159
FXUS63 KLOT 221651
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1151 AM CDT Sun Jun 22 2025

.KEY MESSAGES...

- Dangerously hot and humid conditions will continue through at
  least Monday evening. A Heat Advisory remains in effect through
  Monday evening for the entire CWA except Cook County IL where
  an Extreme Heat Warning is in effect.

- The magnitude of heat should lessen by Tuesday, though heat
  indices will still be in the upper 90s to near 100 through
  much of the week. Heat headline extensions are not currently
  planned.

- Shower and storm chances increase incrementally Monday evening
  through the end of the week. Some may be severe with damaging
  winds and flash flooding.

&&

.DISCUSSION...
Issued at 327 AM CDT Sun Jun 22 2025

Through Monday:

Conditions are awfully warm out there early this morning. As of
around 3 AM, temperatures are still sitting in the upper 70s
and lower 80s around the area. Otherwise, skies are nice and
clear and marginally breezy southwest winds are gusting to 20 to
25 mph semi-frequently.

Very little has changed in our expectations for the second day
of this heatwave. Synoptically, the upper high responsible for
the heat will propagate from the TN Valley northeast into the OH
Valley during the day today lifting 500mb heights overhead to
an impressive 5960m! From a heat index standpoint, today should
feel very similar to yesterday. The consensus is pretty strong
among models that today should generally be just a couple of
degrees warmer than yesterday, from largely lower 90s to now
closer to middle 90s expected this afternoon. Conversely,
dewpoints look to mix out slightly lower than yesterday, into
the lower 70s as opposed to middle 70s. These sort of readings
should again yield afternoon heat indices between 100 and 105F,
possibly a little higher in spots.

Today will also be another breezy day, although not nearly as
windy as what we saw yesterday. Those aforementioned gusts that
we`re seeing are the result of a low level jet seated right off
the deck that we`ve been occasionally mixing into. This jet will
actually be weakening through the morning, but we`ll see gusts
at the surface pick up as mixing into the jet deepens. We`re
expecting gusts in the ballpark of 25 to 30 mph from late
morning into early evening mainly near and north of I-80 with
slightly lesser winds anticipated farther south. The gusts will
ease for the night before picking back up to 20 to 25 mph for
Monday.

Conditions will again remain warm during the night tonight with
lows forecast in the middle to upper 70s. Unless the forecast
proves several degrees too cool, it looks likely that Chicago
and Rockford will be breaking their warm low temperature record
for today, just as they both did for yesterday (see climate
section of AFD for details.)

The oppressive heat will continue into Monday. Temperatures are
expected to be a tad warmer than today with highs forecast to
make a run at upper 90s in a few spots. Slightly cooler midday
dewpoints in the upper 60s to around 70 degrees should produce
peak heat indices over 100 to around 105F. A rather sharp cold
front will approach the area from the northwest late Monday
afternoon, but unfortunately will not arrive in time to cool
things off during the day. More on this front and associated
rain and thunder chances can be found in the long term
discussion below.

Doom


Monday Night through Saturday:

The extended forecast period features a shift to a more active
pattern lead to episodic shower/storm chances and continued
warm and humid conditions.

Convection will likely be ongoing northwest of the area Monday
evening along a cold front extending across Iowa into southwest
Wisconsin. Instability is maximized along and south of this
boundary (MUCAPE >2000 J/kg), which combined with ~25-30kt of
effective bulk shear would be supportive of severe convection
capable of damaging winds and hail. The big question mark at
this time is how far southeast this activity can reach before
dissipating after sunset. Have maintained low chances (~20-30%)
generally near and north of a Dixon to Waukegan line, highest
northwest of Rockford, though it is quite possible the entire
area ends up dry. Nevertheless, remnant outflow winds could make
inroads across northern Illinois, resulting in a gusty
northwest wind shift and cooling things off a bit. The rest of
the area will remain warm and humid through Monday night with
lows still in the mid-upper 70s.

The upper level ridge responsible for the early week heat wave
begins to flatten out toward midweek with the baroclinic zone
(stalled surface boundary) setting up near and over the area. As
weak disturbances move within the mid-upper flow paired with
diurnal heating, expect regular shower and thunderstorm chances
through the end of the week. While the jet stream will remain
well north of the area at the top of the ridge (and with it the
better shear), ample instability south of the surface boundary
will still be supportive of strong to severe storms capable of
damaging winds. High PWATs and weaker flow aloft also suggest
there could be a localized flooding threat. There will be plenty
of dry hours but pinpointing when those occur remains low
confidence at this range. While warm and humid conditions likely
continue through the end of the week, it won`t be as oppressive
as experienced earlier in the week, with highs in the upper 80s
to lower 90s and heat indices in the 90s to locally near 100.
Onshore flow at times should help cool temperatures off near the
lakeshore.

Petr

&&

.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 1151 AM CDT Sun Jun 22 2025

Southwest winds will remain breeze through the TAF period, with
gusts in excess of 25k kt during the afternoon easing and
becoming more sporadic during the overnight hours. Otherwise,
there are no other aviation concerns.

Borchardt

&&

.CLIMATE...
Issued at 327 AM CDT Sun Jun 22 2025

Temperatures early this week will threaten record highs and
record warm lows for Chicago and Rockford. Here are the current
records:

Chicago              High       Warm Low
Sunday 6/22        97 (1988)    76 (1923)
Monday 6/23        97 (1930)    79 (1923)

Rockford             High       Warm Low
Sunday 6/22        97 (1923)    73 (1908)
Monday 6/23        97 (1923)    74 (1908)

NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory until midnight CDT Monday night for ILZ003-
     ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-
     ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ106-
     ILZ107-ILZ108.

     Extreme Heat Warning until midnight CDT Monday night for
     ILZ103-ILZ104-ILZ105.

IN...Heat Advisory until midnight CDT /1 AM EDT/ Monday night for
     INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 10 PM CDT this evening for the IL
     and IN nearshore waters.

     Small Craft Advisory from 8 AM to 9 PM CDT Monday for the IL
     nearshore waters.

&&

$$

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