textproduct: Chicago

KEY MESSAGES

- Widespread showers will continue across the area through 6-7 PM this evening. Isolated thunderstorms remain possible near and south of the Illinois and Kankakee River Valley's through early evening as well.

- 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.

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

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 some snow flakes may try to mix in at times. 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 /18Z TAFS THROUGH 00Z FRIDAY/

Issued at 1158 AM CST Wed Nov 11 2026

Key forecast messages:

- Period of rain this afternoon with MVFR conditions, primarily between 19 and 22z at the main Chicago area terminals.

- Northeast winds this afternoon turn north and becoming increasingly gusty overnight into Thursday.

- Lake effect shower (primarily rain) potential at the main Chicago terminals (more likely at GYY) Thursday afternoon and evening. A compact weather impulse and surface low moving into the area will result in a period of rain at the terminals this afternoon. The area of rain is currently moving into the Fox Valley as of this writing, and will move into the Chicago terminals by 19z. As it does, expect a period of MVFR VSBYs and CIGs, roughly between 19 and 22z this afternoon before the rain tapers from west to east into early evening.

Northeasterly winds will persist today. However, as the parent surface low shifts into the Ohio Valley tonight concurrently with a Canadian high building into the Upper Midwest, winds across our area will shift northerly and increase overnight into Thursday. Gusty northerly winds (gusts 25to 30 kt) are thus expected to onset at the terminals late tonight, likely after 08 or 09z, and persist into the day on Thursday.

Northerly winds and the influx of a colder airmass will also support the development of lake effect showers late tonight and on Thursday. The primarily corridor of these lake effect showers is expected to be into northwestern IN. However, the focus could briefly shift back westward into parts of far northeastern IL later in the day as a surface trough moves down the lake. Fortunately, surface temperatures look to remain just warm enough to keep precipitation types as rain through early Thursday evening.

KJB

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 4 AM CST Saturday for the IL and IN nearshore waters.