textproduct: Chicago

KEY MESSAGES

- Occasional chances for scattered rain showers will continue into next week. - Temperatures will gradually warm through Saturday before trending cooler early next week.

DISCUSSION

Issued at 111 PM CDT Thu May 7 2026

Expansive upper-level cyclonic flow remains entrenched across the Upper Mississippi River Valley, which is leading to a continuation of the generally cool and, at times, showery pattern. An upper-level shortwave propagating around the outer periphery of the cyclonic flow continues to pivot southeastward across the area this afternoon, which with steep lapse rates (500mb temperatures sampled near -28C on the 18Z DVN RAOB), is supporting widely scattered showers at press time. The highest coverage of showers through the afternoon and evening should generally favored near and south of I-80 (near a remnant boundary) and near the Wisconsin state line (near the core of the coldest mid-level temperatures). Southwest winds will remain gusty (30 to locally 40 mph) this afternoon, especially near showers where the deep layer of dry sub-cloud air will lead to efficient downward momentum transfer.

Tonight, coverage of showers should tend to favor areas south of Interstate 80 as additional subtle DCVA rides atop the aforementioned frontal boundary. A gradient in cloud cover will set the stage for a gradient in overnight lows, with values expected to fall toward the mid to upper 30s near the Wisconsin state line to the upper 40s near US-24. Patchy frost formation will be favored north of Interstate 88 and especially near the Wisconsin state line, though will withhold a Frost Advisory given the expectation for upper-level clouds to thicken toward daybreak (which may stall the downward dive in temperatures).

Tomorrow, another upper-level shortwave will pinwheel through the upper-level cyclonic flow and support the development of showers and perhaps a thunderstorm along the stalled frontal boundary. Forecast guidance continues to exhibit spread in the location of the boundary by tomorrow afternoon, though have noted a slight southward trend in the latest guidance. As a result, will paint low-end chance (20-40%) PoPs south of I-80 tomorrow, with the highest values near US-24. Elsewhere, partly cloudy skies and a modest push of low-level warm-air advection will help boost highs into the mid to upper 60s. Yet another upper-level shortwave will move across the region on Saturday, presenting another opportunity for a few showers. Temperatures on Saturday look to be the warmest of the past few days with highs in the upper 60s (north) to mid 70s (south).

Another reinforcing shot of seasonably cool air will follow the front Saturday night and result in a swift return to somewhat below average temperatures Sunday into the beginning of next week. With that said, ensemble guidance continues to advertise a strong signal for a notable warming trend by the May 16 to 17 timeframe, which is in line with climatology.

Borchardt / Izzi

AVIATION /18Z TAFS THROUGH 00Z SATURDAY/

Issued at 1222 PM CDT Thu May 7 2026

Southwesterly winds will become increasingly gusty through early this afternoon at the terminals, and the potential exists for a brief period of gusts near 30 kts through mid afternoon. Otherwise, an area of showers will generally track near/south of I-80, and have added a VCSH mention at GYY to account for this. At the Chicago-area terminals, the chances for precip directly impacting the terminals remains about 20-30 percent, too low to warrant a transition to VCSH and/or TEMPO groups.

One item we are closely monitoring is the potential for a lake breeze (possibly augmented by gusty outflow) to push southward towards primarily ORD later this afternoon and early evening. Chances remain too low to introduce a specific mention in the TAFs, but monitoring the 21-00z timeframe in particular for this with the boundary becoming apparent near the Lake County shoreline. If scattered convection develops near the WI state line, this may further increase the potential for a NE wind shift at ORD.

Otherwise, VFR will prevail tonight into Friday. Light and variable winds should trend light southwesterly through Friday morning. Lots of variability in the wind forecast for Friday afternoon, ranging from a lake breeze passage at the Chicago terminals to increasing SW breezes. Have continued to prevail light SW winds in the latest TAFs, but alterations may become necessary in future updates.

Carlaw

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 6 PM CDT this evening for Wilmette Harbor IL to Burns Harbor IN.