textproduct: Chicago

KEY MESSAGES

- A pair of clipper systems will race through the region through the end of the week. The first on Thursday will bring a chance for some light snow accumulations (less than a half inch) to parts of the region.

- The second clipper system late Thursday night into Friday morning has the potential to deliver a wintry mix to the area.

- A pattern change toward warmer temperatures (highs and lows both above freezing) may materialize by the middle of next week.

DISCUSSION

Issued at 219 PM CST Wed Feb 4 2026

Persistent low stratus along and east of I-55 has recently showed some signs of thinning and eroding along its western periphery, and this trend should continue through the afternoon. Farther to the east and near the lake, cloud cover appears likely to remain entrenched, potentially into and through the evening. Flurries/intermittent light snow showers will gradually focus mainly across northwest Indiana as the cloud-bearing flow turns north to northwesterly.

The first in a series of fast-moving clipper systems will move southward out of Wisconsin tomorrow morning. Large scale forcing looks appreciable as this feature rapidly shifts across the region, with 500 mb height falls on the order of 60-80 m/12 hours. While overnight guidance trended decidedly "wetter" with this system, that trend has not necessarily continued today, with a wide spread in forecast QPF across both the hires and medium-range guidance suite, all of which seems to be tied to the degree of low-level dry air in place. Even the incoming 18z HRRR appears to be trending a bit less bullish on precip intensity and coverage. All this said, forecast soundings even from guidance that does not formally produce precip looks very close to supporting light snow, particularly north and east of about a Rockford to Rensselaer line. Given the progged ascent with this feature, have continued to increase PoPs a bit Thursday morning through mid afternoon. P-types mainly look to be snow with this system, and the brief-hitting nature and general lack of deeper layers of instability are expected to cap snowfall accumulations to less than a half inch.

As the synoptic scale trough passes to our south and east, forecast soundings indicate a rapid loss of deeper saturation Thursday afternoon and into the evening. Lingering warm advection and associated modest forcing is forecast to remain in place, which leads the door open to at least a low chance for precip to end as a little freezing drizzle or very low-quality snow/drizzle ("snizzle") mix. At this time, modeled cloud ceilings look a bit too high, along with some signal that the 900-750 mb layer may tend to dry out with time that we have elected to forgo a mention of freezing drizzle. Will continue to keep a close eye on model trends, however.

Fast on the heels of this system, the next wave will pivot overhead late Thursday night through Friday morning. This wave looks a bit more compact than Thursday's clipper, but roughly similar in the magnitude of forcing, with significant DCVA forecast to shift across northeast Illinois and northwest Indiana through Friday morning. Additionally, guidance indicates this feature will also be accompanied by a plume of somewhat steeper lapse rates in the 850-700 mb layer, the result of which can be seen in QPF output from guidance like the ECMWF, with localized swaths of higher amounts over a tenth of an inch. Still noting a significant spread in the handling of the southwest terminus of the main precip shield with this system, however. NBM-delivered PoPs for late Thursday night through Friday morning did look too low given the latest ensemble guidance, so continued to paint mid range chance PoPs across the northeast half of the CWA, trending lower from there with southwest extent. P-types could end up being a bit more problematic with this system as intensifying W to WNW low-level flow is slated to drive an above-freezing airmass aloft into parts of the area early Friday morning which brings the potential for sleet and freezing rain into the picture.

It remains a bit unclear just how far northeast into the region any p-type change over to a wintry mix will occur, with some degree of dynamic cooling likely to persist across far NE Illinois, potentially maintaining all snow thermo profiles closer to the lake. Chances for non-snow p-types increase quickly the farther inland you go, and have continued a general wintry mess wording in the gridded forecast, but will note that significant uncertainties during this part of the forecast remain. If the convective nature of precip materializes with this system, could envision some road impacts and subsequent travel issues during the Friday morning commute, but uncertainly in the general evolution of things during this period remains quite high.

The above-freezing portion of the atmospheric column will cool through late Friday morning. While surface air temperatures may climb above freezing during the afternoon, wet bulb temperatures are expected to remain near to just below freezing through the day. As low-level lapse rates steepen in the deepening CAA push, some streaky snow shower activity may develop as the trailing 850-700 mb vort max rolls overhead. Additionally, have boosted winds a bit above the blended offering as boundary layer flow increases to around 30 kts.

Carlaw

A glancing blow of another pool of seasonably cold air will render temperatures to fall this weekend. Mean GEFS/EPS highs settle into the 20s on Saturday and warm toward 30 on Sunday. Will note the NBM, which informs our extended forecast, is currently 4 to 6 degrees warmer (if not even a bit more) than input ensemble suites. So, would expect our forecast highs to lower as we get closer and can more readily adjust the temperatures.

Next Week:

Ensemble model guidance remains in agreement that the upper- level flow will shift from a persistent northwesterly flow pattern to more of a southwesterly flow pattern through the course of next week. Am starting to see a fly in the ointment in a more pristine pattern shift, being a cut-off wave meandering along the US/Mexico border during the first half of the week. With that said, the signal remains in ensemble mean fields for temperatures to increase next week with highs generally in the 40s and lows generally near the freezing mark. There is still a signal for a synoptic system somewhere in the broad central US region in the February 11 to 14 timeframe, which would probably present the next opportunity for inclement weather.

Borchardt

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/

Issued at 1100 PM CST Wed Feb 4 2026

Key messages for the 06Z TAFs:

- Period of light snow/snow showers Thursday morning through midday. MVFR vis/cig conditions and accums from a dusting to half an inch possible.

- MVFR ceilings likely Thursday night.

- Another potential for wintry precip toward daybreak Friday, possibly as a SN/PL mix.

Weak surface high pressure ridge axis is drifting southeast across the region late Wednesday evening. Surface winds are turning light southwest behind the ridge, and will remain southwest through the day Thursday with some gusts in the 15-20 kt range possible in the afternoon. Winds will shift more west- southwesterly Thursday night, with the loss of gusts around or shortly after sunset.

A quick-moving upper level disturbance will approach the region from the northwest early Thursday morning, tracking across the area through early afternoon. Initial effects will be a thickening/lowering VFR mid/high level cloud deck overnight, with eventual development of at least intermittent light snow/snow showers expected after daybreak Thursday. Onset and duration times continue to be of medium-low confidence due to the initial abundance of dry air in the low-levels which will need to be overcome to allow snow to reach ground level. Various model guidance continues to show spread with timing and degree of deeper saturation, though highest probability for snow continues to favor development by mid-morning and persisting into early afternoon. MVFR cig/vis conditions (can't rule out brief IFR vis) are likely at times within the light snow, and accumulations from a dusting up to a half inch are possible. The loss of mid-level saturation in the ice-bearing layer suggests the potential for some patchy light FZDZ after snow ends in the afternoon, though the low-level cloud deck may ultimately be too shallow to support any additional precipitation. With low confidence in this occurring, have not included in TAFs.

Stratus may improve to VFR for a time Thursday afternoon, though there is considerable model support for MVFR cigs developing by Thursday evening and persisting overnight. Another quick-moving disturbance will approach the area predawn Friday, and with warmer thermal profiles may produce a wintry mix of SN/PL at onset. Have included a prob30 mention at the end of the ORD/MDW 30 hour TAFs to indicate this trend.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Gale Watch from Friday afternoon through Friday evening for the IN nearshore waters.