textproduct: Chicago

KEY MESSAGES

- Very cold conditions will continue through Tuesday morning.

- A clipper system is expected to bring accumulating snow to parts of the area Tuesday night into Wednesday morning, especially for areas near and north of I-80.

- Two cold fronts, Wednesday night and Thursday night, may each bring a period of light snow or snow showers.

- Another period of bitterly cold temperatures expected Thursday night through this weekend.

DISCUSSION

Issued at 258 PM CST Mon Jan 19 2026

Through Tuesday:

Very cold conditions will continue into Tuesday morning, though it will be less uncomfortable feeling due to much lighter winds. A moisture starved mid-level short-wave will pivot across the area this evening and early overnight. For the most part, the main effect on sensible weather will be a period of mostly cloudy skies as the short-wave passes over the region. However, it's not at all uncommon to see a few flurries leaking out of the stratus deck in these setups. There have been a couple obs off to the northwest (southeast MN, far northeast IA, western WI) with hints of modest visibility reductions this afternoon and even a site or two with light snow (flurries) reported.

Had earlier introduced a mention of flurries in the gridded database this evening until a couple hours past midnight, and continued that this afternoon. These would be in the form of isolated streamers of very light (likely non-accumulating) flurries that may cause sporadic bouts of 3-6 mile visibility due to very small flake size (cloud bearing layer colder than DGZ). Clouds should then clear out by the pre-dawn hours as 1030 mb surface ridging extends to the local area from the 1035 mb high pressure center transiting the Mid South. Temperatures should be able to drop back to the 0 to locally -5F range for locations near/north of I-80 outside of Chicago by the diurnal minima just prior to sunrise, and into the low positive single digits elsewhere.

After a mostly sunny start to the day on Tuesday, mid and high level cloud cover will stream in from the west during the afternoon in advance of our next snow producing clipper-type system Tuesday night (details in next section). Afternoon highs will range from the upper teens near the Wisconsin border to the mid to locally upper 20s on Tuesday, coldest near the Wisconsin border and "mildest" in far southwest sections of the CWA.

Castro

Tuesday Night through Monday:

High latitude blocking across Alaska and Greenland will foster anomalous troughing across the central and eastern CONUS through the forecast period. This large scale pattern is consistent with the negative phase of the Arctic Oscillation, and is strongly correlated with below to much below normal temperatures and periodic snow chances from clipper type systems across our area. Accordingly, our primary concerns through the period focus on the threat for what looks to be another period of dangerously cold weather (particularly Friday into the weekend), along with the increasing threat for accumulating snow from two quick moving clipper systems (Tuesday night and Wednesday evening).

Global ensemble guidance continues to be in good agreement with the timing and track of the first clipper system shifting into the western Great Lakes Tuesday night. While the 12z HiRes guidance favors a farther north track of the accumulating snow Tuesday night (mainly over southern WI), we have opted to follow closer to the more consistent global guidance for the forecast Tuesday night into Wednesday at this time. Overall, this favors developing snow within a warm air advection zone across much of northern IL and far northwestern IN (along and north of I-80) mid to late Tuesday evening. Snow would then continuing during the overnight hours, before abating around (or shortly after) daybreak Wednesday morning. Accumulations do not look overly high with this clipper, but the potential exists for amounts of 2-3" north of I-88, with generally an inch or less southward towards the I-80 corridor (and little to no accumulation well south of I-80). Accordingly, expect untreated roads from I-80 northward to become snow covered and slick into the early Wednesday morning commute.

Following the end of the snow early Wednesday morning, temperatures may warm to near freezing during the afternoon in parts of the area just in advance of our next quickly approaching clipper system and cold front set to shift across the area Wednesday evening. Another rather quick (2 to 4 hour) "thump" of snow showers looks to accompany this front Wednesday evening. This may thus result in some additional minor accumulations, and a period of slick travel before tapering to flurries by midnight Wednesday night.

The main weather story later in the week continues to focus on the turn back into a period of dangerously cold weather (particularly Friday into Saturday) following a strong Arctic cold front and possible quick period of snow showers Thursday night. During this period, ensemble guidance favors the high latitude blocking to force a significant southward shift of a piece of the Polar Vortex into southern Canada and the Upper Great Lakes region. At the surface, this would be likely to drive a 1050+ mb Polar surface high and accompanying airmass southeastward across Saskatchewan and the Dakotas into the western Great Lakes Friday into Saturday. The magnitude of this Polar airmass could end up resulting in temperatures remaining below zero for afternoon high temperatures on Friday, with teens below zero temperatures at night.

We will also have to keep an eye on the evolution of what could be a major winter storm across much of the southern CONUS Friday into Saturday. At this time, it appears we may be locked deep enough in the Polar airmass to keep all of the wintry precipitation safely to our south, but we will continue to monitor this.

KJB

AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 528 PM CST Mon Jan 19 2026

Intermittent gusts to 20 kts will continue mainly at the Chicago-area terminals for a few more hours before diminishing this evening. Generally WSW winds around 6-10 kts are then expected through Tuesday afternoon. There remains a chance for some very light flurries later this evening, mainly during the 03-08z window but chances appear too low to continue a mention in the TAFs.

Winds early Tuesday evening may briefly turn SE, but would likely return to a S to SSW direction fairly quickly. Confidence is too low for a SE mention at this time.

Another disturbance will deliver the next period of accumulating snow to the region Tuesday evening and overnight. Have introduced an initial mention of -SN in the extended ORD/MDW TAFs at 04z, but refinements will be needed in future issuances. At this time, IFR vsbys appear like a good bet after 06z.

Carlaw

HYDROLOGY

Issued at 258 PM CST Mon Jan 19 2026

Area hydrographs and ice spotter reports confirm that ice continues to develop and spread across areal rivers. Localized ice jams are already present along the Rock, Des Plaines, and Fox Rivers. Continued cold temperatures tonight and Tuesday will cause ice to continue expanding and thickening.

After a brief warm-up in temperatures to above 20 degrees on Tuesday-Wednesday, another push of bitterly cold temperatures will arrive Thursday night. As a result, the threat for ice jams including localized flooding will increase further toward the end of the week and through the weekend.

- NWS Chicago

LOT WATCHES/WARNINGS/ADVISORIES

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

Heavy Freezing Spray Warning until 9 PM CST this evening for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

Small Craft Advisory until 10 AM CST Tuesday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.