textproduct: Chicago

KEY MESSAGES

- Waves of showers and storms are expected to continue into early next week. Many hours will be dry.

- Scattered to numerous storms are likely to occur in the area overnight into Saturday morning. The strongest storms tonight may be severe and produce torrential downpours.

- Near to slightly above average temperatures are expected this weekend before trending warmer next week.

UPDATE

Issued at 805 PM CDT Fri Jun 5 2026

Have made some adjustments to the near-term portion of the forecast through midnight tonight, primarily to lower pops significantly and raise temps a smidge.

Regional radar imagery indicates rain/showers which affected the area earlier today has shifted east into lower Michigan in association with a mid-level short wave and an embedded remnant MCV. Weak subsidence in the wake of those features has yielded relatively quiet weather conditions across the forecast area early this evening, outside of some spotty isolated light showers mainly north of the I-80 corridor within a region of weakly confluent low-level flow and modest but persistent warm/moist advection on southwest 925- 850 mb flow aloft. Some individual CAM runs have been fairly bullish with igniting convection across this area this evening, though WoFS runs and current satellite trends argue against significant development in the near term.

We do continue to monitor a couple of areas upstream of the cwa however for an expected increase in shower/thunderstorm coverage. The first is the westward extent of the aforementioned low-level confluent zone which can be seen as an area of slightly agitated cumulus clouds from northwest of the Quad Cities back through southeastern Nebraska (where thunderstorms have initiated since late this afternoon). The other to our north across central and northeast Wisconsin, where a linear convective line has developed and is propagating to the southeast. High-res guidance has been rather consistent in developing thunderstorms eastward in the vicinity of the confluent zone across southern Iowa near the Missouri border and eventually into norther/central Illinois overnight, while the Wisconsin storms continue to track southeast (likely in a weakening form but with an outflow boundary potentially maintaining enough forcing for convection to persist into parts of our cwa). Given otherwise warm, humid boundary layer conditions, some of these storms may pose a localized wind or hail threat after midnight tonight.

With the above scenario in mind, had lowered pops through the evening hours considerably (limited to slight chance or less than 25 percent), blending into our going higher chance/likely pops after midnight. Have also raised hourly temps and overnight mins a bit, with readings expected to be somewhat slow to cool off with our higher dew points and light southwest surface winds.

Ratzer

DISCUSSION

Issued at 409 PM CDT Fri Jun 5 2026

Through Sunday:

Extensive cloud cover this morning and afternoon prevented enough destabilization from occurring to support much of a thunderstorm threat from materializing today, even as a well- defined MCV passed close by. The bulk of the shower activity associated with the MCV will continue to peel away to the east over the next hour, leaving most of our area dry for the remainder of the afternoon and evening, though the soupy air mass will still likely support isolated showers lingering through much of this time frame. Still couldn't rule out some lightning occurring during this time frame as well, especially since equilibrium levels will rise and mid-level lapse rates will steepen going into this evening as a remnant EML plume is advected into the area from the west. That said, with forcing support diminishing with the departure of the MCV, confidence in lightning occurring through this evening is not particularly high.

Later tonight, increasing isentropic lift induced by a strengthening low-level jet will attempt to activate the EML plume, with ascent likely to be focused near and along a modified composite outflow boundary that will extend from near the I-80 corridor in our CWA back westward into southern Nebraska and northern Kansas. Aided by favorable jet dynamics aloft, convection is first expected to initiate along this boundary in the central Plains this evening before spreading eastward. Between eastward-surging cold pools driving this convection towards and potentially into our area after midnight and new cells popping near the surface boundary later on in the night farther to the east, at least scattered thunderstorms appear likely occur in our forecast area overnight.

CAM guidance continues to favor the greatest convective coverage near and south of I-80, which makes sense given the expected storm motions and initial positioning of the surface boundary, so have introduced likely PoPs for these areas. That said, in a true moisture-laden summertime air mass with plenty of instability aloft like this one, anywhere will ultimately be fair game for convection to occur, so have kept mid-range chance PoPs going outside of this more favored corridor for convection. In addition, another upper-level shortwave trough tracking through the Upper Midwest could yield a loosely- organized convective complex that tracks across Wisconsin tonight. Outflow associated with this complex may tend to propagate southward and could end up entering northern Illinois at some point late tonight or early tomorrow morning. If that does end up occurring, then this outflow boundary could serve as a focus for convection in our northern locales independent of what happens farther to the south.

The steeper mid-level lapse rates on the order of 7-7.5 C/km paired with the existing rich low-level moisture will yield around 2000-3000 J/kg of MUCAPE across much of our forecast area well into the night. Deep-layer shear values could vary considerably with location and time, depending on how far south the mid-level jet over the Upper Midwest dips and how quickly, so a messy mix of storm modes is possible. Regardless of the exact storm mode though, the aforementioned thermodynamic parameters should support some potential for locally strong to damaging winds and hail with the more robust convection. Precipitable water values between 1.25 and 1.75 inches will also result in torrential rainfall, and the somewhat parallel orientation of the low-level jet and isentropic forcing with respect to the aforementioned outflow boundary (or boundaries) does lend some concern for training convection and localized flash flooding. That said, the recent dry conditions may tend to limit this potential to our usual more flood-prone areas.

Any convection that lingers after daybreak on Saturday should diminish over the course of the morning as the low-level jet weakens with time. Away from any residual morning cloud cover and a lake breeze that will push inland, temperatures should warm solidly into the 80s. The upper 60s-low 70s dew points and associated instability will hang around for another day, leading to muggy conditions that could support additional thunderstorm development later on in the day. A relative lack of large-scale forcing mechanisms may tend to keep thunderstorm coverage somewhat limited tomorrow with most locations in our CWA favored to remain dry, but surface convergence along the lake breeze and any residual outflow boundaries from the overnight convection may still prove to be enough for diurnal thunderstorms to fire in a few areas. MLCAPE approaching 3000 J/kg amidst lackluster deep-layer shear could support the potential for isolated strong to damaging wet downbursts with the strongest storms tomorrow afternoon.

Ogorek

Sunday into Monday:

Toward the start of next week, the upper-level low currently traversing the US/Mexican border will finally begin lifting northeastward toward the Mississippi River Valley. The (by this point somewhat stagnant) humid airmass will hence be poised to support episodes of showers and storms as the upper-level low approaches and eventually moves overhead. Periods of cloud cover, as well as onshore flow forced by a surface high pressure system moving across eastern Canada, will lead to seasonable temperatures generally close to 80 degrees both days.

Tuesday Onward:

In the wake of the upper-level low, ensemble model guidance appears steadfast in depicting the development of persistent troughing across the Pacific Coast and upper-level ridging across the Midwest and Great Lakes region. As a result, temperatures should warm throughout next week with highs climbing into upper 80s to perhaps lower 90s by the weekend. When combined with the continued humidity, it'll start to feel more like summer next week. Will note that there are differences in the placement of the ridge next week, suggesting that there may be opportunities for storms (and associated localized natural air conditioning) in the general region as well.

(Note that the high temperatures in the mid to upper 90s and associated much higher heat indices being advertised by the NBM toward the end of next week are not currently supported by input ensemble data).

Borchardt

AVIATION /00Z TAFS THROUGH 06Z SUNDAY/

Issued at 634 PM CDT Fri Jun 5 2026

Forecast concerns include...

Chance of thunderstorms tonight. Wind shift/lake breeze Saturday afternoon.

Isolated showers will continue this evening and then there is a chance of thunderstorms late this evening through daybreak Saturday morning. Overall confidence remains low both for timing and for coverage. Current prob mention seems on track for now. If thunderstorms do develop, there could be a broken line that extends east to west across most of the local area. Any activity that develops is expected to drift southeast and weaken during the mid/late morning hours. Additional isolated showers or thunderstorms are possible Saturday afternoon into Saturday evening and while these may be close to the terminals, the most likely area for any development during this time period will be south of the terminals.

Southwest winds will gust as high as 20kt through sunset this evening, then turn more westerly through the night and possibly northwest by early Saturday afternoon. A lake breeze is expected to move inland Saturday afternoon, shifting winds east/northeast for the Chicago terminals. cms

LOT WATCHES/WARNINGS/ADVISORIES

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