Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

463
FXUS63 KLOT 131111
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
611 AM CDT Wed Aug 13 2025

.KEY MESSAGES...

- Uncomfortable heat and humidity will return this weekend with
  heat indices 95 to 105 degrees.

- Shower and storm chances continue early next week.

&&

.DISCUSSION...
Issued at 313 AM CDT Wed Aug 13 2025

Through Thursday:

Some shallow/patchy fog will be possible early this morning,
with things quickly mixing/scattering out through mid morning.
Surface high pressure will build in across Iowa today, and we`ll
be on the eastern periphery of its influence this afternoon.
Forecast soundings reveal subsidence warming and drying taking
place in the 700-600 mb layer, while boundary layer moisture
beneath this inversion remains respectable, particularly south
of I-80. The HRRR once again looks like it`s probably mixing
dewpoints out a bit too much today, with the rest of the
guidance suite indicating surface Tds hanging out in the upper
60s/near 70 which should yield 1000 J/kg or so of diurnally-
increasing surface CAPE. Large scale forcing is weak, but a
sharpening lake breeze and modest DCVA associated with a 700-500
mb shortwave will be present today. Suspect that building most
cumulus will remain pretty flat, but some additional vertical
growth appears possible near the lake breeze and south of I-80
within the deeper reservoir of BL moisture. Have added in a
mention of sprinkles with PoPs generally less than 15 percent
this afternoon. Tonight into Thursday morning, some additional
patchy fog can`t be ruled out with light winds and clear skies.

Temperatures today and Thursday will be in the low to mid 80s,
with lake cooling holding highs in the upper 70s lakeside.

Carlaw


Thursday Night through Tuesday:

Thursday night into Friday, a broad upper ridge will spread
into the Midwest from the Plains driving upper height rises
across the region. Meanwhile, surface winds will turn southerly
ahead of an upstream synoptic wave advecting a warm airmass into
the region. As a result, Friday should be a few degrees warmer
than Thursday with highs forecast in the middle and upper 80s.
Continued warm advection into the weekend should pull highs into
the lower 90s on Saturday. While there`s some uncertainty in
afternoon dewpoints with the potential to mix into some pretty
dry boundary layer air, heat indices could exceed 100 degrees
around a majority of the CWA, maybe even nearing 105 in spots.

Ahead of that aforementioned wave out in the Plains, a highly
unstable airmass will overspread the western Midwest with
guidance resolving over 5,000 Joules of MUCAPE west of the
Mississippi Friday afternoon. Up to a few thousand Joules may
spread into our western CWA. But guidance is in very good
agreement that forcing and moisture will be too heavily lacking
nearby to hold out much hope for convection. Similar story for
Saturday; a baroclinic zone/frontal boundary will drape across
the upper Midwest along the northern periphery of the upper
high. South of that front, a few to several thousand J/kg of
uncapped, or only weakly capped, MLCAPE will build over the area
for the afternoon. Chances for convection look rather high
across WI along that front during the day. But that upper high
should do well to keep all noteworthy synoptic features away
from the local area making it difficult to anticipate convection
on Saturday despite the instability. Our best shot for storms
on Saturday will be across our north with any outflow pushing
south out of WI, but ensemble probabilities for precip during
the day are low.

There seems to be even less model agreement than in recent days
on the evolution of this front, any subsequent waves, and how
that`ll all interact with the upper high during the early part
of next week. The surface front may try to sneak across our CWA
on Sunday, perhaps as a composite outflow boundary, but the true
effective baroclinicity could get hung up to our north. This
front generally looks to meander about the region through at
least Tuesday. The airmass around and south of the front will
remain highly unstable keeping scattered convective chances
going all the while. The discrepancies in model QPF resulted in
broad-brush chance PoPs from the NBM during the Sunday through
Tuesday period. Conditions should quiet down again for the
middle of next week with high pressure looking to build in from
the north.

These uncertainties are impacting temperature expectations for
early next week as well. Depending on the the evolution of the
front, Sunday could also be uncomfortably hot with highs again
in the 90s and around 100 degree heat indices. This appears to
be the favored outcome, but there is a fair amount of spread
even within individual ensemble systems. Monday could be
similarly hot, but uncertainties continue to grow into the week.

Doom

&&

.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 611 AM CDT Wed Aug 13 2025

There are no major weather concerns for the 12Z TAF period.

Light NNW winds early will go NE at the Chicago sites and GYY
as a lake breeze moves inland. Some uncertainty in timing, but
around 16Z is a favorite among guidance for the Chicago sites,
and magnitudes should remain largely below 10 kt. Additionally,
can`t rule out a light shower or sprinkle around Chicagoland
this afternoon.

Doom

&&

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

&&

$$

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