275
FXUS63 KLOT 080056
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
756 PM CDT Mon Jul 7 2025

.KEY MESSAGES...

- Dangerous swimming conditions continue at Lake Michigan
  beaches, but improving late this evening.

- Chance (30-50%) for scattered showers and thunderstorms on
  Tuesday across primarily northern and central IL.

- Low shower/storm chances continue on Wednesday. Better chances
  return Friday/Friday night.

&&

.DISCUSSION...
Issued at 226 PM CDT Mon Jul 7 2025

Tonight:

Expect partly cloudy skies and quiet conditions with seasonable
overnight lows in the lower to mid 60s outside of Chicago and
upper 60s in the city. The Beach Hazards Statement is set to
expire at 7pm for Illinois beaches and 9pm for Indiana beaches,
which looks reasonable per web cams and observations as of this
writing. There could be some patchy fog tonight near/south of
the Kankakee River overnight.

Castro


Tuesday through Monday:

Forecast evolution for Tuesday remains a bit unclear, with some
timing differences in the handling of low-amplitude disturbances
noted in today`s guidance. At the surface, a moist axis which is
currently displaced west of the Mississippi River will slosh
eastward into the region as low-level southwesterly flow returns.
Aloft, several vorticity maxima will be in the vicinity as a more
notable shortwave translates well to our north across the
Minnesota Arrowhead Region. Have expanded some 20-30 percent
PoPs a bit farther east across the region Tuesday morning as
very modest ascent within a moistening airmass could yield
clusters of showers and a few storms.

Through the rest of the day, upper 60s/near 70 degree dewpoints
are forecast to return, and most guidance commensurately
suggests capping will erode through the late-morning and
afternoon, even with muted insolation and the potential for
pockets of morning showers/storms tied to a 700 mb wave in the
region. While surface convergence isn`t strongly defined
tomorrow, the presence of a moist/destabilizing airmass and
presence of several disturbances aloft suggests mid-range chance
PoPs remain appropriate to cover the potential for afternoon
and early-evening shower and thunderstorms. Mid-upper flow looks
fairly weak, so storms should remain disorganized and posing
primarily a locally heavy rain and gusty wind threat.

Some potential that activity festers a bit through Tuesday
evening, but should see a gradual diminishing trend as drier
low-mid level air spreads in from the north. Through the day on
Wednesday, forecast soundings look like they become increasingly
capped across the northwest half of the region as a subsidence
inversion pushes eastward. Deeper boundary layer moisture is
evident with south and east extent through the area, however,
resulting in more limited capping. A lack of defined upper-level
features suggests that any diurnally-driven activity may remain
more sparse in coverage, and tied generally to surface
boundaries.

Speaking of boundaries (on Wednesday): today`s guidance is
starting to hit the wind response on the lake a bit harder as a
backdoor front drops down the lake, which conceptually fits the
set up of a near 1020 mb high pushing east across the UP of
Michigan. Gusty northerly wind response is not ubiquitous in the
model guidance today, but did boost winds a bit on the lake,
and will need to keep an eye on this window for a period of
moderate or greater swim risk.

Thursday could end up being largely dry in the wake of the
aforementioned front. The surface high won`t build across the
entire area, and lingering moisture could hold on in our far
southern locales, enough to justify hanging onto some very low
(15%) PoPs south of the Kankakee River vicinity, but even these
could end up being a bit too high.

On Friday-Saturday, forecast confidence begins to diminish as a
fairly sharp shortwave trough slicing across the Northern
Plains starts to interact with remnant MCVs/vorticity clusters.
Deterministic GFS continues to advertise some severe weather
threat across northwest Illinois but currently remains a bit of
a south and east outlier across the guidance suite.

Carlaw

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 756 PM CDT Mon Jul 7 2025

Key Messages:

- Chance for showers and thunderstorms tomorrow, though
  uncertainty remains regarding coverage and timing.


The main forecast concern for the terminals during this TAF
period is the potential for showers and thunderstorms as better
low-level moisture slides into the region. Overall, confidence
remains low on expected shower and thunderstorm trends into
tomorrow due to somewhat nebulous large-scale forcing, among
other things.

At RFD, couldn`t rule out some spotty shower activity
occurring nearby this evening, but the better chances for
showers should come tomorrow morning as the remnants of a
convective complex originating from the central/northern Plains
reach the area in a likely decaying state. There should be some
lower-end chances (20% or less) for thunder with this tomorrow
morning and again later on in the day with any new convective
development in the area (closer to 25-30%), but confidence in
these outcomes was just a bit too low to make any notable
changes to the inherited RFD TAF.

For the Chicago metro terminals, the remnants of the Plains
complex may arrive late on in the morning or during the early
afternoon, but initially drier air being in place at this time
should limit the likelihood of showers or thunderstorms
occurring during this time frame to just under 30%. Better
chances for showers and storms in the Chicago metro air space
should come later on in the afternoon during peak heating and as
the better low-level moisture finally arrives. The inherited
PROB30 groups for TSRA still appear to adequately highlight
this possibility amidst the existing uncertanties. Any
thunderstorms that do manage to develop during the afternoon
will have the potential to produce gusty winds and erratic wind
shifts.

Lastly, it`s also worth noting that a minority of model
guidance is suggesting that a lake breeze may produce an
easterly wind shift at ORD and MDW during the afternoon. While
such an outcome appears to be in play, it seems more likely that
southerly to southwesterly winds will be strong enough to keep
the lake breeze east of ORD and MDW, but trends in guidance will
need to be monitored.

Ogorek

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement until 7 PM CDT this evening for ILZ006-
     ILZ103-ILZ104.

IN...Beach Hazards Statement until 9 PM CDT this evening for INZ001-
     INZ002.

LM...None.

&&

$$

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