textproduct: Chicago

KEY MESSAGES

- Lingering wind-whipped snow showers and flurries ending this morning, followed by easing winds this afternoon.

- Up and then down temperatures are expected this week with occasional 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 251 AM CST Sun Jan 11 2026

Through Monday:

Scattered snow showers and flurries will gradually taper off across the area this morning, as a deep mid-level trough and vort max shift off to the east/southeast of the area. Can't rule out some light accumulations (less than half an inch) especially southeast of the I-55 corridor early this morning as the vort and mid-level cold pool pass overhead, though most areas will see little/no additional accumulation. The exception to this will be parts of north/northeast Porter county where around an inch of accumulation is possible during a period of lake-effect snow showers which will linger through mid-late morning. Otherwise, blustery and colder conditions can be expected, with decreasing cloud cover into this afternoon.

Early morning GOES water vapor imagery depicts the deep mid- level trough and embedded closed lower over the western Great Lakes region. An aforementioned strong vort/short wave was rounding the base of this trough over northern IL as of 08Z/2AM, with a cold pocket of -15C air analyzed at 850 mb. Beneath this cold pocket, RAP soundings indicate a deeply-mixed boundary layer with steep low-level lapse rates extending to nearly 800 mb. Resulting stratocu deck appears to be entirely within the DGZ (-12C to -18C), producing widespread snow showers and flurries across the area. While brief accumulations are likely with these, their scattered convective nature and relatively brief duration at any one location should limit amounts to less than a half inch in most areas. The vort and associated cold- pool will move off to the east-southeast early this morning however, allowing snow showers to taper to scattered non- accumulating flurries before ending. Over parts of northwest IN (particularly Porter county), north-northwest boundary layer flow will support lake-effect snow showers through late morning, before strong subsidence in the wake of the upper trough substantially lowers inversion heights. Dry air immediately above the inversion should help to limit lake-effect snow shower intensity somewhat even prior to that, though accumulations around an inch appear likely.

BLustery west-northwest winds gusting 25-30 mph this morning will gradually ease this afternoon, as weak surface high pressure ridging develops eastward across the Mississippi Valley. Associated subsidence should also help to decrease cloud cover from west to east as well. With some afternoon sun, temperatures should creep back to the lower 30s, though wind chills will remain in the low to mid 20s.

Surface winds will then turn southwest early this evening, in response to a quick-moving clipper dropping southeast across the upper Mississippi Valley and into the Great Lakes region. This will induce a 40-45 kt southwesterly low level jet overnight, which will make for breezy surface winds and even some sporadic gusts in the 20 mph range at times overnight. We'll probably see temps drop off into the mid-upper 20s during the evening, then remain fairly steady overnight with the winds and associated warm advection. These southwest winds will ease on Monday as the short wave tracks off to the northeast of the area, though continuing modest warm advection and partly cloudy sky cover looks to support daytime highs in the lower 40s for most areas.

Ratzer

Monday Night through Saturday:

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 be light. This certainly does not preclude any impactful winter weather, however, with a persistent signal for accumulating lake snow somewhere downwind of southern Lake Michigan Wednesday PM into Thursday.

Forecast low temperatures Monday night are near to above normal highs 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. Some spotty 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.

There's some uncertainty in the westward extent of sufficient moisture through the DGZ, though with good run to run continuity in most of the ensemble systems for this period, felt comfortable with PoPs increasing to 30-70%, highest in northeast Illinois and northwest Indiana. 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 in this period. However from a pattern recognition perspective, accumulating lake effect snow is appearing more likely downwind of southern Lake Michigan, 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 with the November 9-10 event per some recent guidance member depictions. With forecast northerly boundary layer flow, increased PoPs to 50-60% near/east of I-57 in Illinois into northwest Indiana.

Any break following the possible 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 suggest 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

AVIATION /12Z TAFS THROUGH 18Z MONDAY/

Issued at 556 AM CST Sun Jan 11 2026

Main Items of Note:

- Uncertain trends with sub 3kft CIGs into this evening

- Gusty winds, from west-northwest through early afternoon, and then from southwest/west-southwest this evening-Monday AM

There are no significant concerns this period. Scattered flurries are expected to end by about 15z. CIGs generally in the 2-3kft range have the potential to hang on a bit longer than indicated in the TAFs. Blustery northwest winds will ease and back to westerly later today. Forecast soundings suggest prevailing gusts should return later this evening and continue into Monday morning as winds further back to 230-240 deg. A fairly stout low-level jet will shift overhead tonight, though LLWS criteria appears unlikely to be met.

Castro

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.

Gale Warning until noon CST today for Gary to Burns Harbor IN- Burns Harbor to Michigan City IN.

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