textproduct: Chicago

KEY MESSAGES

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

- Tuesday will be windy and milder with southwesterly gusts of 35 to 40+ mph.

- Monitoring potential for accumulating snow somewhere in the region in the Wednesday night-Thursday timeframe. Confidence is currently low in impacts locally.

DISCUSSION

Issued at 333 AM CST Mon Feb 23 2026

Through Tuesday...

Main focus continues to be on accumulating lake-effect snow in northwest Indiana today. High-res HRRR/RAP guidance continues to indicate a westward drift of some of the heavier banding into Porter county (and passably as far west as the Lake/Porter border) toward mid-morning. Inversion heights rise to around 6500 ft range with lake-induced CAPE of 100-200 J/kg, and linger into early afternoon before delta-Ts and north-northwest winds begin to decrease. Given these trends (though the newly arriving 06Z 3km NAM is not as far west as previously), have extended the Winter Weather Advisory for Porter county through the afternoon as impacts are likely to persist. Additional amounts of 2-4" appear likely, with highest amounts still expected over northeast parts of the county. Will be issuing a Special Weather Statement for Lake and Jasper counties, to highlight some slippery travel potential where another 1-2" amounts are possible in east/northeast parts of those counties. Increasing subsidence later this afternoon and early evening is expected to lower inversion heights while drier low-level air arrives. This should allow for a fairly quick weakening/dissipation of snow showers to scattered flurries during the evening.

Elsewhere, guidance continues to struggle in handling the extent of lingering stratus across much of WI/IL beneath the western periphery of the deep upper level trough to our east. A couple of smaller- scale vort maxima continue to track south- southeast across the region this morning, with rising heights/subsidence developing in their wake midday into this afternoon. This, and low level dry advection (surface dew points in the single digits upstream) should eventually lead to large breaks developing in the stratus, though have gone a little more pessimistic with cloud cover at least for this morning. As this stratus deck continues to reside within the DGZ thermal range, scattered flurries will likely continue where cloud cover remains. Otherwise, it will remain cold and blustery with highs only in the upper 20s (near 30 southwest) today, with wind chills in the teens.

Winds will diminish fairly quickly later today into this evening however, as surface high pressure spreads east across the area. Attention then turns to the northwest, where a stout mid-level short wave is currently moving ashore over the Pacific Northwest. As models have indicated for the past several days, this disturbance is progged to zip quickly along the U.S./Canadian border tonight, then track east-southeast while amplifying across the upper Midwest and western Great Lakes region Tuesday morning. As previously noted, the primary forcing and swath of precipitation is expected to pass north of the forecast area. Increasing west-southwesterly flow aloft (and associated WAA/isentropic lift) and jet-level divergence does provide ascent across our area, mainly resulting in top-down saturation into the mid-levels. Substantial low-level dry air looks to be difficult to overcome however, with only some slight chance (<25%) pops along the IL/WI border for some spotty non- impactful light snow/rain.

Of greater impact locally, with be strong south-southwest surface winds which develop in response to the deepening sub-995 mb surface low tracking across the northern Lakes. Gusts of 35-40 mph, possibly to 45 mph appear likely per forecast soundings of some of the high- res guidance. In addition, there remains some spread in dew points Tuesday afternoon, though overall trend has be slightly downward as expected. Have bumped winds/gusts, and lowered dew points from NBM blended output. If some of the driest guidance verifies, RH values <25% would be likely which combined with the strong winds would support a heightened grass/brush fire threat especially in our south/southwest counties where temperatures in the mid-40s are likely.

Ratzer

Tuesday Night through Monday...

The focus in the long term forecast continues to be on a midweek synoptic system slated for Wednesday night and Thursday that's expected to impact portions of the Midwest. This is a tricky, quickly evolving synoptic setup that guidance is having a hard time getting a handle on, and there's still considerable uncertainty, even within individual ensemble systems, in everything from storm track to strength of the surface low to coverage and type of precipitation around the storm. However, most recent model runs are maybe hinting at a bit more of a consensus.

On Wednesday, a robust shortwave impulse will quickly eject out of the High Plains toward the southeast and drive a surface low across the region into Thursday. The past couple of days, medium range guidance has struggled with the track of the low and was suggesting for a time that the storm may attempt to track right overhead. While a handful of ensemble members suggest this is still a possibility, latest few iterations favor the idea of the wave getting shunted to the south with the help of an adjoining wave strengthening upstream and a phasing wave down in the southern Plains. The surface low is then progged to track across the lower Midwest/Tennessee Valley. The latest deterministic GFS, Euro, and Canadian, as well as their respective ensemble systems, have all picked up on this trend. Last evening's 00Z NAM looks into Thursday morning, and it's pessimistic on the influence of those two neighboring features. It allows the storm to track farther north across the CWA, similar to earlier global runs, but such a solution is becoming an outlier among available guidance.

A track across the lower Midwest could mean snow for some of our CWA. Most camps also resolve at least a narrow corridor of freezing rain in the transition between rain and snow as a low level warm nose looks to get wrapped into the storm. The GFS and NAM are most excited about the freezing rain potential. But another big area of uncertainty, as previously mentioned, is precip coverage around, and especially north of, the storm track. This boils down to discrepancies in the strength of the storm/amount of forcing and available moisture; ensemble forecast soundings exhibit a large spread in layer moisture. Still quite a lot needs to be resolved before getting into any finer details, but this will be one to watch for possible snow and ice impacts around the region. The NBM populated the forecast with blanket chance PoPs for snow around the area in the Wednesday night through Thursday morning window with a period of likely PoPs in our south, which seemed appropriate as it largely coincides with latest ensemble PoP guidance.

Considerable spread exists for the end of the week and this weekend. Following seasonably cool conditions on Wednesday and Thursday, guidance favors a bit of a warmup on Friday with highs possibly tapping into the 50s, but looking cooler and with much more uncertainty during the weekend. There is a signal for another synoptic system to move somewhere nearby early next week in the Sunday night to Monday timeframe. This one too offers some promise for a sizable footprint of wintry impacts in the region, but won't bother taking you down that avenue at this point in time.

Doom

AVIATION /12Z TAFS THROUGH 18Z TUESDAY/

Issued at 602 AM CST Mon Feb 23 2026

Key messages for the 12Z TAF period:

* At GYY, light to moderate lake effect snow showers into this afternoon with vsby reductions expected

* VFR snow showers and flurries at Chicago sites this morning

* MVFR cigs this morning with low confidence on return to VFR

* Strong southerly winds on Tuesday

Flurries and the occasional light VFR snow shower will fall on the Chicago terminals this morning, with additional flurries possible into the afternoon. Flurries may occur periodically this morning at DPA and RFD. At GYY, lake effect snow will ramp up through the early morning with waves of MVFR to IFR snow showers expected through the morning. Light snow showers and flurries may then linger through much of the afternoon.

Cigs have recently dropped into MVFR territory over all sites. Model guidance has a very poor handle on current conditions and timing on a return to VFR is of low confidence. It appears IL sites may be back to VFR by mid-morning but there is reason to believe MVFR could hang on into the afternoon. GYY will likely maintain MVFR at least through the morning if not into the afternoon.

NW winds will gust to near and over 20 kt this morning before subsiding during the afternoon and evening. Expect light and variable winds tonight going SSW during the predawn. Magnitude will build quickly through Tuesday morning with gusts over 30 kt expected by mid morning. The occasional gust to around 40 kt looks very attainable during the late morning and afternoon.

Doom

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...Winter Weather Advisory until 6 PM CST this evening for INZ002.

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

Gale Warning until 3 PM CST this afternoon for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.