textproduct: Chicago

KEY MESSAGES

- Showers and storms are expected today with the highest coverage southwest of a line from Rockford to Joliet to Rensselaer, and then areawide on Monday. - The strongest storms today and tomorrow will be capable of producing localized flash flooding and wind damage.

- Heat and humidity will build Tuesday, Wednesday, and possibly into Thursday with peak heat indices in the mid to upper 90s. - There is a low (20%) chance for thunderstorms Tuesday and Wednesday followed by a threat for severe weather on Thursday.

UPDATE

Issued at 1025 AM CDT Sun Jun 7 2026

Mostly sunny skies have been observed this morning along and northeast of a Dixon, IL to Fowler, IN line. With an upper level ridge axis analyzed just east of the forecast area, a weak shortwave embedded in the longer wave pattern to the west is expected to ride the westward side of the ridge today increasing cloud cover and provide better forcing for showers and thunderstorms with current radar showing a bit of an earlier show for storms west of the forecast area this morning. A stout northwest to southeast oriented instability gradient from just south of a Rockford, IL to Rensselaer, IN line should focus much of the activity this afternoon south and west of the Chicago Metro. Severe weather is not expected, but in this high CAPE/low shear environment, it would not be surprising if we had a few reports of funnel clouds today in the far southwestern portions of the forecast area. The primary hazards are mainly frequent lightning strikes, localized gusty winds, and efficient rainfall. Modeled RAP soundings show long skinny profiles with dew points in the upper 60s and p-wats approaching 2 inches. Localized downpours, or even torrential rain at times, is possible this afternoon. Soil moisture in areas along and north of Interstate 80 are still somewhat dry which lowers the concern for flash flooding for these locations. However, with recent rains there could be a higher chance for flooding for areas south of I-80.

DK

DISCUSSION

Issued at 248 AM CDT Sun Jun 7 2026

Early morning water vapor imagery depicts short-wavelength upper-level ridging across the Midwest between aggregate troughing over the Pacific Northwest and northeastern United States. A broad upper-level low is slowly lifting northeastward from the Southern Plains toward the middle Mississippi River Valley toward the center of the ridge. Closer to the ground, an elongated stationary front is present from the northern Plains through the Lower Great Lakes. The position of the front mirrors the shape of Lake Michigan across north central Illinois and northwestern Indiana thanks to onshore flow forced by a surface high pressure system centered over Lake Superior.

Over the next 24 hours, the aforementioned surface high pressure system will meander eastward into southern Ontario leading to a east-southeasterly wind direction across the Great Lakes. The stationary front will hence remain more or less in the same place today, stretching from near Rockford to Joliet to Rensselaer. Southwest of the front, continued muggy conditions (dew points in the lower 70s) will facilitate easy-to-achieve convective temperatures around 80 degrees altogether forcing a diurnal flare in afternoon showers and thunderstorms. Poor lapse rates (near 6 K/km) tied to tropical-like moisture (PWATs near 2 inches) amidst meager shear in the convective layer (around 25kt) will promote slow-moving spatially-small cells capable of torrential downpours and wet microbursts. More specifically, the strongest storms will be capable of producing rain rates will exceed of 2 inches per hour, localized flash flooding, and highly localized wind damage. Meanwhile, it is shaping up to be a fairly pleasant and dry day northeast of the front (including across much of the Chicago metropolitan area) with relatively lower humidity values and highs in the mid 80s (upper 60s to lower 70s lakeside).

Tonight, composite outflow from afternoon convection and a synoptic turn of the winds to adopt a more southerly component should allow for the frontal boundary to lift northeastward. As a result, muggy conditions are poised to spread across the remainder of the area by daybreak Monday. The core of the upper- level low will then pass overhead throughout the day, leading to another diurnal flare of slow-moving showers and thunderstorms. Like today, poor lapse rates, high column moisture values, and meager shear will promote torrential downpours and wet microbursts with the thunderstorms tomorrow. In other words, there will be renewed threat for localized flash flooding and wind damage. Should any slow-moving storm overlap with an urban area (Rockford or the Chicago metropolitan area), flash flooding could be locally significant (flooded roadways and viaducts). Finally, cannot rule out a few funnel clouds on Monday as the center of the upper-level low moves directly overhead. Highs on Monday will be in the upper 70s to lower 80s, which with dew points in the low to mid 70s will make it feel more like Florida than the Midwest. Showers and storms may continue even after sunset until the upper-level low finally pivots away from the area by daybreak Tuesday.

Tuesday through Thursday:

In the wake of the upper-level low, ensemble guidance depicts the reinforcement of upper-level ridging in the Midwest as troughing strengthens across the Pacific Northwest. The net result will be warming temperatures locally Tuesday and Wednesday with highs poised to return to the upper 80s to locally 90 (particularly on Wednesday). When combined with the (by this point) stagnant and humid airmass, heat index values will climb into the mid to upper 90s both days. It'll be the first taste of summer-like heat of the year.

At this point, our forecast favors Tuesday and Wednesday to be dry in our local area leading to little to relief from the heat. However, periodic upper-level shortwaves shedding from the aggregate troughing across the western United States may provide just enough ascent to break through strong capping at the base of an expansive EML plume across the Plains. While deep-layer shear will not be particularly strong into the Midwest Tuesday and Wednesday, the presence of an expansive reservoir of instability (nearly dry-adiabatic mid-level lapse rates atop seasonably most low-levels) and nightly low-level jets (terminating into the mid-Mississippi River Valley) does raise concern for any Plains convection to grow upscale into eastward- moving mesoscale convective systems (MCSs). In other words, any storms that develop upstream of our area would likely continue eastward into ocean of instability. With hints of such a threat depicted in a few model solutions (REFS in particular is bullish), will plaster low-end chance (20%) PoPs nearly continuously Tuesday and Wednesday (though keep in mind that equates to an 80% chance of dry conditions).

The hot and humid pattern looks to break down on Thursday as a stout upper-level shortwave "kicks" the aggregate Pacific troughing and and associated cold front eastward toward the Midwest. While the strongest upper-level flow looks like it will be displaced behind the cold front, seasonably strong low-level flow ahead of the front (925-700 mb flow increasing from 30 to 50 kt) within a strongly unstable airmass (MUCAPE > 3000 J/kg) does raise concern for an eastward-moving squall line with a threat for destructive winds in the general region. Temperatures and heat indices on Thursday will depend on the ultimate arrival timing of the front (our current forecast has it arriving during the evening meaning daytime hours may be hot and humid once again).

Borchardt

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 127 PM CDT Sun Jun 7 2026

Key Messages:

- Periodic shower and thunderstorm chances exist through most of the TAF period.

- MVFR ceilings are possible tonight into tomorrow morning.

A warm and humid air mass will promote shower and storm chances through much of the current TAF period as an upper-level disturbance pivots through the region.

For this afternoon, thunderstorms are likely in the 19Z to 21Z or so time window at RFD, where torrential rainfall will also likely reduce visibilities to IFR levels or lower for a brief period of time. Confidence in thunderstorms occurring at or in close proximity to the Chicago metro terminals through this evening is lower compared to RFD, but did introduce some targeted PROB30 groups for SHRA (TSRA for DPA) during the time frame when at least isolated shower activity is most likely to percolate close by. Broad isentropic ascent within this moist and unstable air mass may then permit some nuisance shower activity to persist in the area through much of tonight. There may be a period of time tonight where shower coverage could grow large enough to warrant something more than just a VCSH mention in the TAFs, but confidence in whether this will occur and where/when is low.

The early-mid morning tomorrow appears to be the most likely time frame for little to no shower/storm coverage across northern Illinois and northwest Indiana during the current TAF period. By the late morning or early afternoon, another wave of scattered showers and storms will develop, and the expectation is for this convection to persist through the afternoon. Gusty outflow winds associated with the most robust thunderstorms tomorrow (and really, today as well) may lead to erratic wind shifts, while torrential rainfall will also cause sharp visibility reductions.

Otherwise, easterly winds today will trend more southeasterly tonight into tomorrow morning, then more southerly tomorrow afternoon. At least patchy MVFR ceilings may also move into the area late tonight or early tomorrow morning. RFD stands the highest chance of seeing prevailing MVFR (or lower) ceilings, though some chance for them exists at the Chicago metro terminals as well.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

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