387
FXUS63 KLOT 191101
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
601 AM CDT Sun Jul 19 2026

.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 /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 601 AM CDT Sun Jul 19 2026

The only real concern from an aviation perspective is modestly
reduced visibility in smoke. Experimental HRRR smoke guidance
does suggest visby should gradually improve throughout the day,
but will take the pessimistic route and advertise 6SM through
00Z. If visbys exceed 6SM for more than an hour or two, figure
an AMD can be issued to clean things up. Otherwise, winds should
generally be out of the northeast today before becoming nearly
calm tonight and southwesterly toward the very end of the TAF
period.

Borchardt

&&

.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 1 PM CDT this afternoon for
     ILZ006-ILZ103-ILZ104.

IN...Beach Hazards Statement until 1 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...Small Craft Advisory until 10 AM CDT this morning for the IL
     and IN nearshore waters.

&&

$$

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