277
FXUS63 KLOT 111845
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
145 PM CDT Sat Jul 11 2026

.KEY MESSAGES...

- Hot and humid conditions are expected much of the upcoming
  work week.

- Daily lake breezes should provide at least some relief near
  the lake during the afternoons Sunday through at least
  Wednesday.

&&

.DISCUSSION...
Issued at 145 PM CDT Sat Jul 11 2026

Low amplitude mid-upper level ridging over the western half of
the country is progged to amplify significantly while expanding
eastward. There is strong model agreement in developing an
anomalously strong mid-upper level ridge from the northern High
Plains east into the upper Great Lakes the first half of the
upcoming work week. By Tuesday-Wednesday, 500mb heights near the
center of this massive ridge could exceed 600dam. The core of
the potentially record breaking heat with this upper ridge is
expected to largely remain just to our north and northwest,
however, our area should be in close enough proximity to this
massive heat dome to see our own share of heat and humidity this
week.

Temperatures should be several degrees warmer Sunday,
particularly southern CWA where cloud cover today is holding
temps back a bit. Full or nearly full sunshine is expected
tomorrow through the middle of the upcoming work week. As the
upper ridge strengthens and expands eastward, look for
gradually building heat. By Monday afternoon, 925mb temps are
progged to warm to 23-27C, highest northern CWA. This should
support high temps ranging from the mid-upper 80s toward central
IL to the lower 90s north of I-80.

The hottest temperatures of the upcoming heat look to be Tuesday
into Wednesday when the strength of the ridge is expected to
peak. Both afternoons should feature high temps in the lower to
middle 90s. Worth noting that the GFS and ECMWF both seem to be
struggling with over-mixing and overly warm temperatures over
the urban areas, in some cases 5-10F warmer than nearby less
urbanized areas. While it will likely be a bit warmer in Chicago
urban heat island, the raw 2m temps in the GFS and ECMWF appear
unrealistically hot and have largely been discounted.

Synoptic flow will allow for afternoon lake breezes to form
tomorrow through Wednesday, which should provide some heat
relief for areas closer to Lake Michigan. Lake Michigan water
temperatures are running much above average and which should
limit magnitude and inland extent of lake cooling.

Finally, probably one of the bigger wildcards for this upcoming
heat will be the dewpoints. The strong upper ridge and
subsidence should result in a noteworthy inversion which could
limit the depth of mixing and ability for dewpoints to mix out.
We are entering the climatological peak of evapotranspiration
(ET), so even though low level flow will not be originating
from the Gulf, nearly full sunshine and relatively weak low
level flow should result in substantial evapotranspiration. The
NAM model tended to perform best with temps and dewpoints with
the late June heat wave and have trended our temp/dewpoint
forecast closer to the NAM Monday and Tuesday. Certainly
plausible that given the lack of added Gulf moisture and the
more shallow depth of the ET driven low moisture that dewpoints
may indeed mix out. Confidence in the forecast dewpoints and
resultant heat indices is lower than average for the upcoming
heat wave.

Upper ridge is expected to begin to gradually weaken toward the
of the upcoming work week and into next weekend, likely being
replaced with more of a northwest flow. Weaker capping and the
potential for subtle low amplitude disturbances riding the
northwest flow into our region certainly opens the door to at
least some threat for showers/storms by Friday into next
weekend.

- Izzi

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1220 PM CDT Sat Jul 11 2026

There are no key concerns to highlight for the 18Z TAF period.

NE winds around 12 kt may occasionally gust as high as 20 kt
this afternoon before subsiding this evening. Direction will
hold at NE into Sunday with near or below 10 kt expected through
the day. Expect VFR throughout the period.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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