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 half 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.

UPDATE

Issued at 904 PM CST Tue Feb 3 2026

Overall the forecast for a period of light lake effect snow showers and flurries tonight into Wednesday morning remains on track. Recent radar trends from TMKE continue to show some light echoes just offshore of Milwaukee, WI and these should attempt to organize into a band of lake effect snow showers/flurries over the next 2-3 hours. While surface convergence tonight will be quite strong, the lake effect parameters continue to look modest to say the least with ELs around 3000-3500 ft AGL and cloud top temperatures hovering in the -10 to -12C range as noted in the 00z sounding from Valparaiso University. Therefore, the expectation is for snow quality to be somewhat poor and not result in much accumulation (up to a couple tenths at best) though some reduced visibilities (3-5 miles) could still be seen directly under the band.

As for timing, the band should initially set up along the northeast IL shoreline between midnight and 2 AM and gradually wobble southward towards IN by daybreak Wednesday morning. The band should then continue its eastward progression across northwest IN through Wednesday afternoon but in a weakening state which should keep snow showers mainly confined within a few miles of the lake. Snow is expected to fully taper by 4 PM Wednesday as low-level moisture wanes.

For those not under the lake effect, expect mostly clear skies tonight to become partly cloudy on Wednesday. As a result, temperatures will dip into the lower teens tonight (upper teens to low 20s near the lake due to clouds) before rebounding into the mid to upper 20s areawide Wednesday afternoon.

Yack

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 /06Z TAFS THROUGH 12Z THURSDAY/

Issued at 1102 PM CST Tue Feb 3 2026

Forecast concerns for the terminals...

- Lake effect MVFR ceilings at the Chicago terminals and GYY through Wednesday afternoon.

- Light lake effect snow showers/flurries tonight mainly at GYY and maybe MDW.

Light radar echoes continue to be seen offshore of Milwaukee, WI which should begin to organize into a band of lake effect snow showers/flurries over the next couple of hours. Despite the strong surface convergence, lake effect parameters continue to look modest (as noted in 03z sounding out of Valparaiso University) which should keep the snow showers weaker and limit any accumulation to a couple tenths at worst. Furthermore, visibilities with the lake effect should generally remain VFR though a period of 3-5 mile visibilities cannot be ruled out especially at GYY. In terms of timing, expect light snow/flurries to start nearing MDW around 08z then GYY around 09z and persist through 13z to 14z respectively. Though, flurries may linger at GYY through Wednesday afternoon if low- level sufficient low- level moisture can persist.

Outside of the lake effect snow, MVFR ceilings will prevail at the Chicago terminals and GYY through Wednesday afternoon as clouds continue to ooze inland off of Lake Michigan. Elsewhere, VFR conditions will prevail through the forecast period. Winds will generally be out of the west-northwest through Wednesday afternoon with speeds around 5-10 kts but a period of northeast winds are expected at GYY overnight. Wind directions will gradually become more southwesterly Wednesday night.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

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