189
FXUS63 KLOT 162316
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
616 PM CDT Wed Jul 16 2025

.KEY MESSAGES...

- Scattered to numerous thunderstorms into the early evening
  from the Chicago metro and points south and east. There is a
  level 2/5 severe weather risk for most of the area with
  damaging winds as the primary severe weather hazard.

- MUCH cooler and less humid Thursday with gusty northerly winds
  and dangerous swimming conditions at Lake Michigan beaches.

- Periods of warmth, humidity, and thunderstorms expected this
  weekend into early next week, followed by an increasing signal
  for potentially dangerous heat arriving mid next work week.

&&

.DISCUSSION...
Issued at 309 PM CDT Wed Jul 16 2025

Tonight:

After the strong to severe storms end early this evening in the
wake of the cold front, the southward progress of the outflow-
augmented front will slow. A strengthening low-level jet
overriding the boundary could foster the development of training
convection just to its north. This could include areas roughly
near and south of US-24 if the boundary stalls just south of the
CWA. Most of the latest guidance brings the front far enough south
to result in a scenario with training convection with torrential
downpours and an associated flood threat into areas near and south
of US-24 as a less likely outcome at this time (but still
certainly one worth monitoring for). Aside from this low-end
potential, cooler air will filter into the area from the north
behind the front with lows down into the 60s near and northwest of
I-55.

Thursday through Wednesday:

As alluded to above, fairly strong high pressure (~1020mb) for
mid- summer combined with push from earlier convection should send
the composite outflow boundary/cold front south of our area
Thursday. In the wake of the front, look for much cooler and less
humid air to filter into the region. Morning stratus should break
up into a scattered to broken stratocumulus deck during the
afternoon, with this cloud cover likely aiding in keeping temps
cooler. Thursday afternoon temps should be around 20F cooler in
the Chicago area with readings in the low to mid 70s with a brisk
(for July) wind off the lake. That brisk wind off the lake will
also help build up larger waves and lead to hazardous/dangerous
and potentially life-threatening swim conditions at unprotected
Lake Michigan beaches Thursday into Thursday night. A Beach
Hazards Statement will be issued for this, in effect into early
to mid Friday morning.

Friday will be warmer, but with still comfortable humidity
levels. Boundary that will have pushed south of our area
Thursday should stall near the Ohio River before heading back
north as a warm front Friday night into Saturday. There`s been a
pretty consistent signal in bringing a convectively enhanced
shortwave across the region later Friday night into Saturday.
Still several days out, so exact timing of this feature and
where exactly it tracks may need to be refined in coming days,
but the general idea of an MCS moving across the mid-Mississippi
Valley in this time frame, possibly affecting portions or all
of our area, continues.

Medium range guidance has trended toward slightly more
amplified northern stream troughing over the Great Lakes into
New England later in the weekend. This would allow for a
transient surface high pressure to move across the Great Lakes
Sat night into Sunday. This, combined with the prior MCS, could
push the effective boundary and rain/storm chances south of our
area. Confidence is too low to significantly reduce or remove NBM
POPs for Sunday, but there is an increasingly plausible scenario
where the second half of the weekend could end up dry and a bit
cooler and less humid, particularly near and north of I-80.

Looking ahead to the first half of next week, there continues to
be a consistent signal in medium range guidance that a strong
upper level ridge and associated dome of heat will build over
the central and eastern portions of the nation. In this time
frame, we`d expect that the front that pushes southward some
Sunday will lift back north bringing the potential zone of MCS
activity with it back into our area for a time early next week.

By the middle of the week, the upper ridge is progged to become
anomalously strong and centered over the lower and middle
Mississippi Valley. Assuming MCS activity doesn`t significantly
impede the northward movement of the boundary, our area could
get into a bout of some potentially dangerous heat during the
middle and end of next week. Operational runs of the GFS and
ECMWF both are explicitly forecasting 80F+ dewpoints
accompanying the heat, which given we`ll be in the heart of
evapotranspiration season, may not be unreasonable. Still plenty
of uncertainty regarding if convection can temporarily impede
the northward building heat, but concern is growing that
potentially dangerous heat wave could develop next week in or
near our area.

- Izzi/Castro

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 616 PM CDT Wed Jul 16 2025

Aviation forecast concerns for 00Z TAFs:

- Breezy WSW winds gusting to 25 kts eventually becoming NW
  later this evening before diminishing. Winds turn northeast
  midday Thursday.

- MVFR ceilings developing later tonight and persisting
  Thursday before lifting to VFR late in the afternoon.

- Spotty SHRA along IL/WI border this evening, mainly near RFD.

Line of thunderstorms has pushed well east of the terminals
early this evening. A few lingering showers along the IL/WI
border will track near RFD early, though no additional TSRA are
expected (TS threat <10%).

Surface low pressure was analyzed over southeast WI as of 23Z,
in association with a compact mid-level disturbance tracking
east toward Lake Michigan. Surface winds are expected to become
breezy from the west-southwest this evening south of the low,
turning northwest late this evening/overnight in association
with a trailing cold front. Gusts around 25 kt are expected
before winds eventually diminish later tonight. Surface winds
should eventually turn more northerly into Thursday morning,
before turning northeast midday.

As low-level winds become more northwest to north tonight,
extensive area of MVFR ceilings currently over MN/WI is expected
to spread across the terminals. These look to linger into
Thursday before gradually lifting to VFR later in the day.

Ratzer

&&

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

     Beach Hazards Statement from Thursday morning through Friday
     morning for ILZ006-ILZ103-ILZ104.

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

     Beach Hazards Statement from 4 AM CDT Thursday through Friday
     morning for INZ001-INZ002.

LM...Small Craft Advisory from 9 AM Thursday to 4 AM CDT Friday for
     Winthrop Harbor IL to Gary IN.

     Small Craft Advisory from 4 AM Thursday to 4 AM CDT Friday for
     Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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