textproduct: Chicago

KEY MESSAGES

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

- Central and southern Cook County were upgraded to a Winter Storm Warning (replacing previous advisory) and is in effect until midnight tonight for periods of heavy/intense lake effect snow through this evening. Hazardous travel conditions are expected closer to the lake in Illinois today as waves of lake effect snow continue. Light snow with occasional bursts of moderate snow farther inland in northern Illinois will cause localized hazardous travel.

- Significant snowfall accumulations and very hazardous travel are likely near the lake in northwest Indiana tonight into Saturday, with the potential for additional notable accumulations and travel impacts in Cook and eastern Will counties east of I-57 late tonight through Saturday morning.

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

UPDATE

Issued at 1006 AM CST Fri Jan 30 2026

As generally anticipated, the mid-level and surface trough axis configuration today is decidedly focusing lake effect snow banding near and on the west side of the lake. However, the intensity of the snow extending well north to offshore of Manitowoc, WI increases concern for bursts of moderate to heavy lake effect snow persisting into this evening for northeast Illinois. While this won't be a continuous firehose of snow like in a single dominant intense band, webcams under the heavier snow rates have consistently shown roads quickly becoming snow covered/hazardous.

With the previous advisory and watch configuration for central and southern Cook, there was some thought that there would be more defined breaks in the accumulating snow, which appears less likely at this point. Additionally on this note, comparing radar to recent HiRes simulations, the HRRR seems to have a better handle than the 12z NAMnest (which initialized too far east with the snow off the WI shore). This suggests the intense banding developing this evening has a better chance to impact eastern sections of Cook County (and possibly even Lake and northern Cook) before shifting into northwest Indiana tonight. Ultimately, we opted to just replace the previous advisory for central and southern Cook with a warning, in effect until midnight. Confidence isn't super high in exact trends yet, but felt that localized 6"+ amounts appear quite likely (especially near the lake), and more importantly the significant impacts to travel due to periods of 1-2"/hour snow rates and visibility as low as 1/4 mile.

We're keeping a close eye on webcams and road conditions in Lake and northern Cook as well (Waukegan Airport 1/4 mile visibility as of this writing) for a possible need to upgrade these counties from an advisory to a warning. As the snow band(s) come ashore today, convective snow showers may spread fairly far inland into areas where broad light snow is ongoing underneath the mid/upper trough. Should it appear this activity is more potent, we may need to consider advisories for this, or at least Special Weather Statement issuance. The Winter Storm Warnings for Lake and Porter County Indiana remain unchanged for now. DuPage County IL is also in an advisory given the closer proximity to the lake of northeastern sections of the county, though again, confidence is on the lower side regarding how things will play out farther inland in the Chicago suburbs.

Castro/KJB

DISCUSSION

Issued at 343 AM CST Fri Jan 30 2026

Through Saturday:

Several periods of primarily lake effect snow will result in locally higher snowfall rates and hazardous travel near Lake Michigan in northeast Illinois and northwest Indiana today through Saturday. There are three distinct periods of focus during this time:

1) Today: A surface trough will shift SSW across northern Illinois through the day as a mid-level convergent/LES axis drifts westward into northeast Illinois. Surface analysis indicates the existence a hybrid meso-low and small thermal/synoptic low over southern Lake Michigan early this morning. Some CAMs have picked up on this feature, which favor an enhanced east to west convergent axis on the northern edge of the low as it backs into northeast Illinois through the day. So while an initial LES push will bring a period of briefly poor travel conditions late this morning into the afternoon, a more focused lake-enhanced band of snow may settle near the IL/WI line for several hours late this morning into the mid-afternoon.

2) Tonight: Broader synoptic flow will back slightly with time as the mid-level trough moves south and east, allowing a developing dominant LES band or broken/braided band over western Lake Michigan to shift southward along the Illinois shore and into northwest Indiana this evening. Steepening low-level lapse rates with a reinforcing shot of colder air combined with inversion heights up to 8-9kft should result in intense snowfall rates of 1 to 2"+ per hour with this band. While residence time of the band at a given location in northeast Illinois will be under two hours, conditions will likely become very hazardous during this time. The band should wobble back and forth over northwest Indiana late evening into the overnight hours with continued intense snowfall rates. Very dangerous travel is possible over northern Lake and/or Porter counties tonight, with increasing N/NNW winds resulting in localized blowing and drifting snow.

3) Saturday: Synoptic flow will begin to veer N or even NNE (especially at 925 hPa and above) as inversion heights slowly lower under 6kft. There is a window during the morning when the dominant band should settle around the IL/IN state line when thermo profiles are still quite favorable. Rates of 1-2"/hr will be possible during this time, particularly with much of the LES convective layer in the DGZ.

When all is said and done, locations along Porter and Lake County IN will likely see totals in excess of 6", with some locations in excess of 12" not out of the question. Farther west, totals may exceed 6" over southeast portions of Chicago and into the south suburbs east of I-57.

Headlines: With the potential for LES to be more focused into far northeast Illinois into this afternoon, have extended the Winter Weather Advisory for all original counties to 00Z. Gave some thought to including McHenry and Kane with the expected convergent axis possibly residing well inland for several hours this afternoon, but confidence in higher impacts were too low at this time. The headline for Central/Southern Cook was a bit tricky, as advisory-level impacts are expected in all three windows noted above. However, there will be gaps between each window. Had to decide between an extended advisory, or maintain the watch and extend it into Saturday. With the potential for the intense LES backing into Chicago by daybreak Saturday, felt the watch was the path of least regret at this time. Otherwise, the Winter Storm Warning for Lake/Porter was left unchanged, while an advisory was added to eastern Will due to farther inland extent of the dominant band.

Kluber

Saturday Night through Thursday:

Active northwest flow will continue beyond this weekend's system and into next week, and will guide several disturbances across the general region through next week. Medium range guidance continues to resolve the first of these waves scooting across the Upper Midwest and Great Lakes region sometime during the Sunday PM - Monday timeframe. In general, large scale height falls don't appear all that impressive, with the main surface trough and associated low forecast to slide well to our north. However. fairly robust DCVA on the southern flanks of this feature, coupled with north-south transient bands of mid-level f-gen may be sufficient to crank out some light snowfall over parts of the area, particularly the closer to the Wisconsin state line you get. The fairly quick forward progression of this system, as well as a general lack of deeper moisture, suggests snowfall amounts will be light, probably limited to a few tenths to an an inch or so. Based on the latest guidance trends, it's possible dry air plays a role and ultimately limits snowfall chances with this feature as well.

Deterministic and ensemble guidance spread increases markedly after Tuesday, lowering overall forecast confidence during the middle and end of next week. With a lingering baroclinic zone just to our south, there's a potential for some continued precipitation chances even into Tuesday/Wednesday, but this is far from ubiquitous across the guidance suite.

While below normal temperatures are expected to continue into early next week, there' a decent model signal for at least a moderating trend during the middle and end of the week, with highs potentially pushing near and above freezing.

KJB/Carlaw

AVIATION /18Z TAFS THROUGH 00Z SUNDAY/

Issued at 1153 AM CST Fri Jan 30 2026

Forecast concerns include...

Periods of lake effect snow through Saturday. Easterly wind shift this afternoon, then northwest this evening.

A period of lake effect snow is moving west across northeast IL currently with additional lake effect snow across southeast WI and over central Lake Michigan expected to move south/southwest and across the Chicago terminals late this afternoon into early this evening. There may be a brief lull in the snow between these two periods of snow and attempted to show that improvement in the new forecast but trends will need to be monitored and its possible the timing for the lake effect snow later this afternoon may need to be adjusted. Though this next period of lake effect snow looks to be relatively short in duration, perhaps 2-4 hours at any location as it passes through. The lake effect snow is then expected to shift into northwest IN tonight with several hours of snow expected, possibly at GYY. The trend in the models is for the lake effect snow to swing back into far northeast IL mid/late Saturday morning. There is still uncertainty for how far west it may move and how intense it may be, but the potential warrants prob mention for ORD/MDW. Any of this lake effect snow may be locally heavy/intense, especially near Lake Michigan.

Prevailing winds are generally north/northwest or northerly ahead and in the current area of snow, but will shift easterly over the next few hours as the snow ends. Winds will then shift back northerly late this afternoon and then turn back north/ northwest this evening. Winds at GYY will likely favor more north/northeast tonight into Saturday. cms

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...Winter Weather Advisory until 6 PM CST this evening for ILZ006- ILZ013-ILZ103.

Winter Storm Warning until midnight CST tonight for ILZ104- ILZ105.

Winter Storm Watch from late tonight through Saturday morning for ILZ104-ILZ105.

Winter Weather Advisory from 6 PM this evening to noon CST Saturday for ILZ108.

IN...Winter Storm Warning from 3 PM this afternoon to 6 PM CST Saturday for INZ001-INZ002.

LM...Small Craft Advisory until 9 PM CST Saturday for Winthrop Harbor IL to Gary IN.

Small Craft Advisory from 6 PM this evening to 3 AM CST Sunday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.