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 Warning in effect for Lake (IN) and Porter (IN) counties late Friday into Saturday. A Winter Storm Watch remains in effect for central and southern Cook County 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.

UPDATE

Issued at 853 PM CST Thu Jan 29 2026

Forecast appears on track with no big changed planned this evening. Did move the end time of the winter storm watch for central and southern Cook County to midnight Friday night as lake effect band will likely shift east into Indiana sometime Friday evening. While it could shift back west into Illinois sometime Saturday morning, that would likely be handled with a separate headline.

Guidance has been trending a bit slower with the arrival of the lake enhanced surface trough Friday morning. Slowed the timing of the snow arrival down just a bit Friday morning to trend in this direction, but it is still well within the advisory timing. Still looks likely that a band of potentially intense snow will accompany this trough as it moves inland, with a quick 1-3" of snow possible in the advisory area, especially the northern suburbs.

Decided to upgrade Lake and Porter Counties in Indiana to a winter storm warning, as the probabilities of totals over 6 inches near the lake are very high. Given the likelihood of mesoscale oscillations in the position of the band, which are nearly impossible to predict with much lead time, it will be hard to pin down precisely where the highest snowfall totals will end up. Should the band end up stationary in one area for extended period, then isolated totals over a foot would certainly be possible.

One note caution, for those looking at the somewhat modest QPF being offered in some of the high resolution models, keep in mind that snow to liquid ratios will likely end up in the 30:1 range or higher! Given the exceptionally favorable lake effect snow parameters, seems likely that this band will likely produce snowfall rates of 2"+ per hour at times Friday night into Saturday morning.

- Izzi

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 /06Z TAFS THROUGH 12Z SATURDAY/

Issued at 1110 PM CST Thu Jan 29 2026

Forecast concerns for the terminals...

- Burst of lake effect snow Friday morning resulting in a couple hour period of IFR to LIFR conditions at the Chicago terminals.

- Another round of lake effect snow is expected Friday afternoon through Saturday morning mainly in northwest IN. Where the lake effect band sets up will likely see significant snow amounts (in excess of 8 inches) and very low visibilities.

Generally quiet weather is expected overnight with FEW to SCT VFR clouds and light northwest winds around 5 kts. Heading into Friday morning, the band of lake effect snow currently off the shore of western MI will begin to pivot into northeast IL starting around mid-morning. As the band moves inland, a period (1-4 hours) of IFR to LIFR visibilities is expected as snowfall rates up to 1"/hr materialize at the Chicago area terminals. On top of the lake effect, a shortwave trough will also be pivoting through the area which may result in some scattered snow showers getting as far inland as RFD by midday Friday. Given the fairly short window of lake effect it appears accumulations with this first burst will generally be in the 1-4 inch range with lesser accumulation with westward extent.

While a brief break may develop at the terminals after the first round exits towards early afternoon, a more formidable lake effect band is expected to develop Friday afternoon and pivot into northwest IN by Friday evening. Given some uncertainty as to where exactly this band will set up have opted to maintain PROB30s at the Chicago area terminals for this band for now. That said, where the core of the lake effect band sets up in northwest IN expect snowfall rates to peak around 1-3"/hr which will result in very low visibilities (possibly less than a 1/4SM at times) especially at GYY. Depending on how long the band sits in one location, accumulations upwards of 6 inches are likely with some spots possibly getting amounts in excess of 8 inches.

The lake effect band is expected to persist through Saturday morning in northwest IN and may attempt to wobble back west towards IL towards the tail end of the TAF period. With uncertainty in how the band will evolve Saturday morning have opted to maintain a dry forecast for ORD and MDW after 00z Friday evening. However, cannot rule out a flurry or two late Friday night.

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

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

IN...Winter Storm Warning from 3 PM Friday to 6 PM CST Saturday 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.