057
FXUS63 KDVN 211031
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
531 AM CDT Thu Aug 21 2025

...Updated for 12z Aviation...

.KEY MESSAGES...

- Fog potential late tonight/early Friday AM.

- Largely a dry forecast, outside of a chance (20-40%) for
  precipitation for parts of the area Friday night/Sat.

- The rain chance is ahead of a stronger cold front, which will
  bring a reinforcing shot of cool air and a Fall preview
  Sunday through Tuesday. CPC favors these below normal
  temperatures sticking around through the end of the month.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 300 AM CDT Thu Aug 21 2025

Surface and upper level ridging will remain the dominant features
through the day on Friday, and will keep us largely dry
(precip chance <10% this afternoon NW IL) and rather nice with
humidity levels trending down. Some stratus clouds may develop/
advect into parts of the area this morning followed by some diurnal
cumulus, but still ample sunshine with highs in the upper 70s to
lower 80s.

Tonight, we are likely looking at a decent radiational cooling
setup with clearing skies and near calm winds. This will allow
lows to drop back into the upper 50s to lower 60s. In addition,
as cross-over temperatures are breached we`ll see the potential
for fog. Some of the fog could be dense with NBM probabilities
for < 1 mile visibility at 15% to 25%. The HREF probabilities
for < 0.5 mile visibility are generally 35% to 50% with some pockets
of 60%.

Friday, we`ll see the surface ridge begin to gradually sink to the
south. Correspondingly winds will shift to the west/southwest
albeit still fairly light, but with more in the way of sunshine
highs should nudge up closer to normal in the lower to mid 80s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 300 AM CDT Thu Aug 21 2025

Late in the day Friday into Friday evening, clouds will start to
increase ahead of an approaching shortwave and cold front.
Stronger instability and deep layer shear look to reside to our
northwest where SPC has outlooked a large Marginal Risk (Level 1
of 5) from NE/SD through nw 1/2 of IA into MN/WI. CAMs are in
nearly unanimous agreement on this activity weakening as it
approaches, outpacing the instability and deeper moisture axis,
but will keep chances for showers (20-40%) Friday night and
possibly into Saturday AM with the highest chances across our
north/west service area. Can`t totally rule out some lightning,
and this potential will largely be tied to timing of when the
convection weakens.

In the wake of this frontal passage on Saturday, northwest flow
will usher in a period of below normal temperatures Sunday
through Tuesday. Highs looks to be in the mid 60s to lower 70s
and lows in the 40s to lower 50s. Some record lows are a
possibility Monday morning, and especially Tuesday morning when
the high settles into the region to promote more widespread lows
in the 40s. After this very humid and warm Summer it`s sure to
feel like Fall! Definitely a period to give the AC a much needed
break. Of course in the cyclonic flow we`ll have to be watchful
for a few showers, but right now confidence is too low for mention
with the better precipitation signal favoring the Great Lakes region.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 525 AM CDT Thu Aug 21 2025

E/NE flow with some moisture off Lake Michigan and diurnal heating
with promote generally SCT-BKN MVFR to VFR cloud bases and
occasional ceilings today. There is a chance (30%) for a period of
IFR ceilings at DBQ this morning, with IFR currently expanding
through southern WI and north-central IL immediately downstream
of Lake MI. Otherwise, DBQ could also see some variable and rapid
visibility fluctuations in fog at the start of the period, with
near calm winds and mainly clear skies in between some departing
high MVFR/low VFR stratus and slow approaching low stratus in WI/IL.
Tonight may offer better radiational fog setup with clearing skies
and light winds. Have gone with IFR to MVFR visibilities at the TAF
sites 06z-12z Friday. There is potential though for areas of LIFR/
VLIFR in dense fog with 00z HREF probabilities of <0.5 mile at 35-50%.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.

&&

$$

SHORT TERM...McClure
LONG TERM...McClure
AVIATION...McClure