Interstate-80 which have been placed under a Heat Advisory from Noon to 7PM CDT (orange-shaded counties on the headlined map).

Thunderstorms may develop over eastern Iowa into Wisconsin possibly spreading into northernmost counties of Illinois especially along the Illinois-Wisconsin state line later this afternoon and evening. Should these storms occur, a few may become strong to severe – the National Storm Prediction Center has the portion of Illinois generally along and north of Interstate-80 in a Marginal Risk of severe thunderstorms late this afternoon into the overnight hours (dark-green-shaded area on the severe weather outlook map below).

Because the air over the Chicago area is so moist, strongest thunderstorms could produce torrential downpours as well as damaging winds and hail – the National Weather Prediction Center has a portion of northern Illinois/northwest Indiana in a Marginal  Excessive Rainfall Outlook (green-shaded area on the third map below) with a greater risk of heavy downpours across Wisconsin.

Current airport visibility map…

Risk of severe thunderstorms today/tonight…

Risk of Excessive rainfall…

Day 1 Excessive Rainfall Forecast