Update 12:15PM CST…
The National Storm Prediction Center has upgraded the severe weather outlook for the Chicago area – check the updated map which shows the portion of the Chicago area along and south of Interstate-80 now in the Enhanced Risk for severe storms (tan-shaded area depicting a 30% chance of severe storms within 25 miles of a given location), while the Chicago area north of Interstate-80 to the Illinois-Wisconsin state line and farther north into Wisconsin in the Slight Risk (yellow-shaded area depicting a 15% chance of severe storms within 25 miles of a given location.
Golf ball-sized hail will be possible in strongest storms from mid-afternoon on into the overnight hours. The greatest risk of tornadoes will be early to mid-evening (6pm-9pm), with the threat of damaging winds continuing well into the overnight hours. Localized flash-flooding is also possible with an inch or more rainfall in less than an hour occurring in some storms. Advance warning-time will be shortened considerably due to very fast movement of the storms – 65 miles per hour out of the south-southwest, and the fact that much of the potential storm activity may occur at night.
CHICAGO — The National Storm Prediction Center has positioned the entire Chicago area (northern Illinois into northwest Indiana) under a risk of severe thunderstorms later this afternoon and tonight. The greater Enhanced Risk (tan-shaded area on the severe weather outlook map depicting a 30% chance of severe storms within 25 miles of a given location) is south of Interstate-80 with the area north of Interstate-80 in a Slight Risk (yellow-shaded area on the severe weather outlook map depicting a 15% chance of severe thunderstorms within 25 miles of a given location). A lesser Marginal Risk (green-shaded area exists closer to the Illinois-Wisconsin state line into southern Wisconsin. Note the immense extent of the central United States under this very unusual late-winter severe storm risk area that extends from northeastern Texas into Lower Michigan.
As a warm front works its way north through our area today a few showers and thunderstorms could develop along that frontal boundary. The main threat for severe storms will occur as the center of intensifying low pressure tracks east out of Iowa today passing over northern Illinois later this evening – the associated very strong cold front moving through our area from west to east. Ahead of the system warm moist high-dewpoint air will flow into Illinois and Indiana on the nose of a destabilizing low-level wind jet, creating a environment ripe for the development of severe thunderstorm squall lines that may produce damaging winds, large hail, and a few tornadoes.
Be alert to advisory releases, monitoring weather radar and developments to our west, especially later this afternoon into the overnight hours as this very dangerous storm system evolves and moves through our area.