textproduct: Chicago

KEY MESSAGES

- Accumulating lake effect snow will result in travel impacts across parts of NW Indiana (Porter County in particular) through Monday.

- Tuesday will be windy and milder with southwesterly gusts to ~35 mph.

- Monitoring potential for accumulating snow somewhere in the region in the Wednesday night-Thursday timeframe. Too early to have much confidence in track of system and any local impacts just yet.

DISCUSSION

Issued at 256 PM CST Sun Feb 22 2026

Through Monday:

The main focus continues to be on lake effect snow trends into northwest Indiana. However, in the near term, we're also assessing the recent blossoming of enhanced snow showers over eastern Wisconsin to just off the Wisconsin shore. While the primary vort lobe is over northern Illinois as of this writing, a more subtle elongated 500 mb vort/impulse appears to be over north central WI, just west of the Green Bay to Sheboygan corridor. This appears to be contributing to the recent enhancement of snow showers, with possibly some upstream connection to moisture from Lake Superior as well.

Given the current south-southeasterly trajectory of the snow showers, it's unclear if these will make it into northeast Illinois. The associated mid-level impulse may start to weaken as well. Even if these snow showers make it down in some fashion into the Chicago metro, it doesn't *currently* look to be a repeat of Saturday evening over parts of Chicago. That said, we'll certainly keep a close eye on radar and observational trends and upstream webcams with respect to the potential for localized travel impacts.

Of greater note, the passage of the aforementioned mid-level impulse is forecast to veer winds to more northerly over Lake Michigan (340-350 deg flow vs. 310-320 deg as of this writing). Forecast soundings show a noticeable improvement of overlap of strong low-level lift with favorable lake induced thermodynamics. This could yield moderate to briefly heavy snowfall rates into parts of Porter County, and even as far west as the northeast half of Lake County (considering the decent returns already present there this afternoon). The big question mark is the behavior of the lake effect banding - ie. are there a couple of enhanced bands that evolve out of multi-cellular activity and then one band becomes more dominant and intense?

Recent runs of the HRRR and RAP in particular have been consistently farther west with a more intense band Monday morning, reaching the LaPorte/Porter line, or even just into Porter County. The HRRR and RAP do tend to have a westward bias with lake effect banding, so did not quite jump on this idea, but did bump up PoPs to categorical Monday morning for northeast half of Porter County (and likely into northeast Lake). Will advertise additional accumulations of 1 to as much as 4". Strengthening northerly winds tonight may also yield at least patchy blowing and drifting snow. If the signal increases for higher accums to reach into Lake County, we may need to consider issuing a Special Weather Statement this evening (or even perhaps expanding the advisory). Finally, if the heavier band does reach farther west Monday morning, we may need to extend the Porter County advisory, but confidence is low.

Outside of the lake effect potential, intermittent non- accumulating flurries across the entire area will gradually come to an end from west to east overnight into Monday morning with the dissipation of the persistent stratus deck. It will be a cold start to the workweek, with wind chills within a few to several degrees of zero either side during the commute owing to still blustery north-northwesterly winds. Highs will reach the upper 20s to locally around 32F Monday afternoon west of the lake induced cloud cover.

Castro

Monday Night through Sunday...

Northerly low-level winds will likely maintain shallow lake- induced stratocu across parts of northwest Indiana Monday evening and perhaps even some poor quality flurries. This stratus layer should erodeovernight however, as large-scale subsidence and drying in the wake of the deep east coast upper trough works to further lower inversion heights, decrease winds and erode the stratocu layer. An associated north-south oriented surface high pressure ridge will transit the forecast area overnight, allowing light winds to turn southerly by morning.

Meanwhile, guidance remains in good agreement in depicting a clipper system dropping east-southeast toward the upper Midwest toward daybreak Tuesday, with its surface tracking from northern Minnesota into the northern Lakes during the day while deepening to around 995 mb. While guidance continues to track the mid-level vort and strongest ascent north of the forecast area, the diffluent/divergent left exit region of a 150 kt upper level jet streak associated with the wave is progged to provide additional forcing to cool and saturate mid-levels, steepen lapse rates aloft and potentially produce some precipitation as far south as far north/northeast IL and far northern IN Tuesday.

NBM blend has maintained the trend of 20-30% pops north of the I-80 corridor, highest toward the IL/WI border. If any precipitation occurs, which isn't a lock, P-type would be snow during the morning/midday, with some rain or rain/snow mix later in the day as surface temps warm on strong south-southwest winds. The ensembles then trend dry in the evening and overnight. Speaking of those winds, as the surface low deepens to our north, gusts approaching 30-35 mph appear likely. Drier ECMWF/EPS guidance still indicates daytime RH values to the 25- 30% range in the afternoon. This would continue to present some potential for a heightened grass/brush fire threat across our south/southwest counties where precip is less likely and temps warm into the low-mid 40s.

12z global ensembles were in fair agreement with their depiction of an amplifying short wave tracking southeast from the Northern Plains into the Midwest during the Wednesday night through Thursday timeframe. EPS/GEFS/CMCE means remain loosely clustered with a surface low track near/south of our forecast area, and in the potential for accumulating snow across parts of the region. Confidence remains low in the fine details at this distance however, given differences in degree of phasing and amplitude of the wave. A fully phased stronger system could introduce p-type issues to parts of the area, while a weaker, farther south system would result in a sharp gradient on the northeast edge of the precip shield. Nonetheless, this period bares watching for the potential for some wintery impacts associated with this system. A brief warm-up to close out the workweek then looks to give way to another pronounced cool down as we close out February and start March (and meteorological spring!)

Ratzer/Castro

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1125 AM CST Sun Feb 22 2026

On-and-off flurries will remain possible through tonight. A secondary disturbance will move over the region later this afternoon which may result in another brief uptick in snowfall/lowering vsbys (have pushed back the PROB30 timeframe for this to account for the latest timeframe). Otherwise, gusty northwesterly winds will persist through Monday morning with generally high-MVFR cloud bases.

At GYY: periods of steadier snow will be possible tonight as lake effect snow organizes. The heaviest snowfall is expected to remain east of the terminal, but indications point to LES backing westward Monday morning. Given that we're already carrying two PROB30 groups for potential bursts of snow and generally low confidence in sub-MVFR conditions Monday morning, have held off on additional PROB groups at this time, but will need to keep an eye on the roughly 13-17z window for possible lower conditions.

Carlaw

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...Winter Weather Advisory until noon CST Monday for INZ002.

LM...Small Craft Advisory until 3 AM CST Tuesday for Winthrop Harbor IL to Gary IN.

Small Craft Advisory until 6 PM CST this evening for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

Gale Warning from 6 PM this evening to 3 PM CST Monday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.