textproduct: Chicago

KEY MESSAGES

- Bitterly cold conditions will persist through this morning. - Another period of very cold conditions will occur early Monday morning with wind chills or 15 to 25 below. - Fluffy accumulating snow paired with cold temperatures will lead to hazardous travel conditions in many locations from this evening through much of the day Sunday. The highest snowfall accumulations and greatest travel impacts are expected near and east of Interstate 55 and near/along the Illinois lakeshore.

DISCUSSION

Issued at 327 AM CST Sat Jan 24 2026

Through Sunday Night:

It's another frigid morning out there as the well-advertised Arctic air mass continues to make its presence known. Air temperatures at press time are below zero across the area with wind chills generally between -20 and -30F, coldest across our northern counties. These readings will not change much until after sunrise, and even then, a relatively thick cirrus canopy will hamper warming efforts to some degree, keeping today's high temperatures in the single digits to at or slightly above 10F. Did opt to extend the going Cold Weather Advisory until noon to better align that with the advisory expiration times of our neighboring WFOs, but the overall message of another frigid morning has not changed, so bundle up in multiple layers if you need to go outside!

Also ongoing this morning is a stubborn ribbon of lake effect snow in northwest Indiana. Will continue to message the likelihood of resultant slick travel conditions in northern Porter County (and possibly northern Lake County, IN later on) with Special Weather Statements. Eventually, the lake effect snow band will retreat offshore and back over Lake Michigan later this morning as near-surface flow on the band's eastern flank veers from an easterly to a southerly direction with time.

This weekend's weather headline-maker is the absolute unit of a winter storm that will produce significant wintry impacts across a large swath of the central and eastern CONUS, including portions of the Deep South. The storm's massive size can be attributed to the Arctic air mass clashing with a substantial poleward influx of Gulf and sub-tropical Pacific moisture. This has yielded an expansive swath of precipitation across the southern central CONUS this morning, which is only expected to grow in size today into Sunday as a strengthening sub-tropical jet continues to funnel moisture into the CONUS while a cut-off upper low off the coast of Baja California begins to eject northeastward while undergoing a complex phasing process with two northern stream troughs. Aided by broad upper-level divergence in the right entrance region of a westerly polar jet streak, this storm's precipitation will spread into our forecast area from southwest to northeast in the form of snow by as early as this afternoon. System snow will then likely continue across at least a portion of our forecast area all the way through late Sunday afternoon/evening. Lake enhancement will also likely start to occur Saturday night/Sunday morning, before transitioning to a more bona fide lake effect snow and lingering beyond the end time of the system snow until closer to midnight.

One lingering point of forecast uncertainty remains how far northwest the steadier snowfall will be able to spread with a strong Arctic high to our northwest supplying a feed of dry air into the area. While our northwestern counties could still see a period of light snowfall this evening, the steadier snowfall will remain focused in the southeastern half of our CWA (and within any lake effect snow bands) thereafter as the drier air attempts to gradually creep eastward. A sharp snowfall gradient will likely occur across our forecast area as a result -- one that will likely be tighter than what can reasonably be depicted in our gridded forecast database.

Wherever the steadier snowfall does end up occurring, an exceptionally deep dendritic growth zone and the aforementioned cold air temperatures will yield a dry, powdery type of snow with snow-to-liquid ratios favored to average out around or just above 20:1. With the more pronounced mesoscale forcing mechanisms remaining displaced to our south, snowfall rates aren't expected to be exceptional -- generally remaining at or below 0.5"/hour. Briefly higher rates closer to 1"/hour aren't out of the question, though, in the more robust lake effect banding and in our far southeastern counties during the height of the synoptic snowfall late Saturday night/Sunday morning as an increasingly coupled jet structure strengthens broad-scale ascent. However, even without eye-popping snowfall rates, the prolonged duration of the snowfall will still allow for anywhere from a few to several inches of snow accumulation to be observed wherever the steadier snowfall has some staying power.

Have hoisted a Winter Weather Advisory for roughly the southeastern half of our forecast area (plus Lake County, IL), where confidence is highest in multiple inches of snow accumulation occurring and hazardous travel conditions materializing as a consequence of the cold air temperatures making it easier for snow to accumulate on roadways. It is possible that some locations could end up seeing snowfall totals of 6" or greater, and did give consideration to a Winter Storm Warning for a portion of our southeastern CWA for that reason. However, with our presently forecasted snowfall amounts being borderline for a Winter Storm Warning issuance and most other headline decision factors (long snowfall duration, less-than- stellar snowfall rates, winds not expected to be particularly strong, etc.) pointing towards the issuance of an advisory over a warning, elected to go with an advisory headline. Did segment the advisory product accordingly to account for where snowfall totals may be higher relative to other areas. That said, if confidence increases in solidly 6+" snowfall totals being observed somewhere, then an upgrade to a Winter Storm Warning may eventually be warranted for those locations.

Ogorek

Monday through Friday:

Following the weekend system, an energetic and active upper pattern will remain in place with fast, northwesterly flow aloft likely to guide additional disturbances across the Upper Midwest and Great Lakes region through the week. Regarding late Sunday night/Monday morning: latest guidance suggest we may need some additional cold weather headlines during this period to start the week with wind chills in the 15 to 25 below range.

Latest indications point to generally precip-free conditions on Monday as fairly robust mid-level height rises spread in from the west through the afternoon. The nose of a ~130 kt jet streak will impinge on the region late in the day, but at this time only looks like it'll drag some increasing mid and high- level cloud cover overhead. Northwest to west-southwest breezes with a lingering fairly tight surface pressure gradient will hold wind chills largely below zero through the day.

On Monday night, a fast-moving and fairly robust disturbance is slated to press southward out of the Minnesota Arrowhead Region and across the Great Lakes. Latest guidance currently takes the bulk of the most intense large scale forcing with this system to our north, and will continue with a dry forecast in our area as a result. The associated surface low will eventually drag a reinforcing cold front through the area on Tuesday which will send air temperatures back down to around 0 degrees Tuesday night with colder wind chills. In the wake of the front, forecast soundings look a bit more supportive of some intermittent flurries as lobes of strong shear vorticity meander southward through the afternoon and evening with increased saturation in a thin layer at the base of a deep DGZ. Good agreement that the boundary layer flow will remain westerly enough to keep an follow-up LES to our east.

Another, potentially even more intense shortwave is forecast to drop more solidly across our area on Wednesday and Wednesday night. Guidance generally appears supportive of a period of light snow somewhere in the vicinity, although noting a fair amount of north- south spread in the current deterministic and ensemble output. At this point, didn't see any reason to stray from the NBM-delivered chance PoPs during this period. Where snow does fall, very cold temperatures in the single digits and teens will once again lead to travel impacts.

Beyond this time, forecast confidence breaks down a bit, but there's an interesting signal of a fast-moving vort lobe backing southwest across lower Michigan sometime during the late Wednesday night - Thursday timeframe. This could potentially restart the LES potential in our area, but confidence is pretty low in specifics at this time.

Carlaw

AVIATION /12Z TAFS THROUGH 18Z SUNDAY/

Issued at 548 AM CST Sat Jan 24 2026

Ongoing lake effect snow band just east of the GYY 10 mile ring will continue to shift west early this morning. Expectation is for the main axis of snow to begin pivoting northward a bit and may take the lowest vsbys north/northeast of the terminal, but given how close things are, elected to introduce a brief TEMPO in the 13-15z window for snow.

Elsewhere, VFR conditions are expected today with easing northwesterly winds eventually turning northeast to easterly this afternoon and evening. Light snow is expected to overspread the region late this afternoon, but more so this evening and overnight. No changes to the inherited PROB30 groups for IFR -SN at the front end, with the prevailing lines looking good timing wise to drop to IFR during the mid-late evening. At ORD/MDW, lake enhancement may support lower cigs/vsbys (possibly LIFR) towards Sunday morning, but not confident enough in this to justify TEMPO groups at this range. Uncertainty in wind trends also exists, mainly after about 10-12z Sunday when convergence associated with lake enhancement may result in winds turning NW at ORD and NNW to E at times at MDW.

RFD will sit at the northwestern edge of the main area of snow. As a result, uncertainty in snow timing and specific vsbys remains. Trend at this point is towards a period of IFR to low- MVFR vsbys in light snow overnight, but at this point elected to continue a PROB30 given lingering uncertainties.

Carlaw

HYDROLOGY

Issued at 230 PM CST Fri Jan 23 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...Cold Weather Advisory until noon CST today for ILZ003-ILZ004- ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019- ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104- ILZ105-ILZ106-ILZ107-ILZ108.

Winter Weather Advisory from 6 PM this evening to 6 PM CST Sunday for ILZ006-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023- ILZ032-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

Winter Weather Advisory from 6 PM this evening to 9 PM CST Sunday for ILZ033-ILZ039.

IN...Cold Weather Advisory until noon CST /1 PM EST/ today for INZ001-INZ002-INZ010-INZ011-INZ019.

Winter Weather Advisory from 6 PM CST /7 PM EST/ this evening to 9 PM CST /10 PM EST/ Sunday for INZ010-INZ011-INZ019.

Winter Weather Advisory from 6 PM this evening to midnight CST Sunday night for INZ001-INZ002.

LM...None.