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 /06Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 1226 AM CDT Tue Apr 7 2026

Key Aviation Messages for the current TAF period:

- Lingering MVFR cigs and breezy northeast winds through 09Z around Chicago terminals

- Northeast winds becoming easterly, then eventually southeast after 06Z

- Less than a 30 percent chance for precipitation overnight into Wednesday morning

Winds have turned to the northeast across the forecast area. Breezier winds remain closer to Lake Michigan where a localized MVFR cloud deck remains parked over the city. Low confidence on exact timing, but winds are expected to gradually diminish and the lower clouds should scatter out in the next few hours.

VFR conditions are expected through Tuesday as winds turn to the east. As a surface ridge gradually drifts eastward, winds will gradually turn to the southeast (in the afternoon closer to KRFD and after 06Z for Chicago terminals). A weak embedded wave is expected to pass over northern Illinois which may include the chances for precipitation tonight. However, confidence is low on the details due to models disagreement on the strength of the forcing, the exact track of the wave, and low level temperatures. Since the chances for precipitation after 06Z remain less than 30 percent, it was decided to keep the TAFs dry at the moment (although the better chances may be closer to KRFD, which is outside its' current TAF window). In terms of precipitation type with this wave, temperatures are going to start out cold enough for snow tomorrow night. Warm air advection into the region will help turn snow over to rain and potentially even have a short window of some wintry mix (sleet and/or freezing rain). Any snow accumulations (IF they occur) would be nothing more than a dusting.

DK

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.