textproduct: Chicago

KEY MESSAGES

- Wildfire smoke has again filled in over the region bringing hazy skies and poor air quality. An Air Quality Alert is in effect today.

- Hazardous swimming conditions will be found at southern Lake Michigan beaches through at least this morning and possibly stretching into the afternoon.

- Strong to severe thunderstorms will be possible Monday evening and night.

DISCUSSION

Issued at 321 AM CDT Sun Jul 19 2026

Conditions are nice and quiet out there early this morning with temperatures in the upper 60s and the occasional NE breeze. However, wildfire smoke really filled back in over the region late yesterday, especially toward the end of the evening when we saw AQIs start to tank around the area. Most readings out of NE IL and NW IN are now in the "unhealthy" category with a couple down in "very unhealthy" territory. Luckily, near-surace smoke concentrations are beginning to thin out again. Visibility observations have been trending upward these past few hours upstream to out east and northeast and a handful of sites around our area are already starting to see improvements as well, a few back up to 6+ miles from 3 or less earlier in the night. The improvements have also been noticeable on area webcams. Nonetheless, elevated AQIs are expected to remain throughout the day and the Air Quality Alerts around the area have been extended through today. Expect a hazy filter to our otherwise partly cloudy skies today that could potentially bleed into early tomorrow before clearing up further.

High temperatures this afternoon are forecast in the lower 80s away from the lake with 70s expected along and closer to the lakeshore. Speaking of the lake, waves are awfully choppy out there this morning following yesterday's cold front. While conditions will gradually ease through the day, hazardous swimming conditions will be present at area beaches through at least the morning hours, if not stretching into this afternoon. Accordingly, extended the going Beach Hazards Statement through 18Z today.

Water vapor satellite imagery depicts a defined circulation over British Columbia early this morning as a result of a Pacific trough that moved onshore yesterday. The trough base will gain some momentum as it works east across the US-Canadian border today before digging southward into the northern Plains and upper Midwest tonight and tomorrow. This feature will provide an opportunity for severe weather as it swings across the area late tomorrow.

A decaying shortwave will get swallowed up by the trough over the northern Plains later today and a cluster of thunderstorms is expected to result across upstream areas to our west and northwest late today through tonight. This dying wave will approach our area from the northwest during the day tomorrow. A previously stronger signal from models had some decaying showers and storms working into our area during the afternoon, but many have since backed off suggesting we won't see much of anything with this first wave. A big warm nose extending east across Mississippi during the day will greatly limit and cap instability which will hinder continued convection into IL. In the forecast, maintained some slights and low-end chances across our north and northwest during the afternoon where some remnant showers or a stray thunderstorm are most likely.

The severe potential will arrive in the evening and stick around through late tomorrow night as a strongly forced cold front passes through. As the base of the upper trough drops into Midwest late tomorrow, shear will quickly ramp up and the cooler midlevel air spilling into region will steepen up lapse rates and increase instability aloft. A veering 60+ kt effective shear profile is expected to work in ahead of the front. The big question that remains is the quality of low level instability during this time, especially following the morning wave, which will influence the severity of storms. Even if we see little to no precip during the day, remnant outflow boundaries and such may have a big influence on the low levels' ability to recover into the evening. A majority of camps have 1500-2500+ J/kg of MLCAPE regenerating ahead of the front for the evening. However, all available deterministic guidance resolves some degree of low level capping with elevated LFCs, some much more than others. It's very possible (if not likely) that the robust forcing can overcome what could be a somewhat nebulous cap and storms based near the surface will have much greater instability and shear to work with than any elevated convection. It might also be worth mentioning that there are a couple of camps out there, the HRDPS and MPAS-RRFS namely, that are more aggressive with daytime convection nearby and immediately upstream and don't allow the environment to recover sufficiently for DMC into the evening. While such an outcome is a big outlier among guidance, it's certainly a plausible one given the upstream environment and one that we will have to keep in the back of our minds as events unfold tomorrow.

There remains uncertainty in the timing and coverage of the potentially severe storms. They could work into our north as early as early evening, although more likely after late evening, and storms may not exit to our south until predawn Tuesday. Storm mode is unclear as well but the high CAPE/high shear environment could manifest a convective line with embedded supercells or severe bowing segments. The biggest concern is, by far, damaging to locally destructive winds. Severe hail will also be possible and long, looping low level hodographs would support a tornado threat to ML-based storms. Deep layer moisture with PWATs near 2" would also support periods of very heavy rain and perhaps some localized flooding issues, but the progressive nature of storms don't appear to pose a widespread flood threat. SPC's 06Z Day 2 Outlook expanded the wind-driven Enhanced Risk into our west and northwest CWA with a Slight Risk extending down to about the I-80 corridor.

There's quite the spread in temperature guidance for Monday with uncertainty in coverage of storms and cloud cover during the day. The forecast is calling for lower and middle 80s, but could end up being warmer. High pressure working into the region should keep conditions dry during the middle of the week. This will result in some gusty winds on Tuesday which will continue over the lake Tuesday night and hazardous swimming conditions are expected to develop on the lake for Tuesday night and Wednesday. Another seasonably warm day is expected on Tuesday before the high drops into the region and we get a brief spill of cooler air. Highs are favored in the 70s on Wednesday and back into the 80s for later in the week.

Doom

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1230 PM CDT Sun Jul 19 2026

No major forecast concerns are expected through this TAF period as high pressure will generally be in control. Lingering wildfire smoke will continue to result in 4-6 SM visibilities across northern IL and northwest IN through early evening before visibilities improve as smoke concentration diminishes. However, some smoke aloft looks to still result in some hazy skies through tonight. There is also a non-zero chance (<10%) for some patchy fog to develop after midnight near DPA and RFD, but with dew point depressions forecast to be above 5 degrees confidence on fog coverage is too low to include. Otherwise, expect east- northeast winds around 10 kts this afternoon to ease to around 5 kts overnight as they veer towards a south- southwest direction by daybreak Monday.

Heading into Monday, a complex of showers and thunderstorms is forecast to develop in MN tonight and dive southward towards northeastern IA and southern WI early Monday morning in a decaying state. The expectation is for this complex to dissipate prior to reaching northern IL which should allow dry conditions to prevail through the end of this TAF period. However, if this complex fails to develop or weakens sooner than forecast then conditions may become sufficient to result in some scattered thunderstorms Monday afternoon. Since confidence on this occurring is very low have opted to maintain a dry forecast, but will continue to monitor trends closely. Regardless, the southwest winds Monday will increase during the afternoon ahead of a cold front with gusts peaking in the 20-25 kt range.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

IL...Air Quality Alert until midnight CDT tonight for ILZ003-ILZ004- ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019- ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104- ILZ105-ILZ106-ILZ107-ILZ108.

Beach Hazards Statement until 4 PM CDT this afternoon for ILZ006-ILZ103-ILZ104.

IN...Beach Hazards Statement until 4 PM CDT this afternoon for INZ001-INZ002.

Air Quality Alert until midnight CDT /1 AM EDT/ Monday night for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...None.