textproduct: Chicago

KEY MESSAGES

- Increasing signal for quick snow accumulations this evening with embedded robust wind-whipped snow showers/squalls leading to localized quick snow accumulations and rapidly-varying conditions. Hazardous travel conditions expected within heavier snow. - Up and then down temperatures are expected next week with occasional opportunities for (mainly light) precipitation.

DISCUSSION

Issued at 139 PM CST Sat Jan 10 2026

Through Sunday:

Main focus in the short term remains on the incoming stout shortwave and attendant vort max currently slicing across southern Iowa. Based on the latest guidance along with eyeballing recent IR/WV satellite trends, it looks like the main area of maximized DCVA will focus roughly south of a La Salle to Rensselaer line this evening. Guidance suggests a secondary maxima potentially focusing near the I-88 corridor. Both of these may lead to corridors of enhanced, wind- whipped snow showers to even bonafide squalls this evening.

Along and south of the southern corridor (La Salle - Rensselaer line):

More coherent/organized low-level f-gen will coincide with steepening low-level lapse rates and near-surface CAPE. The RAP has remained incredibly consistent since earlier this morning depicting a lobe of locally maximized ascent tracking within this corridor between about 5-6 PM and 9-10 PM (earlier west, later east) with peak UVVs pushing 30+ ubar/second through a deepening DGZ which is exceptionally intense. It's always difficult getting super detailed with these small-scale features even at this short of a time range, but based on the latest radar trends, feeling more confident that at least the northern terminus of this enhanced ascent will poke into our southern locales this evening.

Given all of this, along with the still stratiform nature to incoming precipitation, have boosted PoPs and snow amounts in this region this evening. Wherever this feature tracks, snow totals will likely overperform what's in the gridded forecast in a hyper-localized area (perhaps a 10-mile wide area or less), and it would not be surprising to see a few 3-4" amounts with the forcing profile supportive of very large dendrites. It's possible this axis ends up just south of our area, but it's too close to slice that thin at this point. The one slight detractor here is that air temperatures are currently in the upper 30s, and will only fall and then wetbulb to around freezing as this activity pushes through, but if rates become heavy, the large snowflake size would likely result in quick roadway accumulations. Will highlight this threat area with a Special Weather Statement, and if trends continue to deteriorate, a short-fused Winter Weather Advisory may be warranted (it's possible snowfall continues a bit longer than a snow squall warning is meant to handle and, while winds will become gusty, may not reach the level of a true snow squall).

Near the I-88 corridor:

Farther to the north, another area of locally enhanced DCVA is forecast to coincide with at least ephemeral low-level f-gen in the vicinity of the I-88 corridor. While modeled instability and lapse rates are higher compared to farther south, the remaining parameters are not as well tied together/coherent. That said, recent HRRR, HRDPS, and RAP runs have somewhat consistently shown a signal for localized streets of enhanced QPF in this area. Have also increased PoPs and snow amounts a bit. Main timing for this activity is also about 5 PM to 1 AM. Much like summertime convection, many locations will likely receive little or no snow with this activity, while nearby locales may pick up a quick inch or so.

Flurries and snow showers will likely persist after midnight tonight. A secondary vort lobe will push through the area towards midnight which will serve as another focus for more concentrated snow shower activity. The last push of light snow showers arrives towards daybreak, and activity should begin to diminish through the rest of Sunday morning. Lake effect snow showers will likely persist in the vicinity of Porter County towards midday with some localized higher accumulations there before activity winds down towards midday/early afternoon. Guidance suggests that a thin stratus layer may re-develop (or perhaps never fully erode) on Sunday and have increased sky cover a bit to cover this.

Carlaw

Sunday Night through Saturday:

Anomalously strong mid-upper ridging will establish near the Pacific Coast through next week, resulting in a predominantly northwesterly flow pattern across much of the northern CONUS. Seasonable conditions on Sunday evening will give way to a few days of solidly above normal temps (through Tuesday evening), followed by a return to more seasonable readings for mid-January through the rest of the week. There will be occasional opportunities for precipitation, though the deep northwest flow pattern will be unfavorable for any moisture-laden systems.

Following an evening dip in temps to below 30F Sunday evening, strong ~1035 mb surface high pressure will settle into the Mid- South. In response, as a fairly robust low-level jet shifts overhead, a commensurate increase in southwest winds will result in rising temperatures overnight into early Monday.

With the first in a series of clipper-type systems passing well to the north Monday into Tuesday, the breezy warm advection regime will result in highs in the lower to mid 40s Monday, near to a bit above freezing lows Monday night, and then highs into the mid-upper 40s to around 50F on Tuesday. Some spotty light rain showers or just sprinkles will be possible on Tuesday into the early evening as the next clipper wave reaches the area. The cold front trailing from an associated surface low pressure center passing through or just north of the northern Great Lakes will then shift across the area by the evening, bringing the early workweek stretch of mild temps to an end.

Mid-upper troughing will deepen over the eastern US on Wednesday as a few embedded short-wave impulses press southeastward. The cold advection regime on Wednesday should support at least scattered snow showers (30-50% PoPs still look reasonable for now), though marginal surface temps to start the day and the showery nature of the snow should tend to limit accumulation/impact potential. With the most robust mid-level height falls confined to the morning through midday, snow shower coverage and/or intensity may tend to diminish into the afternoon.

We'll then need to watch for a window of favorable lake effect thermodynamics Wednesday night into pre-dawn Thursday (if forecast mid-level subsidence is not too deleterious), supporting ~30-40% chance PoPs for portions of northeast IL and northwest IN. Any break following the possible lake effect snow showers will likely be short-lived, with signs pointing toward an additional clipper system or two affecting the region sometime in the Thursday PM-Saturday timeframe. Some guidance members suggest the clipper short-wave could temporarily become a cut-off low into the start of the weekend. If this comes to pass, warm advection driven snow late Thursday PM-Thursday night would be followed by on-and-off snow showers Friday into Saturday.

Castro/Ogorek

AVIATION /18Z TAFS THROUGH 00Z MONDAY/

Issued at 1155 AM CST Sat Jan 10 2026

Ongoing SN mixed with RA at the Chicago metro sites will end within the next hour or so. MVFR ceilings will also begin to scatter throughout the afternoon. Meanwhile, expect WNW winds to gust up to 25 knots through sunset.

A pair of compact mid-level waves, one over central Iowa and another over central Minnesota, will cross the northern half of Illinois in succession this evening as modest cold-air advection steepens low-level lapse rates. Isolated to scattered gusty SHSN are expected across the area throughout the evening. While the strongest SHSN will be widely isolated and may not affect every terminal this evening, they will contain wind gusts to around 30 knots and LIFR visibility. Have included TEMPO IFR visibility as most SHSN should remain in that range, but there is a distinct scenario where conditions vary between P6SM with FEW/SCT clouds and <1SM visibility multiple times during the evening.

The SHSN potential will diminish during the early overnight, but a final trough passing to the northeast late tonight may brush the Chicago terminals with SN for a brief 2-3 hour window. Otherwise, dry conditions are expected for the daytime hours on Sunday with NW winds gradually diminishing while backing W through the day.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 3 PM CST Sunday for Winthrop Harbor IL to Gary IN.

Small Craft Advisory until 3 AM CST Sunday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

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

Gale Warning from 3 AM to noon CST Sunday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.