338
FXUS63 KLOT 292324
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
624 PM CDT Wed Jul 29 2026

.KEY MESSAGES...

- Rain expected to develop during the day Friday and continue
  into Friday night before ending Saturday. Widespread rainfall
  totals over an inch are possible.

&&

.DISCUSSION...
Issued at 216 PM CDT Wed Jul 29 2026

Surface analysis early this afternoon exposes a center of high
pressure over central Lake Michigan. This high is responsible
for the dry weather and largely sunny skies today. It`ll keep
conditions quiet through tomorrow before ejecting to the east
clearing the way for our next rain chances. Another seasonably
warm day is expected tomorrow with highs forecast in the lower
and middle 80s. Tomorrow will again be mostly sunny, but high
level clouds will start moving over later in the day ahead of
this next storm system.

A midlevel shortwave disturbance is churning some showers over
the Intermountain West this afternoon. Over the next 36 hours or
so, this wave will sharpen up considerably, evolving into
closed mid level low by early Friday as it works into the
Midwest. Widespread showers are expected to blossom around the
deepening surface low over the northern Plains tomorrow and
track southeastward into our general vicinity on Friday. There
is fair agreement on the onset of rain in our west being late
morning to early afternoon, and into Chicago during the
afternoon hours. Widespread rain is then favored around the CWA
Friday evening into early Saturday. There remains some
uncertainty in trends through the rest of Saturday, but coverage
should wane through the day generally from north to south. Most
of the area looks to be dry by Saturday evening, maybe a bit
earlier across much of Chicagoland. Where global guidance had
previously had this closed low becoming cutoff and meandering
about the lower Midwest early next week, now the favored signal
is for the system to get sheared off to the northeast on Sunday.
While a few lingering showers still appear possible on the
backside of the low, mainly around the southern/southeastern
CWA, precip potential for Sunday is on a downward trend.

Still not expecting much in the way of embedded thunder
coverage with such cool low level air greatly limiting
instability through the column. Some embedded storms will be
possible, certainly, with some instability around and a strong
forcing. There`s some uncertainty regarding the track of the low
and, while its still favored to track south of the CWA, a
farther north track is still on the table. The NAM, UKMET, and
RRFS are all farther north with the track and, perhaps more
notably, the position of the effective warm front and northern
extent of the more supportive instability. This is due to these
camps resolving a deeper, more tightly wound upper low. If such
a solution were to verify, this would boost embedded storm
chances for areas that end up south of the warm front, though
still not seeing a signal for anything too strong or severe in
that case. There is concern, however, from a heavy rain
perspective. Deep saturation with seasonably high PWATs just
under 2" in conjunction with deep, dynamic forcing could result
in periods of heavy, soaking rainfall. A widespread 1"+ of QPF
through Saturday has been a consistent signal among
deterministic camps and WPC has the area in a slight risk (2 of
4) for excessive rainfall.

Conditions will be slightly cooler this weekend with the storm
nearby. Daily highs are forecast in the middle 70s to lower 80s,
likely coolest all around on Saturday. Gusty northerly winds
may develop on Sunday, especially down the lake, as a high
encroaches from the north which may produce choppy waves and
dangerous swimming conditions. A steady warmup is progged for
next week with largely quiet conditions favored through the
early part of the week.

Doom

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 624 PM CDT Wed Jul 29 2026

Aviation forecast concerns for the 00Z TAFs:

- Patchy ground fog away from the core Chicago terminals early
  Thursday morning.

- Weak southeasterly lake breeze wind shift possible at MDW and
  ORD late Thursday afternoon, though it may only approach and
  not move through both sites.

Surface high pressure was centered just north Milwaukee this
afternoon, and will drift southeast across the area overnight
and Thursday. This will result in our current modest northeast
winds becoming generally light and variable later this evening,
and light southwest (though perhaps still variable in spots)
during the day Thursday. A weak lake breeze is expected to
develop, though various high-res guidance shows some spread in
just how far inland it reaches with some (HRRR and some of the
GLAMP) guidance suggesting it will move through ORD and MDW
while others (RAP, etc.) do not. Can`t rule out the more
aggressive scenario, though have held off adding for now with
these boundaries sometimes struggling within the center of the
surface ridge. If it does affect ORD/MDW, it would likely be
late afternoon/toward evening with a modest SE to ESE direction.

Only other item of note is the potential for patchy ground fog
toward daybreak away from the core Chicago metro sites. Here
too, guidance shows a range of visibility impacts manly for
RFD/DPA. Forecast soundings indicate moisture is quite shallow
though with otherwise good radiational conditions with clear
skies and light/calm winds. Thus have maintained tempo mentions
for MVFR vis in fog for RFD/DPA, and we`ll have to monitor for
any potential lower conditions through the night.

Ratzer

&&

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

&&

$$

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