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 issued for Lake (IN) and Porter Counties. Advisories may be needed for parts of N/NE Illinois for Friday.

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

DISCUSSION

Issued at 314 AM CST Thu Jan 29 2026

Today and Tonight...

Largely quiet conditions will continue across the region today. In similar fashion to yesterday, wind chills will start the day in the 10 to 15 below range before steadily rising above 0 during the afternoon. A disturbance shifting across the Southern Plains will throw some additional high-level cloud cover across our southern locales, but any precipitation will remain focused well south of the region. Other than some light lake effect snow clipping parts of far NE Porter County this morning, no precipitation is expected today and tonight.

Friday through Saturday evening Lake Effect...

Periods of lake effect snow, intense at times, look increasingly likely for parts of the area Friday through Saturday evening. This somewhat prolonged event continues to look like it will come in essentially two parts, an initial fairly fast-moving wave of snow on Friday, and then a prolonged period of LES focusing primarily across our NW Indiana counties (and Lake/Porter in particular) late Friday afternoon and moreso Friday night through Saturday, before potentially sloshing west towards the NE Illinois shore and coming to an end Saturday evening.

Friday Morning and Afternoon Snow...

A slight slowing trend in the arrival of the initial batch of snow continues, with the bulk of activity now looking to occur after about 8-9 AM and into the afternoon. Have accordingly trimmed PoPs prior to 6 AM to just our nearshore waters, and slowed their arrival a bit more through our northern Illinois locales.

Boundary layer convergence is forecast to increase along the eastern side of the lake very late tonight and early Friday morning as an inverted surface trough begins to push south and west off of western lower Michigan. In combination with a southward-advancing synoptic scale trough overhead, expecting these features to drive a NNW-SSE oriented band of LES towards NE Illinois (and parts of NW Indiana) after daybreak Friday, and most likely in the 7 AM to 11 AM timeframe, before spreading inland through midday and early afternoon. Just how far inland this activity makes it remains an area of uncertainty, but the potential exists for a quick coating of snow as far south and west as about the I-39/I-80 corridors.

Thermodynamics will be supportive of deeper convective development, with progged equilibrium levels nearing 9 to possibly 10 kft as a roughly -20 C 850 mb airmass spreads southward down the lake. Some degree of shear within the lake boundary layer is advertised, however, which could to some degree limit LES organization. However, the presence of such coherent low-level convergence with an unstable boundary layer supports the idea of embedded heavy convective elements within the southwest-advancing plume of lake effect. Based on some of the recent CAM output, would not be surprised to see embedded mesolows, which can act to boost local snowfall rates.

The associated trough will be moving at a decent clip, which should limit the residence time of this initial batch of snow to 1 to maybe 2-3 hours at most. While this will cap the ceiling on amounts, am a bit concerned that snowfall rates (on a localized basis) could get pretty significant (1 to maybe 2"/hr), particularly in the first 15-20 miles of the lake where strong ascent through the DGZ and a very cold column will support SLRs near 25:1 (and even higher if ascent is more robust). As a result, this initial wave has the potential to be a quick-hitting but impactful one, with roads quickly becoming snow-coated to completely covered, with some potential for winds to gust around 35 mph or so (squall-like characteristics). Am most concerned roughly north and east of a Harvard to De Kalb to Joliet line and then east along I-80/I-94 and up to the lake where boundary layer lapse rates are forecast to become the steepest, allowing for inland development of more intense snowfall. Rates should tend to diminish south and west from there. It's conceivable that the BL flow is strong enough that some gaps in the snow shower activity develops, but that's not something we can depict with any confidence at this point. It's also possible that this activity punches even further inland than we have depicted in the gridded forecast at this time, particularly if an intense and cohesive band of snow manages to organize initially over the lake.

Through the afternoon, the main developing LES band to our north is forecast to shift south and east down the lake, possibly clipping the NE Illinois shoreline as it does with another potential burst of accumulating snow although this again looks like this will be another brief period of an hour or two.

For this period (Friday morning through the afternoon), given the brief-hitting nature and generally lower snowfall amounts (ranging from a coating to about 3 inches), current thinking is we should be able to handle this with a combination of Winter Weather Advisories and Special Weather Statements. Will defer this decision to the dayshift, but will ramp up our messaging for impacted travel on Friday.

Friday evening through Saturday Lake Effect Snow...

This will be the main period of lake effect. Latest guidance continues to focus the main show across NW Indiana, and in particular eastern Lake and Porter Counties. Initial activity early Friday evening may remain somewhat transient in nature, as strong northwesterly winds on the west side of the lake act to push LES eastward. With time, however, increasing NEly winds off of lower Michigan are forecast to focus BL convergence roughly in the N-S orientation down the lake Friday night into Saturday morning.

While lake induced ELs will start to fall a bit through Saturday morning, parameters will remain very conducive for periods of intense lake effect snow during this time frame, with a potential for rates intermittently in the 1-2"/hour range. The degree of band longevity in any one location still remains somewhat unclear at this time, with a good deal of west-east wobbling noted in recent guidance.

Uncertainty notwithstanding, given the potential for multiple hours of high snowfall rates which could easily get out of hand during this period, combined with an increasing signal for localized high accums in recent hires guidance, did elect to hoist a Winter Storm Watch for Lake (IN) and Porter Counties for this time frame where the potential for significant totals in excess of 6 inches is the highest. Elected to start the watch late Friday afternoon as opposed to Friday morning with the first wave. This was due to 1) limited accumulations in the first wave and 2) potential for a notable gap in activity before the main persistent LES develops Friday night. If quasistationary banding develops, double-digit totals would easily be in play with SLRs progged to be near 25-30:1.

We still can't totally rule out LES building as far west as Chicago Friday night/Saturday morning which would bring significantly higher totals into play. At this time, though, the guidance trend supports a more typical evolution involving snow bands organizing just to the east of the city, but this is something we'll need to keep a close eye on. Regardless, it does look like LES may back into Chicago later Saturday morning and afternoon, delivering one last burst of accumulating snow to parts of far NE Illinois before activity begins to wind down. Lake thermodynamics will be in the waning stages during this time, 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 through the evening.

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.

Carlaw

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/

Issued at 1100 PM CST Wed Jan 28 2026

No major forecast concerns are expected for this TAF period as an arctic high will be mostly in control. Therefore, expect mostly clear skies through Thursday evening before SCT to BKN VFR clouds move in late Thursday night. Winds through the period will remain northwest with speeds around 5-10 kts.

It should be noted that the potential for a period of lake effect snow continues to look likely on Friday. At the present time the lake effect is not expected to get into the terminals until mid-morning on Friday. So while no mention has been included yet, suspect future forecasts may have to entertain something for the lake effect.

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...None. IN...Winter Storm Watch from Friday afternoon through Saturday afternoon for INZ001-INZ002.

LM...None.