textproduct: Chicago

KEY MESSAGES

- Areas of freezing fog tonight in northwest IN will result in localized reduced visibility and slippery travel.

- A period of light snow accumulations are likely (60%+ chance) Sunday night into early Monday morning, followed by less cold conditions by midweek.

UPDATE

Issued at 911 PM CST Sat Jan 31 2026

A band of lake effect clouds continues to stream inland across far northeast IL and northwest IN at this hour. While the expectation is for these clouds to gradually scatter out overnight as a surface high moves overhead, when exactly this will occur remains rather uncertain. That said, some flurries are still be seen beneath these clouds and that will likely continue until the clouds scatter out. Though no accumulation is expected.

Outside of the clouds, an area of freezing fog has started to develop across portions of Porter County. Given the light winds and recent snow pack, it appears low-level moisture will remain sufficient overnight to keep fog around and possibly even allow it to spread westward with time. However, with the aforementioned lake effect clouds around it is unclear how far west the fog will make it. For now have introduced patchy freezing fog all the way to the I-57 corridor with areas of freezing fog for much of northwest IN. While there has been some localized dense fog (visibility <1/4 mile), the coverage has been rather isolated and thus have opted to hold off on a Dense Fog Advisory for now. That said, if the dense fog becomes more widespread then we may issue one later on tonight. Regardless, anyone in northwest IN and far eastern IL should be prepared for localized visibility reductions and slick spots where fog develops.

Otherwise, no big changes to the ongoing forecast. So expect another cold night with lows in the single digits and mostly clear skies (outside of the lake effect clouds). Winds will remain light and gradually become more southwesterly by Sunday morning. Heading into Sunday, any fog should erode shortly after sunrise with just gradually increasing clouds and temperatures warming into the mid to upper 20s by the afternoon.

Though, a shortwave trough will be diving out of Canada and towards the Great Lakes which does look to bring a period of snow Sunday evening into early Monday morning. Overall the snow looks to be more of a nuisance than anything else with reduced visibilities (as low as 1-2 miles) and some accumulations up to 0.5 inches. Since the going forecast has a good handle on the snow, no changes were made to this part of the forecast.

Yack

DISCUSSION

Issued at 149 PM CST Sat Jan 31 2026

Through Sunday Night:

We went ahead and ended the Winter Weather Advisory earlier as the lake effect behavior continues to show little organization. Also, the thermodyamics on the lake will not be getting any better, so we no longer see this being a big issue for the lake shore areas this afternoon. Nevertheless, except snow showers to continue this afternoon near the lake. They could even end up persisting into early this evening before ending altogether. Some occasional brief localized heavier bursts could also result in some minor accumulations, but amounts will generally remain under an inch.

Generally quiet (but continued chilly) weather is expected tonight as a surface ridge axis promotes light surface winds as it slides eastward over our area tonight. A clipper-like system will then pass north of our area Sunday as the surface ridge axis shifts to our east. As this occurs, the low-level flow will back southwesterly and promote warm air advection across the area Sunday into Sunday night. While this will help warm temperatures well into the 20s (to possibly near 30 in some areas), cloud cover will be on the increase through the afternoon. A period of warm air advection driven light snow is also likely (60%+ chance) to shift eastward across our area Sunday evening/night. Overall, this does not look to add up to much snow, with accumulations looking to generally be a half inch or less into early Monday morning.

KJB

Monday through Saturday:

Surface high pressure is expected to descend out of Canada and spread over the northern Plains Monday into Tuesday. An area of low pressure forming over northern Texas will attempt to move northeastward, but current ensemble guidance is allowing the strength of the high to suppress the northward advancement of the low and keep the better chances for snow in Central Illinois. That being said, the blend still provided some low end "slight" chance for snow around and just north of US-24, however, accumulations and impacts should be fairly minimal (if it actually snows at all).

Temperatures next week will remain below freezing next week, but considering how cold it has been recently, it should not feel as bad. High temperatures are expected in the twenties (and may even low 30s on Monday and/or Thursday). Overnight lows will drop back down into the single digits by mid week.

Northwest flow is expected to remain aloft, but there's not a good signal for any chances for snow through most of the work week. That should change, however, Thursday night into Friday morning. While there is still uncertainty in the details, models are showing fairly good consistency with the next clipper coming out of Canada which could provide the next chance for snow.

DK

AVIATION /06Z TAFS THROUGH 12Z MONDAY/

Issued at 1100 PM CST Sat Jan 31 2026

Forecast concerns for the terminals...

- Lingering lake effect MVFR ceilings through the early overnight hours.

- Areas of freezing fog in northwest IN outside of clouds.

- Period of snow Sunday evening through early Monday morning resulting in reduced visibilities and some accumulations.

The lake effect MVFR clouds that were eroding earlier have redeveloped across far northeast IL and portions of northwest IN near the IL-IN line. Guidance has unfortunately not been handling these clouds well and with recent satellite trends showing more lake effect clouds developing offshore there is a growing concern these clouds will have some staying power. That said, with a surface high moving towards the area have opted to lean somewhat optimistic in the TAFs and have the MVFR ceilings scattering out at ORD, MDW, and GYY between 08-09z. Though this timing is lower confidence.

Outside of the lake effect clouds, areas of freezing fog have developed across portions of northwest IN (namely Porter County). While there have been some instances of sub-mile visibilities, fluctuations in visibility continue to be seen owing to the somewhat patchy coverage and likely thin nature of the fog. Given the fresh snow pack in northwest IN and the light winds it seems this fog will persist through daybreak and continue to result in periods of IFR to LIFR visibilities at times. However, whether or not this fog will spread west into GYY and portions of eastern IL remain unclear due to aforementioned uncertainty with lake effect clouds. If the clouds do scatter out as forecast then GYY may see a period of patchy fog late tonight and thus have opted to maintain the TEMPO group for MVFR visibility here.

Otherwise, expect VFR conditions to prevail through Sunday afternoon. Winds tonight will remain light (speeds around 5 kts) with directions gradually becoming more southwesterly by daybreak. Heading into Sunday evening, a shortwave trough will be pivoting into the Great Lakes and bring with it a period of accumulating snow. Given the modest forcing it appears the snow will mainly be a visibility issue with a 3-4 hour period of IFR visibilities expected at the terminals. In terms of accumulation, the modest forcing and relatively progressive natures should keep totals in the dusting to 0.5 inch range for this event.

Snow is expected to end from west to east early Monday morning, but MVFR ceilings are forecast to prevail through the end of the TAF period. Winds will also become a bit breezier Sunday night into Monday with speeds in 10-12 kt range and occasional gusts around 20 kts possible.

Yack

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.