textproduct: Chicago

KEY MESSAGES

- Periods of rain, possibly heavy, late Friday afternoon into Saturday morning, with possible localized flooding south of I-80.

DISCUSSION

Issued at 319 PM CDT Wed Apr 2 2025

Through Friday Afternoon:

The threat of showers and thunderstorms will come to an end from west to east following a cold frontal passage this evening. For more on the ongoing threat for severe thunderstorms, reference the meso discussions above.

Meanwhile, the threat of strong southerly wind gusts up to 45 mph will continue in the going wind advisory through early this evening. Accordingly, no changes are planned to the wind advisory headline. The ongoing convection has acted to slow the northward progression of the warm front for the last few hours, and hence has kept the stronger southerly winds largely south of the area. This should change within the next couple of hours, however, as the warm front begins to surge northward in response to the parent surface low quickly shifting northward into the Upper Midwest. As it does so, expect the strong gusty southerly winds to develop across the advisory area. There could even end up being a short hour or two period early this evening where winds gust 40-45 mph in areas north of the going advisory (including the Chicago metro area) before the cold front shifts across the area. Also, expect temperatures to jump up into the 60s across much of northern IL for a period early this evening following the warm frontal passage.

Winds will turn westerly this evening following the quick eastward passage of the cold front. While wind speeds tonight in the wake of the cold front will not be nearly as strong as the southerly winds ahead of the front, gusty westerly winds up to around 30 mph are expected at times overnight into Thursday morning before gusts ease Thursday afternoon. Expect a seasonably mild day under mostly cloudy skies Thursday, with highs ranging from the upper 50s to the lower 60s.

The surface cold front that shifts across our area this evening will stall out across the Ohio Valley on Thursday into early Friday. This front will become the primary focus for several additional rounds of heavy rain producing showers and thunderstorms Thursday through Friday as deep Gulf moisture continually feeds into this frontal zone. Fortunately, a majority of this heavy rain is expected to fall south of our area across southern parts of IL and IN through Friday morning. Accordingly, most of our area is likely to remain dry Thursday through at least early Friday afternoon. The only exception being a low chance (20-30%) for a few light showers well south of I-80 Thursday afternoon and evening.

KJB

Friday Afternoon through Wednesday:

The threat for rain (and even some storms) will return to our area late Friday through Saturday. This as several low amplitude impulses begin to eject northeastward out of a potent mid/upper-level trough/low shifting across the Desert Southwest. Each impulse is expected to drive a wave of surface low pressure northeastward along the remnant frontal boundary to our south through the weekend. The first such wave will track into central parts of IN Friday night into early Saturday morning. As it does, it will aid in the northward push of moisture over the surface frontal boundary, thus supporting increasing rain (and perhaps a few embedded thunderstorms) chances across much of our area Friday afternoon into Saturday. Rain chances will peak in the 80 to 100% range areawide Friday night, though the heaviest rainfall (1"+) is currently favored to fall south of I-80 into Saturday morning.

Our next wave of low pressure is expected to track farther to our southeast late Saturday into early Sunday morning. It appears this wave may remain far enough to our southeast to keep the threat for the next wave of rain south and east of our area late Saturday into early Sunday. Accordingly, aside from some low chance PoPs into Sunday morning (mainly south of I-80), drier weather is favored for the end of the weekend.

Temperatures through the weekend will cool down as northerly flow dominates. Daytime highs will generally be in the lower 50s, though even cooler conditions in the lower to mid 40s can be expected near the lake due to the onshore wind component. A period of even colder (below average) weather is then likely to shift into the area for Monday as a stout northern stream trough digs in over the Great Lakes. High temperatures will likely remain in the lower 40s for Monday, and the potential exists for periods of snow showers during the day. Conditions should then gradually moderate into the middle of next week following the eastward passage of a surface high.

KJB

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/

Issued at 1230 AM CDT Thu Apr 3 2025

Forecast concerns include...

Gusty westerly winds through this afternoon. Wind shift to northeast this evening.

A cold front has shifted east of GYY early this morning and there may be a few sprinkles and brief mvfr cigs as it continues moving east. Otherwise, westerly winds gusting into the lower/ mid 20kt range will continue through mid afternoon and diminish with sunset. Winds will turn light northwest this evening and then shift to light northeast by mid evening.

Some mvfr level cloud cover may spread back across northwest IL and RFD by daybreak and persist through midday. Confidence is low and its also possible this cloud cover may lift to low vfr, 3-4kft by the time it arrives.

There is a chance for showers tonight that may spread as far north as GYY but the bulk of this activity is expected to stay south of the terminals and no mention with this forecast. cms

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until noon CDT today for the IL and IN nearshore waters.