textproduct: Chicago

KEY MESSAGES

- Dangerously cold conditions are expected late tonight through early Saturday morning, with coldest conditions expected Friday morning.

- Fluffy accumulating snow paired with cold temperatures may cause hazardous to locally dangerous travel conditions late Saturday into Sunday.

UPDATE

Issued at 828 PM CST Thu Jan 22 2026

The forecast is on track this evening.

Recent radar imagery from KLOT shows the leading edge of the true arctic air now racing across northern Illinois at press time along the periphery of a building high pressure system in the northern Plains. Northwesterly winds will increase in magnitude right behind the front and facilitate aggressive cold air advection of bitterly cold temperatures from the Upper Mississippi River Valley into the Lower Great Lakes. The inherited forecast appears to be right on track with temperature trends thus far, and will result in low temperatures ranging from minus 15 near the Wisconsin state line to minus 5 near the US-24 corridor just after daybreak Friday. When combined with the wind, it'll feel closer to minus 35 near the Wisconsin border to minus 25 near US-24. The Extreme Cold Warning and Cold Weather Advisories set to go in effect overnight are hence in good shape.

(Note that the Extreme Cold Warning will convert to a Cold Weather Advisory at noon tomorrow as wind chills "warm" above minus 30. We try to confine warning-level products to the time frame when warning-level impacts will occur. It will still be uncomfortably cold all the way through Saturday morning, after which the Cold Weather Advisories across our entire area are currently set to expire).

Have also been monitoring snow showers organized in horizontal convective rolls along the Minnesota/Iowa/Wisconsin tri-border region, which will be poised to drop southward into our area overnight. The inherited forecast calling for flurries seems appropriate for this activity, though definitely can't rule out a streak or two of a dusting of snow where activity is most pronounced through daybreak.

The only thing change in our gridded database this evening was to lower dew points tomorrow and tomorrow night by 5 to 10 degrees to fall in the minus 30 to minus 40 range, in line with upstream observations across central Minnesota and recent HRRR/RAP guidance. Otherwise, felt everything else was in great shape.

Updated products will be sent soon.

Borchardt

DISCUSSION

Issued at 249 PM CST Thu Jan 22 2026

Through Friday night...

An arctic cold front will move across the area this evening ushering in a bitterly cold air mass in its wake. Strong cold air advection will continue through the night and into Friday, likely resulting in low temperatures occurring after sunrise Friday morning. The strong cold air advection will keep boundary layer well mixed, and when combined with the tight pressure gradient will result in strong and gusty northwest winds tonight into Friday morning. The strong winds combined with subzero air temps will result in dangerously cold wind chills. The coldest wind chills are expected Friday morning, ranging from 20 to 30 below over southeastern CWA to colder than 30 below at times northwestern CWA. No changes made to the Extreme Cold Warning and Cold Weather Advisory through Friday morning.

Not expecting much in the way of a temperature recovery during the daytime hours Friday as cold air advection continues through the afternoon. Did nudge high temps upward just a hair Friday, mainly across Chicago and areas south of I-88 where there is little or no snow cover. These areas will likely be able climb just barely above zero, with temps across far northern IL probably remaining slightly below zero. Winds will gradually diminish through the day, so wind chills should "warm" above -30 everywhere midday, but likely to remain in the 15 to 25 below zero range through Friday evening.

Increasing cloudiness Friday night will probably limit temps from completely crashing, though another night of subzero lows are expected. Diminishing winds may allow wind chills to creep above advisory criteria by late Friday night. Did opt to extend the cold weather advisory through 9 AM Saturday to err on the side of caution, since it would only take winds a few mph stronger to result in wind chills at or below advisory criteria.

Finally, satellite imagery shows an extensive field of horizontal convective rolls across MN, northern IA and WI. While these clouds are shallow, cloud temps are cold enough for ice nuclei to be present and it is common for arctic dust type flurries to fall from these clouds. Have maintained flurries in the grids through tonight, but wouldn't be surprising if the flurry chances need to be carried into the daytime hours Friday. Can't rule out some lake effect snow (LES) showers clipping far northeast Porter County, but with mean flow 310-330, expect the brunt of the LES to remain east of Porter County. Winds will veer more northerly Friday night, but also weaken considerably so while LES will shift westward, it may also tend to remain mostly over the lake as land breeze develops and possibly results in lake induced meso-low forming.

- Izzi

Saturday and Sunday...

Forecast attention this weekend focuses on the major winter storm expected to have significant impacts across a good chunk of the southern and eastern CONUS. Locally, our area is expected to remain along the northern periphery of this large and expansive storm system, which naturally adds question marks with regards to how far northwest impactful wintery precipitation will fall. This is especially the case considering that a sharp north- northwestern cutoff in precipitation could occur over, or near parts of northwestern IL. Nevertheless, forecast confidence continues to increase in accumulating snowfall falling across much of central into northeastern IL and northwestern IN, most notably during the Saturday night and on Sunday timeframe.

A robust baroclinic zone will settle south across the southern states Friday into the weekend along the southern periphery of the Arctic airmass settling into the area tonight. Friday into Saturday, upstream height falls resulting form the strengthening aggregate troughing across the Rockies will induce a strengthening lower-level southerly mass response from the Gulf northward across this baroclinic boundary. This will in turn foster the development of an expansive wintry precipitation shield from the central and southern Plains late Friday into Friday night eastward across much of the southern half of the country Saturday into Sunday.

While a majority of the heavy precipitation with this system is expected to fall south of our area, as mentioned, chances continue to increase that much of our local area will experience some accumulating snowfall late Saturday through Sunday. The snow may come in two separate waves, with the first potentially coming Saturday afternoon into the evening, and a second coming Saturday night and on Sunday. Interestingly, with the Arctic airmass remaining in place across our area, the thermodyamics profile in which this snow will be generated within will feature a very deep Dendritic Growth Zone (DGZ), likely in excess of 10,000 ft. This will in turn foster a higher than average liquid-to- snow ratio than is typical for our area, with 20-25+ to 1 ratios certainly in play. Accordingly, even a tenth to two tenths of an inch of QPF that falls could result in a few inches of dry fluffy accumulation.

While confidence does continue to increase in at least parts of our local area experiencing some accumulating snowfall Saturday afternoon into Sunday, uncertainty remains with the specifics. For example, as noted above, one of the main question marks that remains is how far northwest into our area accumulating snow will extend. This as the precipitation looks to fight with drier air trying to advect into the region from the Arctic high to our northwest. The other question resides around the extent of lake enhanced snowfall along the south-southwesterly periphery of Lake Michigan Saturday night into Sunday. Low-level thermodynamic conditions do look favorable for this, and there is concern that this could result in higher snow amounts along and near the lakeshore into Sunday. Stay tuned for forecast updates!

One final note: Surface temperatures are expected to be in the single digits to the teens during the snowfall. Temperatures this cold will support snow covered roads, as traditional salt treatments will be less effective then when temperatures are in the 20s. For this reason, regardless of how much snow falls in a given area, expect adverse travel impacts in and near the region late Saturday into Sunday.

KJB

Sunday night through Thursday...

Cooler than average weather conditions are expected to persist through next week.

Northerly low-level flow is expected to linger Sunday night into Monday morning, before gradually backing northwest ahead of a building surface high pressure ridge. This will likely maintain a threat of accumulating lake-effect snow showers into northwest IN during this period, and potentially across far northeast IL (at least Sunday evening) as GFS/GEM guidance depicts slightly more north-northeasterly flow for a time. Accumulation potential appears greater in northwest IN however, with a longer period of favorable fetch and inversion heights which are progged to gradually rise Monday night beneath the mid-level trough axis and cold pool (temps approaching -22C at 850 mb). High pressure developing surface and aloft during the day Monday should eventually limit/end lake-effect for northwest IN, as subsidence gradually lowers inversion heights and low- level flow backs westerly.

Otherwise, the main theme through the extended forecast period will continue to be colder than average weather conditions across the area through much of next week. There may be some brief "moderation" in temps to around 20 degrees or so Tuesday in advance of another mid-level short wave, though a renewed push of colder air behind this system looks to reinforce arctic air across the region by mid- week. Aside from Tuesday, blended NBM guidance indicates daytime temps in the single digits to lower teens and nighttime lows in the single digits either side of zero are, with coldest wind chills approaching -15F to -20F at times. While low-amplitude clipper systems can't be ruled out in this persistent northwest flow pattern, there is currently no signal in ensemble guidance for significant precipitation beyond the potential Sunday night/Monday morning lake-effect.

Ratzer

AVIATION /00Z TAFS THROUGH 06Z SATURDAY/

Issued at 551 PM CST Thu Jan 22 2026

W winds will continue to gust to around 25 knots early this evening amid FEW/SCT VFR clouds. A strong cold front will cross the Chicago terminals around 03Z, with WNW/NW winds gusting around 30 knots late this evening into the overnight hours. Shallow SCT to possibly BKN filaments of MVFR stratus with sporadic flurries are expected in the wake of the front and continue through much of the night.

VFR conditions with dissipating low-level stratus and thickening upper-level clouds are expected on Friday as WNW/NW winds slowly diminish.

Kluber

HYDROLOGY

Issued at 828 PM CST Thu Jan 23 2026

Area hydrographs and ice spotter reports confirm that ice continues to develop, thicken, and spread across areal rivers. Localized ice jams are already present along the Rock, Des Plaines, and Fox Rivers. Bitterly cold temperatures tonight through the weekend will cause ice to continue expanding and thickening, increasing the threat for ice jams and localized flooding. At least some moderation in temperatures by the middle of next week may cause ice to begin shifting, before another period of bitterly cold temperatures arrives by next weekend.

- NWS Chicago

LOT WATCHES/WARNINGS/ADVISORIES

IL...Extreme Cold Warning from 3 AM to noon CST Friday for ILZ003- ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013- ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ103-ILZ104-ILZ105- ILZ106-ILZ107-ILZ108.

Cold Weather Advisory from noon Friday to 9 AM CST Saturday for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011- ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ103- ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

Cold Weather Advisory from 3 AM Friday to 9 AM CST Saturday for ILZ033-ILZ039.

IN...Cold Weather Advisory from 3 AM CST /4 AM EST/ Friday to 9 AM CST /10 AM EST/ Saturday for INZ001-INZ002-INZ010-INZ011- INZ019.

LM...Gale Warning until 3 AM CST Friday for Winthrop Harbor IL to Gary IN.

Small Craft Advisory from 3 AM to 3 PM CST Friday for Winthrop Harbor IL to Gary IN.

Gale Warning until 9 AM CST Friday for Gary to Burns Harbor IN- Burns Harbor to Michigan City IN.

Heavy Freezing Spray Warning until 3 PM CST Friday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

Small Craft Advisory from 9 AM Friday to 3 AM CST Saturday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.