099
FXUS63 KLOT 021953
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
253 PM CDT Sat Aug 2 2025

.KEY MESSAGES...

- Wildfire smoke may bring a return of hazy conditions and
  modest visibility reductions along with deteriorating air
  quality on Sunday

- Warmer and more humid conditions will return during the
  upcoming work week into next weekend, though thunderstorm
  chances appear they will remain muted.

&&

.DISCUSSION...
Issued at 253 PM CDT Sat Aug 2 2025

Tonight through Monday:

Expansive surface high pressure will remain centered over the
Great Lakes region, continuing the dry and comfortable theme of
the past few days. The only real item of note is the batch of
wildfire smoke over Wisconsin and Michigan evident on visible
satellite imagery and corresponding with modest visibility
reductions.

Tonight will be quiet, mostly clear, and seasonably cool with
lows in the 50s outside of Chicago. By tomorrow (Sunday) morning,
recent HRRR near-surface smoke concentration forecasts depict
elevated concentrations drifting southwest from near Lake
Michigan in Indiana back west-southwest across northern Illinois
and portions of central Illinois. Opted to include haze vs.
areas of smoke in the forecast with current trends suggesting
the smoke not being quite as much of an issue as this past
Friday. With this being said, the air quality should deteriorate
back down to at least unhealthy for sensitive groups levels
(orange AQI). Air Quality Alerts were again extended through
Sunday evening. Unless the smoke is thicker and limits
insolation more than expected, temps on Sunday should top out at
near 80F/lower 80s inland of Lake Michigan and upper 70s along
the lakeshore due to modest lake breeze cooling.

Maintained haze in the gridded forecast through Sunday night,
with uncertainty regarding how much near-surface smoke lingers
into Monday. Low temps should be at least a few degrees milder
Sunday night, followed by near seasonable highs in the lower to
mid 80s away from the lake on Monday afternoon, and then lows in
the 60s Monday night.

Tuesday through Saturday:

Dew points may uptick modestly on Tuesday along with a bit more
mid-level moisture. With a very weak mid-level impulse forecast
to drift east-northeast during peak heating (highs in the 80s),
there might be enough instability (albeit with 6C/km or less
mid- level lapse rates) to touch off a few isolated diurnally
driven thunderstorms. Favored zones for any isolated convection
(15-20% chance) would be near/south of I-80 and inland of the
lake breeze in Illinois.

The mid and upper level pattern looks to remain fairly blocky
and thus benign along with synoptic east-southeast winds from
high pressure over the Great Lakes the rest of next week.
General mid-level height rises back to or above 590 DaM at 500
mb and warming 850 and 925 mb temps points towards temps
returning to solidly above normal Wednesday and beyond, with at
least localized 90F highs Thursday- Saturday aside from any
modest Lake Michigan shoreline cooling. If the blockier pattern
holds like some ensemble guidance suggests, primarily dry
conditions will prevail, though can`t completely rule out
isolated diurnal convection on some of the days. If the pattern
breaks down quicker, which seems like a less likely outcome at
this point, then that would open the door to higher convective
chances next weekend.

Castro

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1208 PM CDT Sat Aug 2 2025

A surface high pressure system remains parked over the Great
Lakes. East to northeast winds this afternoon will once again
become light and variable overnight, before becoming east
northeasterly again after daybreak tomorrow. Experimental HRRR
smoke model output depicts another plume of near-surface smoke
arcing into northern Illinois and northwestern Indiana tomorrow,
with concentration values consistent with 2 to 4 mile
visibility. For now, will introduce 6SM HZ in all TAFs starting
at 15Z in favor of letting later shifts evaluate visibility
observations upstream (Michigan) to inform adjustments in later
forecasts.

Borchardt

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Air Quality Alert until midnight CDT Sunday night for ILZ005-
     ILZ006-ILZ012-ILZ013-ILZ020-ILZ021-ILZ103-ILZ104-ILZ105-
     ILZ106-ILZ107-ILZ108.

IN...Air Quality Alert until midnight CDT Sunday night for INZ001-
     INZ002-INZ010-INZ011.

LM...None.

&&

$$

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