422
FXUS63 KLOT 081130
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
630 AM CDT Sat Aug 8 2026

.KEY MESSAGES...

- An active weather pattern will get underway on Sunday with
  periodic thunderstorms forecasted through at least the middle
  of the upcoming week. Some storms could be severe and may also
  result in flash flooding, especially on Sunday and Monday.

&&

.DISCUSSION...
Issued at 330 AM CDT Sat Aug 8 2026

Through Tonight:

A regional surface analysis taken at 0800Z depicted a cold
front extending from just east of Wisconsin`s Door Peninsula
southwestward towards the Quad Cities. This front will continue
to drift southeastward through the remainder of this morning
before stalling out across central Illinois and Indiana this
afternoon. Sufficient low/mid-level moisture has resulted in the
presence of an elevated modestly unstable layer rooted near
800-850 mb along and ahead of the front, and isentropic upglide
has taken advantage of that to support the presence of isolated
showers and a few storms across the frontal zone. This already
sparse convective coverage should diminish further over the next
few hours as the magnitude of the ongoing isentropic ascent
weakens with time, so will carry slight chance PoPs through a
little past sunrise to account for any festering isolated
shower/storm activity near the front.

Also monitoring the potential for fog this morning -- primarily
across our southern counties, where a few AWOS sites have
already reported some visibility reductions. Think that the
mid- and high-level cloud cover ahead of the front should be
able curtail things enough to keep the fog from getting too out
of hand and prevent a repeat of yesterday morning`s dense fog,
but will continue to monitor observational trends closely.

Most, if not all, of our forecast area should find itself north
of the aforementioned front come mid-afternoon and along the
northern periphery of a surface ridge. As a result, dry
conditions with more comfortable humidity levels should be
experienced today -- particularly with northward extent --
amidst primarily low-mid 80s high temperatures. Mid-upper 70s
highs are forecasted in the immediate vicinity of Lake Michigan,
where a lake breeze is expected to sharpen by early this
afternoon. Skies today should be mostly clear outside of any
diurnal cumulus, though they could have a milky look to them
later on in the day as smoke originating from wildfires in the
Pacific Northwest spreads over the area once again.


Sunday through Friday:

Tomorrow, the stalled frontal boundary will lift back northward
as a warm front, ushering evapotranspirationally-enhanced 70s
dew points back into the area. The return of this muggy air mass
will set the stage for a prolonged, convectively active period
of weather across the region that will begin on Sunday and
continue well into next week. However, confidence in forecast
specifics regarding the thunderstorm potential during this
period inherently remains low given the involvement of a muggy
summertime air mass and subtle forcing mechanisms, as well as
the influence of one convective cycle on the next and the
subsequent domino effects that follow.

The initial wave of convective activity that we`ll need to keep
an eye on will develop well to our west and northwest tonight
as a shortwave ripple embedded within stout west-northwesterly
flow aloft acts upon the northeastern periphery of the inbound
EML plume. It`s not yet clear at this time whether this activity
will evolve into an MCS or whether it will remain disorganized
as it propagates towards the east-southeast. At any rate, this
activity could reach northern Illinois as early as Sunday
morning, so that is when mentionable PoPs and thunderstorm
chances are first introduced into our going forecast. The
influence of this initial round of convection and the associated
cloud debris on destabilization efforts puts into question
where and when additional convection may develop later on in the
day on Sunday.

Assuming that the air mass that will be in place doesn`t get
convectively overturned to a significant degree by this initial
activity, a strengthening low-level jet and another subtle
shortwave diving into the Midwest suggest that storms are likely
to redevelop somewhere in the general region late Sunday
afternoon or evening. With northern Illinois and northwest
Indiana appearing to be favorably positioned relative to these
atmospheric features, would think that it is more likely than
not that we`ll see some degree of thunderstorm activity across
our forecast area in this late day through Sunday night time
frame, so have largely kept the higher PoPs brought in by the
NBM for this time period. While the specific details regarding
Sunday`s thunderstorm threat remain uncertain, increasing
instability and strengthening deep-layer wind shear will support
the potential for severe thunderstorms with damaging winds and
hail. The moist air mass will also support torrential rainfall
rates with any storms, so some threat for flash flooding could
also materialize somewhere in the region.

With the muggy air mass and primary frontal zone not likely to
budge much by Monday, Monday will similarly be a day that will
be favorable for thunderstorms with threats for severe weather
and flash flooding in the region. Forecast specifics for Monday
are even less clear than the muddled picture for Sunday, owing
to its dependence on how Sunday`s convective cycle plays out
and where any surface boundaries get laid out. It`s then rinse
and repeat for Tuesday, and possibly Wednesday as well, as
additional shortwave disturbances are expected to zip into the
region and generate additional rounds of convection within the
relatively stagnant moist and unstable air mass.

With time, this air mass and the associated active quasi-
stationary frontal zone should eventually get suppressed
southward and relegate the thunderstorm activity to our south
along with it. Ensemble guidance suggests that this could happen
as early as Wednesday, but it`s more likely to take until
Thursday or Friday for this happen.

Ogorek

&&

.AVIATION /12Z TAFS THROUGH 18Z SUNDAY/...
Issued at 630 AM CDT Sat Aug 8 2026

Key aviation forecast messages for the 12Z TAFs:

- Patchy MVFR possible early this morning, though coverage
  appears lower than previous forecasts.

- Lake breeze turns winds NE at GYY midday and likely for MDW
  mid-afternoon. Low confidence in a wind shift at ORD.

- SHRA/TSRA chances return later Sunday morning/midday. Low
  confidence in timing and coverage prior to end of current
  ORD/MDW 30 hour forecasts.

Surface cold front was roughly from MKE to MLI at issuance time,
and will push through the Chicago metro terminals in the next
couple of hours. Winds will turn northwest with speeds around 10
kts behind the front. While patchy MVFR clouds can`t be ruled
out through mid-morning, GOES IR satellite imagery depicts lower
coverage of clouds than earlier expected and thus have pulled
MVFR ceiling mentions from TAFs.

High-res model runs continue to indicate lake breeze winds will
turn northeast at GYY around midday, and likely at MDW by mid-
afternoon. Guidance remains in decent agreement that the
boundary will remain east of ORD however, with winds remaining
northwest there until winds turn light south-southeast at all
sites after sunset this evening as weak surface high pressure
slides across the area.

Moisture/instability returns Sunday as winds turn south-
southwest and become somewhat breezy during the morning. It`s
likely there will be thunderstorm development late tonight
across parts of IA/MN/WI on a southwesterly low-level jet, and
some of this may approach the Chicago terminals toward the very
end of the current ORD/MDW 30-hour forecasts. Confidence is low
enough with the coverage and timing however to leave out of the
forecast at this time, though would expect some mention of
SHRA/TSRA by midday with later forecasts.

Ratzer

&&

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

&&

$$

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