textproduct: Chicago

KEY MESSAGES

- Up and then down temperatures are expected this week with multiple opportunities for precipitation.

- The main concern from a winter weather perspective is Wednesday into Thursday, with wind-whipped snow showers during the day Wednesday possibly followed by accumulating lake effect snow Wednesday night into Thursday morning.

DISCUSSION

Issued at 132 PM CST Sun Jan 11 2026

Through Monday:

No significant weather is expected in the short term. The main question relates to sky cover trends the rest of the afternoon and evening. A lowering subsidence inversion continues to chew away at the top layer of cloud cover, with regional satellite and webcams indicating the stratus deck overhead is extremely thin. Have recently seen quite a few holes and clearing developing across parts of NE Illinois and E Wisconsin. However, with the mean cloud-bearing flow backing to the southwest, additional cloud cover closer to our west should slosh eastward through the rest of the afternoon. There's a nicely-defined back edge to cloud cover though, and tracking this out suggests things should begin to clear out quickly near I-39 early this evening and then prior to midnight across the rest of the area.

Overnight, a stout shortwave currently pushing through southern Manitoba will pass to our north. Other than spreading some additional high cloud cover and increasingly southwesterly breezes, no significant impacts are expected in our area. Temperatures on Monday should warm into the low to locally mid 40s.

Carlaw

Monday Night through Sunday:

As has been advertised, anomalously strong mid-upper ridging will establish near the Pacific Coast through next week, with downstream troughing carved out across much of eastern North America. This represents the positive phase of the Pacific North American (PNA) teleconnection pattern, typified by a predominantly northwesterly flow pattern into the Great Lakes region. A stretch of solidly above normal temps to start the workweek will peak on Tuesday, followed by a return to more seasonable readings for mid-January through the rest of the week (near to below normal temperatures). The deep northwest flow pattern will be unfavorable for any moisture-laden synoptic systems, so overall precip amounts for the week will tend to skew towards the lighter end of the spectrum. This certainly does not preclude any impactful winter weather, however, with a persistent signal for accumulating lake effect snow somewhere downwind of southern Lake Michigan Wednesday PM into Thursday.

Forecast low temperatures Monday night are near to slightly above the normal high temperatures for this time of year (in the lower to mid 30s). This will provide a mild starting point for highs in the upper 40s to around 50F on Tuesday. The next clipper-type wave tracking into the northern Great Lakes will induce breezy west-southwest winds gusting to 25-30 mph. Isolated to widely scattered showers or sprinkles will be possible (20-30% PoPs) from the mid-level overcast out ahead of the system cold front, which will sweep across the area by Tuesday evening.

Most of Tuesday night will be quiet and breezy with temperatures still above normal. This will abruptly change by Wednesday morning as a robust PV anomaly dives southward across the area in tandem with a secondary cold front passage packing much stronger cold air advection. As winds shift to north- northwesterly with gusts up to 30-40 mph, strong large scale forcing will result in quickly blossoming snow showers on Wednesday.

While there's still some uncertainty in the westward extent of sufficient moisture through the DGZ, run-to-run continuity across the suite of global ensemble systems remains good on the whole and supports the latest NBM initialization's 30-80% PoPs across our forecast area on Wednesday (highest PoPs in northeast Illinois and northwest Indiana and lowest PoPs towards northwest and central Illinois). Depending on how this setup evolves from a convergence perspective, very steep low-level lapse rates could yield embedded snow squalls. While surface temperatures and mild antecedent ground conditions to start the day may initially limit accumulation/impact potential, temperatures falling into the 20s in the afternoon could paint a different story heading into the evening commute.

The main change noted from previous model cycles is slower and stronger with the PV anomaly/very cold closed 500 mb low diving south across the region. This entails cyclonic flow lingering into Wednesday night, important to most effectively tap into good lake-induced thermodynamics (vs. a more subsident regime serving as a limiting factor). It's much too early to be confident in the details for this period. However, from a pattern recognition perspective, accumulating lake effect snow is appearing more likely downwind of southern Lake Michigan (and possibly well downwind at that) due to deep near-unidirectional northerly flow and the synoptic assist from the departing PV anomaly. Could see some hybrid aspects as seen with the November 9-10 lake effect snow event per some recent guidance member depictions. The forecast northerly boundary layer flow continues to warrant boosting PoPs Wednesday night into the 50-60% range near/east of I-57 in Illinois into northwest Indiana.

Any break following the probable lake effect snow showers may be short-lived, with signs pointing toward an additional clipper system or two affecting the region sometime in the Thursday night-Saturday timeframe. Some guidance members continue to suggest that the clipper short-wave could temporarily become a cut-off low into the start of the weekend, which greatly increases uncertainty in how it will evolve. Maintained broad- brushed chance PoPs peaking in the 30-50% range Thursday night- Friday night given approximately that much ensemble member support. Nonetheless, the spectrum of plausible outcomes here is quite large, from on-and-off light snow/snow showers to little or no snow. Expect generally below normal temperatures to close out the week and into next weekend.

Castro/Ogorek

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1130 AM CST Sun Jan 11 2026

Ongoing MVFR ceilings may SCT at times this afternoon as a lowering inversion results in shallower cloud depths, but this will be countered by diurnal enhancement of the clouds. A more robust stratus deck currently over eastern Iowa and western Illinois will then advect over the area amid backing SW flow early this evening. Have therefore continued MVFR ceilings into mid-evening until low-level drying erodes remaining MVFR clouds from west to east late in the evening. VFR conditions will then prevail through the remainder of the forecast period.

NW winds briefly gusting up to 20 knots early this afternoon will back SW through early evening. A low-level wind max this evening followed by a persistent stronger gradient flow overnight through Monday will continue to result in periods of gusts around 20 knots.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 3 PM CST this afternoon for Winthrop Harbor IL to Gary IN.

Small Craft Advisory until midnight CST tonight for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.