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KEY MESSAGES

- Cold conditions will continue into the weekend with mainly subzero wind chills through Saturday morning.

- Threat for impactful lake effect snow continues to increase for Friday into/through Saturday. After likely accumulations and impacts in northeast/eastern IL on Friday, the focus may shift into primarily northwest Indiana Friday night-Saturday, though it could be close for parts of IL.

- There may be a period of light snow accumulations Sunday night into Monday, followed by less cold conditions by midweek.

DISCUSSION

Issued at 236 PM CST Wed Jan 28 2026

Tonight through Thursday:

It's a quiet, albeit chilly, Wednesday out there today. Temperatures early this afternoon sit in the teens but, with a 10-20 mph westerly breeze, wind chills around the area are in the single digits on either side of zero. A shortwave upper impulse is diving into the region from the northwest bringing a corridor of light snow and virga snow across central and southern IA and into western IL. Precip coverage, if it even lasts with so much dry air nearby, should stay out of reach to our south for the remainder of the day. Expect mostly sunny skies for the rest of today to give way to mostly clear skies tonight, allowing for another cold night ahead.

Increasing BL moisture over the southern end of the lake could result in a period of light lake-effect snow showers and flurries in parts of northwest Indiana late this evening into early Thursday. Coverage should favor areas east of our CWA and into southwest lower MI, but light snow will be possible as far west as the Porter/Lake county line. In the forecast, maintained some low PoPs mainly around northern and eastern Porter County where a dusting of accumulation is plausible. Any lingering snow or flurries will taper off to the east during the morning.

Lows overnight into early Thursday are forecast around to just below zero. Wind chills at the start of tomorrow are expected in the -10 to -15 range and staying below zero through the morning hours. High pressure building into the region during the day should allow for more mostly to partly sunny skies tomorrow, albeit with well below normal highs in low-mid teens (offset by much lighter winds than today/Wednesday).

Doom

Thursday Night through Saturday Night:

For the upcoming potentially impactful lake effect snow episode Friday-Saturday, while there are still several key items of lingering uncertainty, we're starting to gain a bit more clarity on bigger picture trends.

Here's a general timeline:

- Friday (6am-6pm CST): A snow band (potentially with embedded heavy rates) will likely come ashore sometime between 6 AM and noon into northeast Illinois. In addition to producing a burst of heavy lake effect snow near the lake, there may be a 1-2 hour period of accumulating snow farther inland (unclear exactly how far west and south) into northern IL and perhaps parts of central IL, with some snow into far northwest Indiana as well. The uncertainty regarding time of arrival of the, and exact locations and residence time of heavier snow rates lowers confidence in the specific details. With that said, the daytime hours of Friday are presently the highest confidence timeframe (50-60%) for accumulating snow and travel impacts into northeast IL/Chicago metro.

- Friday Night (6pm-6am CST Sat): An intense lake effect snow band will probably take shape and potentially focus into parts of northwest Indiana (particularly Lake IN and Porter Counties/60% chance and 40-50% chance into northern Newton-Jasper). Some guidance (mainly recent GFS/GEFS simulations) suggests parts of northeast and eastern IL could be affected as well (~40-50% chance in official forecast) near/east of I-57. Confidence is low-medium in the details for this period, though we have medium to high confidence that there will be an intense band somewhere south of Lake Michigan. This is the most concerning time window for a more prolonged period of heavy/intense snowfall rates.

- Saturday (6am-6pm CST): If the heavy/intense lake effect band materializes and indeed focuses into northwest Indiana, it may meander back west towards the IL shore or even into far eastern/northeastern IL. However, this is a significant "wildcard" aspect of the forecast. An overall majority of the more recent model and ensemble data depicts the lake effect focus being primarily northwest Indiana. Once again, the GFS/GEFS has consistently depicted the banding shifting or remaining farther west into IL. We certainly can't discount this scenario, though in our messaging we plan to emphasize a higher likelihood for far northwest Indiana (~60% into northern Lake IN). Our forecast confidence is low-medium in the details. There's also uncertainty in how long into the day the core of the lake effect snow maintains heavy snowfall rates.

- Saturday Night (6pm-6am CST Sunday): The intensity of the snow should decrease during this time. Only about 20-30% of the the global ensemble members hang onto organized lake effect snow for a part of the night, supporting 20-30% PoPs from the northeast IL shore to far northwest Indiana.

Due to the notable uncertainty still evident in the Friday- Saturday accumulating lake effect snow details, we deferred any winter weather headlines issuance to a later forecast issuance.

Meteorological Synopsis:

Late Thursday night, very cold air over the still relatively mild open waters of southern Lake Michigan (not expecting much deleterious effect from ice cover in the nearshore) will likely result in the development of a lake induced meso- low accompanied by heavy snowfall rates. This will be the result of very favorable thermodynamics augmented by large scale ascent from an incoming mid-level trough axis. There's overall solid agreement in this general scenario.

Into the day on Friday, as is very common in these setups, there's a large guidance spread in the evolution of the band out over the lake. From a somewhat bigger picture perspective, the sharp east to west mid-level trough axis traversing the region should result in the meso-low related banding moving southwest into IL. This could very well have at least 1-2 hours of heavy snow rates near the lake in IL (including Chicago) given inversion heights almost up to 10kft and strong ascent through the DGZ. With a time of arrival variance from as early as 6-7am to as late as 11am-1pm, this certainly lowers confidence in the details as alluded to in the general timeline. The band could take on a squall-like orientation westward into northern IL, though duration of accumulating snow inland would probably be only an hour or two.

After the passage of the mid-level trough axis late Friday into Friday night, inversion heights should come down some and thermodynamics may become slightly less favorable with time. Lake effect parameters should still remain quite favorable though for a well organized band and possible mesolow. The consensus low-level and boundary layer flow orientation (N to NNW) during this time conceptually favors northwest Indiana, though it's always tricky when meso-lows are present. It's close to impossible at this range to accurately predict how much or little the heaviest banding may stall over a given location. With last weekend's event in mind and it's 25-30:1 or higher snow ratios, snowfall rates could conceivably get out of hand Friday night into Saturday morning in the heart of the band.

Similar to warm-season convective forecasting, lake effect snow (also convection) is often affected by what happened prior. So exact locations are only a rough idea, but again, conceptually should favor far northwest Indiana. The GFS/GEFS has been most aggressively far west with the band positioning and also slower to degrade lake effect parameters. Wobbles in the orientation of lake induced convergence axis could bring the band(s) back near or onto the IL shore for a time on Saturday before the snow rates start to notably diminish. We're a bit skeptical of the GFS/GEFS insistence on keeping the band(s) organized all the way into Saturday evening, so our official PoPs are only in the 30-40% range Saturday afternoon and 20-30% range Saturday night.

Castro

Sunday through Wednesday:

On the heels of this weekend's lake-effect event, guidance is resolving a weakening synoptic wave pushing into the region from the northwest on Sunday. Quite a lot of uncertainty exists in the timing and structure of this system, but it looks like a decent shot at a period of light snow sometime in the Sunday PM through Monday timeframe. The more aggressive medium range camps paint a few to several tenths of accumulation around the area, but we'll have to see how expectations evolve behind this weekend's very dynamic synoptic setup off the east coast. This ongoing cold stretch, the coldest yet this season, is expected to gradually give way to more temperate conditions by early next week. However, near to below normal temperatures are favored through at least midweek with highs forecast to get up into the 20s and lower 30s.

Doom

AVIATION /18Z TAFS THROUGH 00Z FRIDAY/

Issued at 1113 AM CST Wed Jan 28 2026

No significant aviation weather concerns through the 18Z TAF period.

Surface high pressure ridge will build east-southeast across the upper Mississippi Valley and into western/downstate IL through the forecast period. West to northwest winds are expected, with occasional gusts around 20 kts this afternoon. A few thin, patchy clouds in the 2000-2500 ft range can't be ruled out into tonight, though VFR conditions are expected to prevail through Thursday.

Ratzer

HYDROLOGY

Issued at 230 PM CST Wed Jan 28 2026

River gauges, reports from local officials, and reports from trained ice spotters continue to indicate a few ice jams across the area due to the significant increase in river ice over recent days. With continued cold weather into next week, conditions will remain favorable for river ice formation. While no widespread flooding is expected, localized ice jams may occur.

- NWS Chicago

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.