textproduct: Chicago

KEY MESSAGES

- Low (<30%) chance for scattered snow showers near Lake Michigan tonight into early Tuesday.

- Sub-freezing temperatures expected tonight, but warmer conditions develop Wednesday and into the weekend.

- Brief chance for a light snow/rain mix Tuesday night.

- Periods of showers and storms are possible late in the week into next weekend.

DISCUSSION

Issued at 239 AM CDT Mon Apr 6 2026

Early morning GOES vapor imagery shows a low-amplitude short wave tracking quickly east-southeast across the western Great Lakes region. At the surface, a cold frontal trough associated with this wave extended from central Lake Michigan, southwest into far southeastern IA as of 06Z. A cluster of showers (with a couple of isolated lightning strikes noted over the past 1-2 hours) was noted ahead of the cold front, from La Salle county to southern Lake Michigan and northwest Indiana. These showers will exit the forecast area to the east during the predawn hours, with the cold front following shortly behind them. Breezy northwest winds gusting around 30 mph will usher in slightly cooler temperatures today, resulting in highs from the mid-upper 40s along the IL/WI border to the mid-50s well south of I-80. Sky cover will vary from partly to mostly cloudy (more clouds likely north, more sun to the south).

Another sheared mid-level short wave is progged to transit the upper Midwest this afternoon, which will send another reinforcing, sharp lake-assisted cold front southward into the area this evening. This will turn still-blustery winds more north-northeast tonight, while also dropping temperatures into the mid-20s to low-30s. There also continues to be guidance support from high-res models for scattered snow showers along/behind the frontal zone late this evening into the overnight hours, with lake to 850 mb delta-Ts around 15/16C and equilibrium heights around 6 kft. This may support some scattered lake-induced snow showers overnight as the mid-level trough axis passes overhead. While blended pop guidance isn't too excited, did add some slight chance (~20%) pops over the lake and adjacent counties of northeast IL/northwest IN for the overnight hours as well as some patchy trace to 0.1 accumulation amounts. We'll have to keep an eye on trends later today/tonight in case these snow showers end up being more robust. Low-level winds ramp down quickly Tuesday morning as surface high pressure builds in from the northwest, though a weak convergence axis is progged to linger into the northwest IN shore during the morning, thus scattered snow showers would likely persist into early Tuesday there before dissipating.

Temperatures should fall off quickly Tuesday evening, dipping into the 20s again over far northeast IL (especially northern Chicago suburbs) as the center of the surface high shifts just to our east across the Great Lakes. Surface winds back south- southeast overnight however as the high drifts away, and warm advection flow ramps up downstream of an upper trough over the Plains. This, in addition to increasing cloud cover, should produce slowly rising temperatures into the low-mid 30s overnight. There also remains decent model and ensemble agreement in resulting moist isentropic ascent and frontogenetic forcing within the northward advancing mid-level baroclinic zone to result in development of light snow (potentially changing to rain as the column warms/moistens) overnight, primarily across the northwest half or so (generally northwest of the I-55 corridor). As the previous discussion indicated, NBM pops can be underdone in these lighter QPF scenarios, but did come in slightly higher than previous runs. Also can't rule out a brief period of freezing rain as the column warms, though surface temps will also be rising with time as well and expect any FZRA would be short-lived.

Any lingering precipitation should lift north of the cwa early Wednesday morning, with a dry, breezy (windy?) and much warmer day in store. NBM blended wind guidance currently tops out near 35 mph, though higher gusts around 40 mph would be possible if cloud cover clears out sufficiently in the afternoon. Current forecast highs in the mid-upper 60s could also be a little underdone if we were to mix more deeply with more sunshine.

Shower chances then return to the area Wednesday night and Thursday, as a deep upper trough lifts across the upper Midwest and trails a cold front into the region during the Thursday/Thursday night period. Can't rule out some embedded thunderstorms, though instability continues to look fairly muted within the relatively narrow moist axis ahead of the front, with guidance maintaining greater SB/MUCAPE values back across the Plains and lower Missouri Valley. Details remain somewhat unclear later in the forecast period, as surface high pressure eventually builds into the upper Midwest while the aforementioned cold front stalls across our south of our area. If the front stalls nearby, additional short waves transiting the baroclinic zone could support additional rounds of showers and possibly thunderstorms Friday into the weekend. If the high builds in more strongly, the front could end up far enough south of the forecast area for a period of dry weather early in the weekend. In either case, global ensembles continue to suggest an active weather pattern persists early next week.

Ratzer

AVIATION /06Z TAFS THROUGH 12Z TUESDAY/

Issued at 1242 AM CDT Mon Apr 6 2026

Key Aviation Messages for the current TAF period:

- Scattered showers (and any chance for MVFR cigs) are expected to be east of the terminals by 07Z.

- Gusty northwest winds are expected through the day today.

- Winds diminish and turn north-northeasterly at the end of the current TAF window

A band of showers is visible on the KLOT radar ahead of cold front moving across the airspace. Most cigs with these showers remain VFR, but there is a chance that localized MVFR cigs are possible during a shower. Regardless, these showers are expected to be east of the terminals by 07Z. Prevailing winds are currently out of the west, but a brief burst of 20 knot northwest wind gusts are possible as the showers pass through.

Winds are expected to turn to the northwest behind the front with intermittent gusts up to 20 knots in the cold air advection regime. A patch of MVFR cigs in northern Minnesota will be monitored through the night. There is still a non-zero chance that those lower cigs make there way into northern Illinois (best chances near KRFD and the state line), but for now was kept out of the TAF. After sunrise, deeper mixing will allow for more persistent gusts between 20 to 25 knots through the day. Otherwise, VFR and dry conditions are expected.

As surface high pressure expands over northern Wisconsin after 00Z tomorrow, a weak surface trough will exit the northern Great Lakes to the east. As this occurs, winds will gradually become more northerly and flip to the northeast closer to 06Z. There is a less than 30 percent chance for a brief shower (potentially some flurries) around 06Z as the trough moves east. However, the amount of dry air depicted in model soundings prohibit mention of any precip in the TAFs presently.

DK

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 11 AM this morning to 10 AM CDT Tuesday for the IL and IN nearshore waters.