textproduct: Chicago

KEY MESSAGES

- Rain expected to develop during the day Friday and continue into Friday night before ending Saturday. Widespread rainfall totals over an inch are possible.

DISCUSSION

Issued at 216 PM CDT Wed Jul 29 2026

Surface analysis early this afternoon exposes a center of high pressure over central Lake Michigan. This high is responsible for the dry weather and largely sunny skies today. It'll keep conditions quiet through tomorrow before ejecting to the east clearing the way for our next rain chances. Another seasonably warm day is expected tomorrow with highs forecast in the lower and middle 80s. Tomorrow will again be mostly sunny, but high level clouds will start moving over later in the day ahead of this next storm system.

A midlevel shortwave disturbance is churning some showers over the Intermountain West this afternoon. Over the next 36 hours or so, this wave will sharpen up considerably, evolving into closed mid level low by early Friday as it works into the Midwest. Widespread showers are expected to blossom around the deepening surface low over the northern Plains tomorrow and track southeastward into our general vicinity on Friday. There is fair agreement on the onset of rain in our west being late morning to early afternoon, and into Chicago during the afternoon hours. Widespread rain is then favored around the CWA Friday evening into early Saturday. There remains some uncertainty in trends through the rest of Saturday, but coverage should wane through the day generally from north to south. Most of the area looks to be dry by Saturday evening, maybe a bit earlier across much of Chicagoland. Where global guidance had previously had this closed low becoming cutoff and meandering about the lower Midwest early next week, now the favored signal is for the system to get sheared off to the northeast on Sunday. While a few lingering showers still appear possible on the backside of the low, mainly around the southern/southeastern CWA, precip potential for Sunday is on a downward trend.

Still not expecting much in the way of embedded thunder coverage with such cool low level air greatly limiting instability through the column. Some embedded storms will be possible, certainly, with some instability around and a strong forcing. There's some uncertainty regarding the track of the low and, while its still favored to track south of the CWA, a farther north track is still on the table. The NAM, UKMET, and RRFS are all farther north with the track and, perhaps more notably, the position of the effective warm front and northern extent of the more supportive instability. This is due to these camps resolving a deeper, more tightly wound upper low. If such a solution were to verify, this would boost embedded storm chances for areas that end up south of the warm front, though still not seeing a signal for anything too strong or severe in that case. There is concern, however, from a heavy rain perspective. Deep saturation with seasonably high PWATs just under 2" in conjunction with deep, dynamic forcing could result in periods of heavy, soaking rainfall. A widespread 1"+ of QPF through Saturday has been a consistent signal among deterministic camps and WPC has the area in a slight risk (2 of 4) for excessive rainfall.

Conditions will be slightly cooler this weekend with the storm nearby. Daily highs are forecast in the middle 70s to lower 80s, likely coolest all around on Saturday. Gusty northerly winds may develop on Sunday, especially down the lake, as a high encroaches from the north which may produce choppy waves and dangerous swimming conditions. A steady warmup is progged for next week with largely quiet conditions favored through the early part of the week.

Doom

AVIATION /18Z TAFS THROUGH 00Z FRIDAY/

Issued at 1218 PM CDT Wed Jul 29 2026

There are no key concerns to highlight for the 18Z TAF period.

NE winds around 10 kt will persist through the afternoon before going light and variable this evening into Thursday morning. SSW is favored in Chicago most of Thursday, but a lake breeze will attempt to protrude inland and turn direction to S or SE. Light winds are anticipated on either side of the lake breeze. Expect VFR throughout the period.

Doom

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.