textproduct: Chicago

KEY MESSAGES

- Chances for light snow across the region tonight into Sunday which could result in a dusting/light coating in spots.

- Thereafter, accumulating lake effect snow may result in travel impacts across parts of NW Indiana (Porter County in particular) through Monday.

DISCUSSION

Issued at 238 AM CST Sat Feb 21 2026

Through Monday:

Early this morning, a pesky low cloud deck is meandering over a majority of our CWA, while the rest of our area, namely our southwest and far northeast, sits beneath clear skies. Where the cloud cover resides, temperatures are found in the middle and upper 20s while they've dropped into the lower 20s where skies are clear. Similar sky conditions are expected during the day today with low clouds looking to remain over much of the CWA. This will likely have implications on temperatures today bringing slightly warmer conditions to areas that see more sunshine. Afternoon temperatures are largely expected in the lower and middle 30s. A fair NW breeze during the afternoon will hold wind chills in the 20s.

Early morning water vapor imagery depicts a low amplitude upper wave spinning off the lee of the Colorado Rockies and into the Plains. This system will advance into the Midwest later today into tonight. As the wave interacts with an existing low level circulation over Lake Huron, light snow is expected to blossom over the Great Lakes region tonight into tomorrow, which will likely include at least portions of our CWA. We could see snow showers begin as early as this evening and continue into Sunday. Being on the western flank of this system, highest coverage is anticipated into northwestern Indiana with some lake enhancement likely as well. A layer of dry near-surface air should help hinder impacts to an extent. However, a fairly deep, nearly saturated DGZ will overspread the area and enough attendant forcing should be swinging through to provide a decent chance for a period of snow showers and a coating of accumulation over northeast Illinois and northwest Indiana especially overnight, but chances are generally greater nearer to the lake. Guidance is in good agreement on a dusting to a few tenths of an inch tonight especially east of the I-39 corridor. Portions of northwest Indiana and especially Porter County could end up with close to an inch by tomorrow morning.

While snow chances will come to a close for most of us by sometime Sunday morning, the lake effect snow potential will gear up for Sunday into Monday mainly into northwest Indiana. Low level winds will orient NNW'erly on Sunday as a secondary vort is forecast to drop south over the lake with a cool airmass in its wake, setting the stage for an extended period of lake effect snow. Lake effect parameters are not off the charts but would certainly support periods of at least moderate snow: ELs of 7-8 kft extending into the DGZ and roughly 300-400 Joules of lake-induced CAPE. Periods of heavy snow will definitely be possible especially if a comprehensive band can develop, but tough to say at this point if that will occur. If such a band were to form, guidance looks to favor areas just east of the CWA for greatest impacts, but certainly can't make that call for sure. High pressure will approach from the west bringing an end to the lake effect chances by midday Monday. From this evening through then, parts of northwest Indiana, especially northern Porter County, could be looking at a few to several inches of accumulation. Tough to say the extent of impacts just yet, but hazardous travel is looking increasingly likely for areas east of I-65 for the back half of the weekend and possibly bleeding into the Monday commute.

NW winds will build this evening and continue to gradually increase through the night and into Sunday as a low level jet builds down with the system advancing in. Most of the day on Sunday should feature gusts around 25 to 30 mph. Breezy winds will continue into Monday before subsiding Monday afternoon.

Doom

Monday night through Friday:

Rising mid-level heights are progged to develop by Monday evening, in response to upper level ridging in the wake of the departing eastern North American long-wave trough. Forecast soundings indicate subsidence quickly lowering inversion heights over Lake Michigan, and dissipation of lake-effect cloud cover and any lingering flurries in northwest IN. At the surface, a north-south oriented high pressure ridge shifts east across the forecast area, allowing winds to become light and variable during the evening. Farther to the northwest, guidance is in general agreement in depicting a clipper-system tracking east- southeast across the Northern Plains, which induces southwesterly mid-level warm/moist advection flow, resulting in the development, thickening and gradual lowering of mid-level cloud cover across the area later in the night.

The aforementioned clipper is progged to transit the upper Midwest/Great Lakes region Tuesday, though there remains some guidance spread with respect to the exact track and amplitude of the wave. While the bulk of the available models maintain the primary axis of precipitation north of the forecast area, the more amplified ECMWF/EPS continue to clip our northeastern cwa with some measurable precip chances. Forecast soundings indicate substantial dry air at least initially below about 700 mb Tuesday morning, though ECMWF progs do exhibit gradual top- down saturation through the day. The dry low levels also support sub-freezing wet bulbs which would likely support some snow if precip does make it to the surface, and we'll have to continue to monitor track trends with later model runs. Latest NBM has chance pops mainly along/north of the I-90 corridor across northeast IL, and this appears reasonable at this time. Another item for continued monitoring is that the ECMWF/EPS also continue to indicate lower surface dew points than the rest of the guidance suite (and the NBM blend) with RH values below 30 percent across our southwestern cwa Tuesday afternoon along with breezy southwest winds and temps in the low-mid 40s. If this were to verify it could potentially result in an elevated grass fire risk in our southwest Tuesday afternoon.

Considerable guidance spread develops in the Wednesday through Thursday period next week, as models differ with phasing and magnitude of another short wave tracking southeast from the Pacific Northwest. The ECMWF/EPS indicates a more amplified wave a more northern track, with a deep (<990 mb) surface low passing north of the forecast area across WI Wednesday night. The GEFS/CMCE ensembles indicate a somewhat less robust and notably farther south wave developing a surface low toward the lower Mississippi Valley. Given the wide spread and low overall confidence in these solutions at this distance, have no reason to make changes to NBM blend which does indicate low (20-30%) pops during this period. Obviously temps trends and p-types may be significantly different between these solutions as well. There does appear to be better overall ensemble support toward the end of the period, however, indicating surface ridging Thursday night and then another amplified wave and surface low north/northwest of the area Friday with breezy southerly flow and milder conditions here.

Ratzer

AVIATION /06Z TAFS THROUGH 12Z SUNDAY/

Issued at 1044 PM CST Fri Feb 20 2026

Forecast concerns include...

Mvfr cigs overnight. Chance of snow Saturday night.

Mvfr cigs are slowly lifting across northeast IL with some clearing across east central WI and also across west central IL. There remains quite a bit of uncertainty for cig trends through daybreak and for now, have maintained mvfr cigs, which are expected to slowly lift to low vfr Saturday morning. However, this lifting may occur sooner along with some possibly scattering.

There remains a chance of light snow or snow showers Saturday night into early Sunday morning across northeast IL and then into northwest IN. The best timing may end up being in the early morning hours of Sunday and have shifted the prob later, but still quite a bit of uncertainty and changes can be expected with later forecasts.

Westerly winds around 10kt will continue into Saturday morning, with perhaps a few gusts at times. Winds will turn more northwest for Saturday afternoon into Saturday night with gusts into the 15-20kt range developing Saturday afternoon and possibly continuing into Saturday night. cms

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 4 AM CST early this morning for Burns Harbor to Michigan City IN.