textproduct: Chicago

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, focus shifts into primarily northwest Indiana Friday night-Saturday, though it could be close for parts of IL.

- Winter Storm Watches in effect for Lake (IN), Porter (IN), along with central and southern Cook late Friday into Saturday. Advisories in effect for Lake (IL), Cook, and Dupage Friday morning through Friday afternoon.

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

DISCUSSION

Issued at 314 PM CST Thu Jan 29 2026

A prolonged period of intense Lake Effect Snow (LES) continues to look increasingly likely (80%+ chance) for parts of the area Friday morning through early Saturday evening. This event will in two parts, an initial fairly fast-moving wave of intense snow showers late Friday morning through early/mid afternoon, and then a prolonged period of LES, likely beginning into parts of Cook county in NE IL late Friday afternoon/evening, before focusing primarily across our NW Indiana counties (and Lake/Porter) late Friday night into Saturday morning, before potentially sloshing west back towards the NE Illinois shore and coming to an end late Saturday.

Headlines...

The Winter Storm Watch remain in place across Lake and Porter counties in IN from late Friday afternoon through Saturday. The main changes to the headlines was to hoist a Winter Weather Advisory for Lake IL, Cook and Dupage counties from 9am Friday morning through 3 pm Friday afternoon to account for the first burst of snow expected to shift in off the lake. Thereafter, we have opted to add central and southern Cook county to the Winter Storm Watch, which will run from 3 PM Friday afternoon through 6 am Saturday morning, for the beginnings of the intense lake effect band.

Friday Morning through mid Afternoon Snow...

Lake effect snow will initially focus into an intense NNW-SSE oriented band over eastern portions of Lake Michigan later tonight as boundary layer convergence ramps-up along an approaching inverted surface trough shifting south and west out of western lower Michigan. Then, as we head into Friday morning, this intense band will be forced west-southwestward into northeastern IL (and possible parts of far NW IN) as a southward advancing synoptic scale trough shifts overhead. The primary timing for this heavy burst of snow will be in the 9 AM to noon timeframe, before spreading inland into the early to mid afternoon hours of Friday. There still remains some degree of uncertainty with how far inland the band of the more intense snow showers will reach. However, weakening boundary layer convergence along the inverted surface trough is likely to result in a weakening trend to the band of snow with inland extent Friday afternoon.

The band of snow the comes ashore in northeastern IL Friday morning is expected to be fairly progressive, but at least briefly intense. Impressive lake induced thermodynamics (lake induced ELs up to 10,000 ft) will support heavy convective elements within this band of snow, which is expected to support snow rates of 1-2" per hour, particularly in close proximately to the lake. While the residence time of this intense band of snow will only be up to 2-3 hours at a given location, snow rates this high could easily add up 2" to 3"+ and result in adverse travel conditions for a few hours on Friday. It is for this reason we opted to hoist a Winter Weather Advisory for areas within close proximately to the lake (Lake IL, Cook and Dupage) Friday morning and afternoon.

Late Friday afternoon through Saturday Lake Effect Snow...

This is the main period of lake effect snow we continue to be concerned with. While the latest guidance continues to focus the main show across NW Indiana late Friday night into Saturday, there are increasing concerns that the redeveloping intense lake effect snow band could impact portions of central and eastern Cook near the lake late Friday afternoon into the evening. The band may remain somewhat transient here, which could in turn limit the residence time of heavy snow rates. However, even a few hour period of snow rates of 2-3"+ could support isolated areas of 6"+ across parts of Chicago and the southern suburbs in southern Cook, we felt it worth while to include them in the Winter Storm Watch.

There continues to be a strong agreement amongst forecast guidance that strong northwesterly winds on the west side of the lake will act to drive the main focus for this intense lake effect band eastward into Lake and Porter counties in northwestern IN either late Friday evening or Friday night. Thereafter, the band of lake effect may oscillate back and forth a bit across parts of Lake and Porter counties as additional meso-lows shift southward down the lake and reorient the main band. It also remains plausible that some of the more intense snow showers could work back close to the Cook county shore for a period on Saturday. We will have to keep a close eye on this. Lake thermodynamics will be in the waning stages Saturday afternoon, so while embedded heavier rates will remain, overall breadth and intensity of LES is expected to be on a downward trend through Saturday afternoon before ending entirely into the evening.

While confidence is high in the occurrence of this intense and impactful lake effect band of snow Friday night into Saturday (1-2" per hour snow rates, which could easily support double digit totals), lingering uncertainties in the movement and exact placement of the band has kept us from transitioning any of the watch to a warning for the time being.

Sunday and Beyond...

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 /00Z TAFS THROUGH 06Z SATURDAY/

Issued at 552 PM CST Thu Jan 29 2026

- Wind shift from light NW to gusty northeast expected mid-late morning Friday

- Lake-enhanced convective snow showers are likely along and behind the front wind shift/cold front, highest coverage and intensity expected closer to the lake.

- Additional lake effect snow showers possible in the afternoon at ORD/MDW/GYY.

Challenging, lower confidence forecast Friday due to the typically challenging nature of lake effect snow showers. We're expecting pretty robust band of snow showers to accompany a cold front across the terminals mid-late morning Friday, hitting ORD/MDW first, then likely spreading inland to DPA, and possibly as far west of RFD, though confidence decreases as far west as RFD. There is still considerable spread in guidance in the timing of the wind shift to northeast and the corresponding onset of the snow showers. Opted to stick close to the timing of the previous TAFs, but worth noting that it could be an hour or so earlier or later than the timing in the 00z TAFs. By the 09z TAFs, there will hopefully be greater confidence on timing of the wind shift/snow onset timing.

Additional lake effect snow showers will remain possible through the afternoon Friday, with the highest chances at ORD, MDW, and GYY. Opted to stick with just a PROB30 for now as confidence is still low on if the Chicago terminals get hit with afternoon lake effect snow showers and if so, when it may happen.

- Izzi

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 from 9 AM to 3 PM CST Friday for ILZ006-ILZ013-ILZ103-ILZ104-ILZ105.

Winter Storm Watch from Friday afternoon through late Friday night for ILZ104-ILZ105.

IN...Winter Storm Watch from Friday afternoon through Saturday afternoon for INZ001-INZ002.

LM...Small Craft Advisory from 9 AM Friday to 6 PM CST Saturday for Winthrop Harbor IL to Gary IN.

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