textproduct: Chicago

KEY MESSAGES

- Lake effect snow showers will meander across the northeastern Illinois and northwestern Indiana shores of Lake Michgian late this evening into early Wednesday AM, though accumulations should stay below an inch.

- Forecast high temperatures are above the freezing mark areawide by Friday, marking the end of a prolonged stretch of daily highs below 32 degrees.

- Periodic (mainly light) snow chances exist through the end of the week, with the highest chances (30-40%) Thursday night, potentially falling as a wintry mix. - A pattern change toward warmer temperatures (highs and lows both above freezing) may materialize by the middle of next week.

DISCUSSION

Issued at 316 PM CST Tue Feb 3 2026

Through Wednesday night:

After having cleared out earlier in the day, low stratus has begun marching inland across the Chicago metro and into northwest Indiana this afternoon. Expect this to continue expanding southward through the rest of the evening. Can't rule out occasional flurries beneath this cloud layer as well. Heading into the late evening and overnight period, weak convergence over the lake paired with saturation touching the DGZ may allow for a band of lake effect snow to develop and meander along the southern Lake Michigan shore through the night. Confidence in how far inland this reaches is on the lower side but can't rule out a localized dusting of snow (0.1 to locally 0.5") over parts of Cook, Lake (IN) and Porter Counties, highest near the lakeshore. Any lingering lake effect snow showers likely shift back out over the lake Wednesday morning. The rest of the day on Wednesday looks dry areawide with high temperatures still cool, in the 20s.

Thursday:

The northwest upper level flow pattern will remain favorable for multiple waves to dive across the region bringing periodic chances for (mainly light) wintry precipitation through the end of the week. This first of which arrives Thursday morning. While this feature appears rather moisture starved, given modest warm advection ahead of this feature still suspect that we may get a quick hit of snow showers/flurries as the wave moves overhead, potentially enhanced locally by seeder-feeder processes depending on coverage of the low-level stratus. While flurries appears to be the most likely outcome, localized dustings of snow can't be ruled out. Once the snow/flurries end, southerly winds will help advect warmer air into the area through the day on Thursday, with forecast high temperatures in the low to mid 30s north of I-57, with upper 20s south.

Thursday night - Friday morning:

A more focused mid-level shortwave dives across the area late Thursday night into Friday morning and is expected to bring a period of wintry precipitation to the area. Models are coming into a bit better agreement in the local area seeing at least some precipitation with this and have accordingly boosted precipitation chances into the 30-40% range (and will likely need to be increased further with later updates). However, there remain questions regarding the dominant precipitation type with this feature. A sampling of forecast vertical temperature profiles suggests there could be a period of snow, sleet, and/or freezing rain over parts of the area. Steepening mid-level lapse rates situated within the DGZ will be supportive of efficient snow production which could help cool the column even amidst modest warm advection, leading to snow being the dominant precipitation type. However, in the event of less efficient wet-bulb cooling and/or stronger warm advection, we could end up with a wintry mix of snow, sleet and/or freezing rain. Have introduced a slight chance (20%) for sleet with this update but have held off on including freezing rain for now given the lower confidence in what would be potentially more impactful, even with very light precipitation amounts (under 0.05"). This will be a period to monitor over the next couple of days as confidence in the details increases. Any remaining snow/precipitation will gradually shift southeast of the area through mid morning Friday.

Friday afternoon:

In the wake of the early morning wintry precip, winds will turn northwesterly during the day on Friday. While northwest winds are typically associated with cold air advection here locally, upstream temperatures will actually be warmer than what we will have been experiencing previously. This should allow temperatures to warm well into the mid-upper 30s, and potentially lower 40s in some spots bringing an end to the long stretch of sub-freezing temperatures for much of the area. This "warmth" will be fairly short-lived, however, with temperatures quickly falling late afternoon/early evening behind a cold front, also potentially paired with a period of gusty snow showers (20% chance) as low-level lapse rates steepen in the wake of the front. Overnight lows are then forecast to drop back into the low to mid teens.

This weekend through early next week:

The weekend will start off cooler, with highs in the mid 20s to lower 30s with another weak wave potentially diving through the region Saturday night which may result in a few snow showers (15% chance), though there remain a fair amount of variability in guidance this far out. Temperatures are then expected to gradually warm each day through much of the upcoming week as we undergo a pattern shift with upper level ridging building back toward the region. In fact, many areas could see temperatures well into the 40s by Tuesday. With extensive ice cover on area rivers this will be a period to monitor for any potential ice jam flooding developing as we head into an extended stretch of above freezing temperatures.

Petr

AVIATION /18Z TAFS THROUGH 00Z THURSDAY/

Issued at 1155 AM CST Tue Feb 3 2026

Aviation forecast concerns for 18Z TAFs:

- MVFR lake-induced stratocu for ORD/MDW/GYY develops this afternoon and persists into Wednesday.

- Period of lake-effect snow showers mainly for MDW/GYY tonight into Wednesday morning. IFR vis possible at times along with some minor accums.

A subtle trough pushing south across Lake Michigan at midday will shift winds at ORD/MDW/GYY to NNE/NE shortly. This will also spread lake-induced MVFR stratocu into these terminals early this afternoon. Forecast soundings indicate this stratocu layer is fairly shallow, and warmer than more favorable snow crystal generation temps. Thus while can't completely rule out a few non-impactful flurries, do not think they'll be significant enough for TAF inclusion this afternoon except perhaps at GYY.

High-res models continue to indicate deepening cloud depth and colder temps aloft and a more substantial snow shower potential later this evening into early Wednesday morning, with guidance primarily highlighting the MDW-GYY terminals. Periods of IFR vis and some light accums (1" or less) are possible for these locations. At this time, ORD looks to be just northwest of the better snow shower coverage, though current probabilities (20%) are below mentionable TAF criteria. Will have to monitor position of the band later tonight in case this needs to be included for ORD, which would likely be in the 07Z-13Z time range if it occurred.

Otherwise, winds are expected to turn back to NNW later this evening into Wednesday. Farther away from the lake, VFR conditions are expected to prevail at DPA and RFD.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.