textproduct: Chicago

KEY MESSAGES

- Brief chance (~30 percent) for a light wintry mix mainly north of I-88 tonight.

- Breezy/windy and warmer Wednesday.

- Mild with periods of showers and some storms Wednesday night into at least Friday, and again from later in the weekend into early next week.

DISCUSSION

Issued at 257 AM CDT Tue Apr 7 2026

Early morning surface analysis places 1034 mb high pressure across the upper Mississippi Valley. Breezy north-northeast low- level flow downstream of the center of the high was pulling colder air into the forecast area, with current temperatures generally in the low-mid 30s. The combination of somewhat breezy winds and patchy cloud cover (especially just inland of Lake Michigan across the Chicago metro area) has helped keep temps up a little from previous forecast, though no doubt we'll see some mid-upper 20s across far northern IL over the next few hours especially north of I-88 or so. This colder air mass is also quite dry, as noted by surface dew points in the teens (and even some single digits), which has limited the depth of lake- induced stratocu and greatly limited any snow shower potential. Can't rule out a flurry or two through this morning over/near the lake, but otherwise dry conditions are expected through at least early this evening. Winds will ease and gradually easterly with time this afternoon, but even with skies becoming mostly sunny will continue to support quite a range in our high temperatures today ranging from the mid-upper 30s near the lake shore to the mid-40s well west and south of the lake across interior northern IL/northwest IN.

Much farther to our northwest, GOES vapor imagery currently shows a deep mid-level short wave transiting the Canadian Rockies. As this feature propagates to the southeast across the lower Canadian prairies and our Northern Plains tonight, large scale height falls and resulting surface pressure falls will induce a south-southwesterly low-level jet from the Plains into the upper Midwest and western Lakes region tonight. Associated warm advection and isentropic upglide is progged to develop a narrow northwest to southeast oriented region of saturation later this evening and overnight, deepest across northwest and far northern IL. This narrow moist axis may produce a brief period of light precipitation as it lifts northeast across northern IL overnight. Model forecast thermodynamic profiles are initially cold enough for this to be in the form of light snow, though a warm nose develops around the 850 mb level in response to WAA which would likely support a very brief period of sleet/rain before precip ends. Thankfully, surface temperatures will also be warming slowly toward the freezing mark especially after midnight, which along with the expected brief duration of precip looks to limit the duration of any light freezing rain in any one place. Guidance is not to excited about QPF, and pops top out around 30 percent with areas mainly north of I-88 most likely to see this short period of light precip overnight.

The aforementioned surface low is progged to track south of Lake Winnipeg and toward the north shore of Lake Superior through Wednesday. Breezy southwest surface winds should develop as the surface gradient tightens, and will likely gust to 30+ mph by afternoon. Much warmer air will accompany the breezy conditions, with temperatures expected to surge into the mid- upper 60s across much of the area. Guidance indicates some degree of upper level cloud cover for much of the day, but if we were to see more sunshine we could potentially see both temperatures and winds overperform from current forecast and have nudged both a little higher than the NBM blended guidance. The surface low then passes north of Lake Superior Wednesday night and Thursday, trailing a cold front slowly into the forecast area. Shower chances ramp up within the narrow moist- axis ahead of the front Wednesday night. While some embedded thunder can't be ruled out, current guidance depicts fairly modest lapse rates/meager MUCAPE. The deep short wave passes well north of the area Thursday morning, and while showers are expected to continue along the front as it pushes slowly southeast during the day, forcing diminishes. A perusal of current global ensemble mean QPF for the 24 hours ending 00Z Friday (7 pm Thursday) is less than a half inch during this period.

The surface front, however, is progged to stall across or just south of the forecast area late Thursday, while another mid- level wave tracks across the upper Midwest Thursday night into early Friday. With moisture already in place, and additional moist advection wrapping north-northeastward from the western Gulf, this wave appears poised to bring another round of potentially heavier rain to the area - as indicated by an ensemble mean QPF axis of around 0.75" (individual operational runs indicate some 1.00"+ amounts, as well as greater MUCAPE values) across parts of the cwa by late Friday. While the actual frontal position is of somewhat low confidence in this time period, its general presence and the anticipated increase in cloud cover and rain also makes for lower temperature confidence. There could potentially be some large temp ranges Thursday and Friday, from the 50s/60s north of the front and near Lake Michigan to the 70s south of the boundary.

Extended global/ensemble guidance is in decent agreement for now with surface high pressure building across the Great Lakes region Friday night into Saturday, potentially pushing the frontal zone far enough south of the forecast area for a period of dry weather. Beyond that, models are depicting amplification of the upper pattern Sunday into Monday, as a long-wave upper trough develops over the west coast. This, in turn, induces a return of southwest low-level flow into the Midwest, with a renewed push of warm/moist air into the region along with the hint of several disturbances lifting into the the region from the base of the western trough. While confidence is low in the details at this distance, warmer and more active weather would be supported into early next week.

Ratzer

AVIATION /18Z TAFS THROUGH 00Z THURSDAY/

Issued at 1204 PM CDT Tue Apr 7 2026

Surface winds will continue turning easterly and eventually southeasterly as a high pressure system shifts eastward toward the northeastern United States.

Tonight, intermittent isentropic ascent may allow for a few snow or sleet showers to move over the terminals (looking at the 06-12Z window). At this point, we continue to favor a dry forecast (only a 20 to 30% chance of measurable precipitation). However, the introduction of targeted TEMPO groups may become warranted as trends evolve tonight.

Tomorrow, surface winds will trend southwesterly in advance of a cold front. Mixing profiles suggest frequent gusts of 30-35kt are likely during the afternoon hours (if not higher if mixing is especially efficient).

Borchardt

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 1 PM CDT this afternoon for the IL nearshore waters.

Small Craft Advisory until 4 PM CDT this afternoon for the IN nearshore waters.