textproduct: Chicago

KEY MESSAGES

- A prolonged period of lake effect rain showers (mixed with and possibly changing over to snow at times) is expected Thursday through early Saturday, primarily in northwest Indiana.

- There is growing concern for several inches of slushy snow accumulation Thursday night into Friday morning near the Illinois and Indiana border (southern Cook, eastern Will, western Lake IN) including during the Friday morning commute.

- Cooler temperatures are expected late this week into this weekend before another warmup occurs next week.

UPDATE

Issued at 900 PM CST Wed Nov 11 2026

The only change to the forecast this evening was to introduce 1 to 3" snow accumulations to the gridded forecast focused on the Thursday night through Friday morning timeframe centered along the Illinois/Indiana state line region (southern Cook, eastern Will, and western Lake IN counties).

Without getting too into the weeds, am growing concerned that precipitation type will change entirely to snow Thursday night within a quasi-stationary lake effect band parked along the IL/IN border opening the door for quick accumulations of snow. While the warm ground should tend to temper accumulations, cannot discount otherwise ideal conditions for efficient lake effect snow production. Did not want to get too carried away on accumulations at this point and will let the incoming midnight shift take a closer look.

Borchardt

DISCUSSION

Issued at 240 PM CST Wed Nov 11 2026

A shortwave trough and its associated surface low continue to spiral through northeast IL and northwest IN this afternoon. These features have lead to the development of widespread rain showers across much of the area and those showers are expected to persist through at least 6-7 PM this evening before shifting east into northern and eastern IN. Recent mesoanalysis also shows steep mid-level lapse rates (around 6-7 C/km) and some modest MUCAPE present across north- central IL (areas near and south of the Illinois and Kankakee River Valleys) which has generated a couple of isolated thunderstorms. While no severe weather is expected, taller storm cores have been producing some instances of pea sized hail and locally gusty winds up to 45 mph and that threat will likely continue through early evening as well.

Once the ongoing showers exit, a period of dry conditions is expected to develop and persist through the night for most locales. However, some lake enhanced rain showers are expected to redevelop after midnight along the western shore of Lake Michigan and gradually pivot into northern and northwest IN by daybreak Thursday morning. Given that lake effect parameters will still be somewhat marginal Thursday morning and the lack of a more dominant band, the lake enhanced showers will likely be somewhat transient and be wobbling across northwest IN and the IL nearshore waters through the morning. That said, another upper-level shortwave is forecast to dive across northern IL Thursday morning which could lead to some isolated light showers and/or sprinkles. Though, with the dry mid- level air expected to be in place away from the lake confidence remains low that any inland showers/sprinkles will actually materialize.

By Thursday afternoon, an inverted surface trough is forecast to pivot across Lake Michigan and northeast IL which should pull the ongoing lake effect/enhanced rain showers into northeast IL. As this occurs the lake induced instability will be increasing which should help the developing lake effect showers have some inland extent, but exactly how far inland continues to be somewhat uncertain. Regardless, the lake effect showers will continue to manifest into a dominant band by Thursday evening as the instability and convergence increases. Initially the dominant band will likely be near the IL-IN border as it organizes, but will gradually pivot into northwest IN and become quasi-stationary as it does so. Once the band settles into northwest IN Thursday night it is expected to remain over the area through Friday night. Initially, the more shallow lake induced inversion and warmer temperature profile will keep rain as the dominant precipitation type, but as temperatures cool Thursday night precipitation type may change to entirely snow. With surface temperatures expected to be in the mid-30s (33-36F) it looks like any snow accumulation would be very limited (less than a tenth of an inch) and mainly confined to colder and grassy surfaces. The potential for a rain/snow mix with the lake effect will persist off and on through Friday night but again with the marginal temperatures accumulations should be limited. Though, if snow does become the dominant precipitation type and persists as such for an extended period of time and/or snow rates approach an inch per hour, then some locally higher accumulations up to half an inch could materialize inland of Lake Michigan in northwest IN.

Outside of the lake effect, winds will also increase on Thursday as a strong surface high builds into northern Great Lakes. This will result in northwest gusts on Thursday around 30-35 mph with locally higher gusts in excess of 40 mph possible near Lake Michigan. While some breezy winds will persist through Friday gusts should be only around 20-25 mph.

The lake effect showers will taper from west to east in northwest IN late Friday night into Saturday morning leaving us with dry conditions through at least the middle of next week. Temperatures will remain seasonably cool through the weekend with highs in the 40s and nighttime lows in the 20s and 30s before rebounding towards more seasonable values (in the lower 50s) early next week.

Yack

AVIATION /00Z TAFS THROUGH 06Z FRIDAY/

Issued at 545 PM CST Wed Nov 11 2026

N winds around 10 knots early this evening will back NNW over the next hour or two while diminishing to under 10 knots. A cold front shifting across the area late this evening into the early overnight hours will then bring a band of sprinkles or periods of light rain with perhaps intermittent high-end MVFR ceilings. Behind the front, winds will settle NNW and gradually increase with gusts over 20 knots by sunrise.

A weaker secondary front will cross the area mid-morning Thursday, with a 20 percent chance for sprinkles and perhaps a few flurries. Winds will increase further behind this front, leading to NNW/N gusts over 25 knots through the afternoon.

Yet another trough tracking SSW across Lake Michigan mid to late afternoon will push an axis of lake effect rain showers into northeast Illinois. SHRA with IFR visibility are possible at MDW, with lower chances of sub-VFR visibility at ORD as the SHRA remain east of the terminal. Have maintained PROB30 IFR(MVFR) at MDW(ORD), though a transition to TEMPO may be required in future TAFs. The main axis of lake effect showers should shift east of the Chicago terminals by early evening and settle into northwest Indiana.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from midnight tonight to 6 AM CST Thursday for the IL nearshore waters.

Small Craft Advisory from 5 PM Thursday to 4 AM CST Saturday for the IL and IN nearshore waters.

Gale Warning from 6 AM to 5 PM CST Thursday for the IL nearshore waters.

Small Craft Advisory until 9 AM CST Thursday for the IN nearshore waters.

Gale Warning from 9 AM to 5 PM CST Thursday for the IN nearshore waters.