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 /12Z TAFS THROUGH 18Z SUNDAY/

Issued at 539 AM CST Sat Feb 21 2026

Key Aviation Messages for the 12Z TAFs:

- MVFR ceilings expected to predominate through the period.

- A period of snow flurries/occasional snow showers is expected tonight into Sunday morning for the Chicago area terminals, though intensity/vis impacts are of low confidence.

- Northwest winds gradually increase later today/tonight with gusts around 25 kt by daybreak Sunday.

Early morning surface analysis places low pressure to the northeast of the terminals, over Lake Huron. Modest west to northwest surface winds were evident across the region, as well as a fairly extensive area of MVFR stratus. Significant breaks in the stratus have developed overnight along the western Lake Michigan shore from eastern WI into northeast IL/northwest IN, though northwest flow through the cloud-bearing layer suggests that with the exception of GYY, MVFR ceilings will prevail. Current cloud bases are in the 1700-2000 ft range beneath this deck, though there may be a gradual rise into this afternoon to around 3000 ft. Always tricky forecasting the edge of cool- season stratus decks, so confidence is medium at best in these trends.

A mid-level disturbance currently over the northern High Plains is forecast to track into the region tonight, carving out a deeper upper trough across the western Great Lakes region. This will result in cooling of the low-level moist layer and provide some weak ascent, which is expected to produce at least occasional flurries from this evening through Sunday morning for the Chicago terminals, along with a chance (30-40%) of intermittent snow showers at times especially over Lake Michigan and into northwest IN (GYY). While flurries appear to be a good bet, confidence in snow showers which may impact visibility and produce some minor accumulations is lower for ORD/MDW/DPA. Chances lower significantly farther west for RFD.

As the upper trough deepens tonight, strengthening of the surface low to our east will allow for a gradual increase in northwest winds, which will become gusty in the 20-25 kt range later tonight into Sunday morning.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 3 AM Sunday to 3 AM CST Tuesday for Winthrop Harbor IL to Gary IN.

Small Craft Advisory from midnight tonight to noon CST Sunday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

Gale Watch from Sunday afternoon through Monday afternoon for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.