textproduct: Chicago

KEY MESSAGES

- Low (15-20%) 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 wintry mix Tuesday night, mainly near the IL-WI stateline.

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

DISCUSSION

Issued at 129 PM CDT Mon Apr 6 2026

A broad surface high continues to reside over the northern Plains and will be drifting southward into northern IL and northwest IN on Tuesday. Ahead of the high is a frontal boundary that is stretching from northeast IA to the eastern UP of MI. As the high begins to drift towards the area tonight, this frontal boundary will get forced southward and become enhanced by the cooler air of Lake Michigan. While the frontal boundary will not result in much impactful weather for most, there remains a signal for some isolated to widely scattered showers to develop near the lake this evening into early Tuesday morning. The reason is due to some modest lake induced instability that is forecast to materialize just ahead of the front. However, with the subsidence from the high expected to be increasing overnight there will likely be some competing factors and thus confidence on these showers remains low. Regardless, have opted to maintain a slight (15-20%) chance in the forecast for snow showers given that temperatures will be cooling into the mid to upper 20s overnight.

Heading into Tuesday, the surface high will be moving overhead resulting in mostly clear skies and dry conditions. Though with winds expected to be out of the east-northeast, cooler temperatures are forecast with highs in the mid-40s inland with readings only in the mid to upper 30s near the lake. Unfortunately the surface high will not hang out long as a weak shortwave will be ejecting out of the central Plains Tuesday night which will in turn push the high east of the area. Associated with this subtle shortwave will also be an area of precipitation that will be lifting northward on a mid-level frontal boundary Tuesday night. Given that moisture across northern IL and northwest IN looks to be somewhat limited, it appears that the coverage from any precipitation will be more scattered and mainly focused north of I-80. That said, as precipitation begins temperatures should be cold enough (in the upper 20s to lower 30s) for the precipitation to start off as snow but as the frontal zone lifts through, temperatures (both at the surface and aloft) should be slowly warming overnight and could result in a brief period of a wintry mix especially near the IL-WI line. With forecast soundings during the precipitation not showing a ton of mid-level warming it appears that the favored precipitation type would be snow with perhaps some sleet mixed in before things go over to rain but there is a 10-15% chance that some freezing rain could occur if mid-level temperatures warm enough. Regardless, the short duration and moderating temperatures should keep any snow or ice accumulation at a minimum so no impacts are expected.

Any precipitation Tuesday night should taper by daybreak Wednesday resulting in another dry day. Temperatures on Wednesday will also continue to warm with highs in the mid to upper 60s. Though winds on Wednesday will also be gusty out of the southwest with speeds peaking around 30-35 mph during the afternoon. In fact, if deeper mixing is achieved some locally higher gusts could even be seen.

While we enjoy another mild spring day on Wednesday, an upper low is forecast to be moving across the northern Plains towards the Great Lakes with its associated surface low. Attached to the low will be a cold front that will be stretching from WI to KS that will move into northern IL and eventually northwest IN Wednesday night. Initially some scattered showers (and perhaps even a couple of thunderstorms) should be ongoing along the front, but as the front moves into our area the drier air in place looks to cause the showers to become more isolated. Thus rain chances will actually be diminishing as the front progresses through the area. Since the front is forecast to stall overhead on Thursday it seems that the areas that miss out on rain Wednesday night will have a shot for it on Thursday. Furthermore, with the stout southwesterly flow pattern aloft. Given that convection often manipulates boundary positions and how poorly the courser global guidance handles this shift, confidence the exact timing and placement of the showers and storms this weekend is somewhat low. Nevertheless, ensemble guidance does suggest that some instability will materialize on Thursday and result in some scattered showers and thunderstorms especially across the southern half of the area. Though with the weaker shear profiles (around 30 kts) it appears that the threat for severe weather is low at this time.

This frontal boundary is not expected to move much Thursday night into Friday which looks to result in continuous rounds of showers and embedded thunderstorms. In fact, with storm motions currently forecast to be parallel to the frontal boundary conditions do look favorable for training convection which could result in localized threat for flash flooding, especially if storms overlap areas that saw heavy rainfall this past weekend. Outside of the rain, temperatures for Thursday and Friday look to remain seasonably warm with highs in the 60s to around 70 each day (warmest south of the aforementioned boundary).

As for the upcoming weekend, this frontal boundary is forecast to hang around the southern Great Lakes and Ohio River Valley regions through the weekend and will serve as the focus for additional period of showers and thunderstorms as several shortwaves are projected to traverse the southwest flow pattern aloft. Given that convection often manipulates boundary positions and how poorly the coarser global guidance handles this shift, confidence the exact timing and placement of the showers and storms this weekend is somewhat low. Nevertheless, ensemble guidance does suggest that most areas could see upwards of 1-2 inches of rainfall by the end of the weekend (30-40% chance). With the already swollen streams/rivers, this additional rainfall will likely keep the river flood threat around and could even result in some localized urban flooding as well.

Yack

AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 640 PM CDT Mon Apr 6 2026

Gusty northwest winds early this evening will turn northeast behind a backdoor cold front currently diving southeast across Lake Michigan. Latest timing of this boundary has it reaching ORD/MDW/GYY between ~1-2Z. Winds may gust to 20-25 kt for a few hours behind the front before gusts ease overnight. Winds then trend east through the day on Tuesday, remaining light.

A brief period of non-accumulating flurries can't be ruled out overnight tonight but the potential remains too low to include in the TAFs (<20% chance).

Petr

LOT WATCHES/WARNINGS/ADVISORIES

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

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