textproduct: Chicago

KEY MESSAGES

- Another storm system will deliver a round of snow and rain, blustery winds, and falling temperatures Saturday through Sunday morning. Some wet/slushy snow accumulations are expected Saturday morning, predominantly north of I-80.

- Monitoring a threat for robust, wind-whipped snow showers Saturday evening which may lead to quick snow accumulations and sharply-reduced visibilities. - Up and then down temperatures next week with occasional opportunities for (mainly light) precipitation.

DISCUSSION

Issued at 215 PM CST Fri Jan 9 2026

Through Saturday Night:

Areas of low stratus will persist across the region this afternoon, and any clearing that occurs this evening will likely be fairly short-lived as warm advection increases in advance of our next weather-maker. This disturbance--a vigorous shortwave spinning across SW Kansas and the Oklahoma/Texas Panhandles--will eject northeastward across the central CONUS this evening and overnight. At the same time, interaction with a synoptic scale trough/upper low scooting across North Dakota and the Minnesota Arrowhead will take place which will eventually lead to cyclogenesis and a deepening surface low as these features pass overhead on Saturday.

In advance of all of this, moisture is forecast to increase this evening and overnight, which will manifest as a rapid expansion of low cloud cover and eventually drizzle/light showers. With some degree of ongoing clearing, temperatures may end up meandering down into the mid low/mid 30s this evening. However, with dewpoints currently in the mid and upper 30s and no notable advection of drier air, don't currently have significant concerns of prolonged sub-freezing temperatures causing initial icing issues with air temperatures largely expected to settle just above freezing.

Large scale forcing will increase rapidly very late tonight/early Saturday morning. This will drive a rapid expansion of precipitation, initially mainly north and west of I-55. As deeper saturation arrives, precipitation in this area should transition quickly to snow through about 5-7 AM. Forecast soundings indicate a brief window (2-3 hours or so) early Saturday morning with fairly robust ascent coinciding with the DGZ in addition to ephemeral pockets of near-upright instability. In addition to at least modest 850-700 mb fgen, this may facilitate a brief period of boosted precip rates through late Saturday morning. Surface air and wetbulb temperatures are generally expected to be at or just a hair above freezing during this period, which should largely limit snowfall accumulations to grassy and elevated, untreated surfaces, but envision there may be some SW-NE oriented transient banding with rates that may briefly get high enough to result in some slushy accums on some road surfaces across parts of interior northern Illinois. Based on the latest guidance, have slightly increased snowfall amounts along and north of I-88 and west of about I-355/94 (locally up to 2 inches), but again most of this likely won't accumulate on the heavily-traveled thoroughfares.

To the south and east of I-55, slightly warmer surface temps and a rapidly-arriving mid-level dryslot suggest any transition to snow won't amount to much before precipitation ends from SW to NE through midday and early afternoon. Isolated to scattered rain/snow showers will be possible through the afternoon, but other than briefly knocking down visibilities, no significant impacts are expected.

This may change a bit by early Saturday evening as a subtle surface trough axis pushes southeast out of Iowa and Wisconsin ahead of a robust 700-500 mb vort lobe. Air temperatures will be falling quickly into the 20s during this period, and forecast soundings indicate a quick increase in boundary layer lapse rates and moisture. Have increased PoPs a bit Saturday evening, with a mention of scattered snow showers across pretty much all of the forecast area. Not currently to the level of a significant snow squall set up, but quick coatings with wind- whipped snow showers appears to be on the table, mainly during the 6 PM Saturday to 1 AM Sunday timeframe. With some forecast guidance (extended RAP for example) developing upwards of 50-75 J/kg of near-surface CAPE (which might be a bit overdone), can't rule out the potential for some true squall-like action in spots, so something we'll keep a close eye on.

Snow showers may persist through the rest of the night, but the boundary layer is forecast to dry out with time. Intermittent lake effect snow showers may continue into early Sunday morning, mainly across parts of Porter County.

Carlaw

Sunday through Friday:

Anomalously strong mid-upper ridging will establish near the Pacific Coast through next week, resulting in a predominantly northwesterly flow pattern for the eastern 2/3 of North America. Seasonable conditions on Sunday will give way to a few days of solidly above normal temps (through Tuesday night), followed by a return to more seasonable readings for 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.

Sensible weather wise, blustery conditions through around midday Sunday (gusts to 30-35 mph) will result in wind chills in the single digits and teens. With little if any snow cover and increasing sunshine favored in the afternoon, highs should recover to near 30F to the lower 30s, near to even slightly above normal for the date (albeit with relatively chilly wind chills). The winds will diminish through the afternoon and into the evening as 1035 mb high pressure passes to our south and settles towards the Ohio Valley. Following an evening dip in temps (upper teens to mid 20s), the surface high will sink farther south, with a commensurate increase in west-southwest winds resulting in rising temps overnight.

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 upper 30s to lower 40s Monday, mostly above freezing lows Monday night, and then highs well into the 40s on Tuesday. Some rain showers are possible Tuesday afternoon and evening with the cold front trailing from low pressure passing through or just north of the northern Great Lakes.

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 (30-40% PoPs for now are reasonable), though marginal surface temps to start the day and showery nature of the snow should tend to limit accumulation/impact potential. We'll then need to watch for a window of favorable lake effect thermodynamics Wednesday night into Thursday morning, supporting (~30-40%) chance PoPs for portions of northeast IL and northwest IN. There should be a brief break in the wake of however potential lake effect snow shower activity plays out, with signs pointing toward an additional clipper system or two affecting the region sometime in the Friday-Saturday timeframe.

Castro

AVIATION /18Z TAFS THROUGH 00Z SUNDAY/

Issued at 1152 AM CST Fri Jan 9 2026

MVFR ceilings at TAF issuance should SCT over the next few hours in response to upstream drying and clearing. Sky cover may vary from SCT to BKN this evening into the early overnight, but favor SCT. NW winds currently gusting around 20 knots will continue to diminish to under 10 knots by sunset/23Z. Winds will also begin veering late this afternoon, shifting east of north around 00Z and SE by 06Z.

The entrance of an upper-level jet streak shifting northeast over the area late tonight through Saturday morning will provide modest forcing for precip generation during this period. Initially, existing MVFR clouds will thicken and begin to produce patchy drizzle prior to 12Z. As forcing maximizes after 12Z, higher precip rates will allow the DZ to transition to SNRA. Embedded within the SNRA will likely be locally higher rates of all SN with low-end IFR to possibly LIFR visibility in the 13-16Z window. At the same time, winds will quickly veer from SSE to W, with the shift to west of south occurring prior to any higher SN rates. Slushy accumulations up to around one inch are possible.

Precip is expected to end by around 18Z, with WNW winds increasing to gusts around 25 knots and MVFR ceilings persisting through the afternoon. An initial mid-level trough crossing northeast Illinois very late in the TAF period (22Z-00Z Sunday) could bring a period of SHSN. However, a more robust mid-level wave approaching from the northwest after 00Z (beyond the current TAF period) will provide much better support and higher chances of another band or two of gusty SHSN with IFR (or lower) visibility.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 1 PM Saturday to 3 PM CST Sunday for Winthrop Harbor IL to Gary IN.

Small Craft Advisory from 1 PM Saturday to midnight CST Sunday night for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.