540
FXUS63 KDVN 212335
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
635 PM CDT Thu Aug 21 2025

.KEY MESSAGES...

- There remains potential for at least patchy fog tonight through
  early Friday AM.

- A dry forecast is largely in place, with very pleasant
  temperatures from Sunday onward. The only chance for rain
  (20-40%) is late Friday night.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 143 PM CDT Thu Aug 21 2025

It has taken many hours to finally break down the stratus that
advected into our northeast CWA this morning, and as of 2 PM, it`s
finally transitioning to a cumulus field.  A large area of diurnal
cumulus has fired up over the CWA and surrounding region as well,
with cloud based of 3500-5000 ft.  While the air mass overhead is
much cooler than past days, we are seeing quite a bit of moisture
trapped under the inversion around 750mb.  Unfortunately, that
moisture will continue to bring issues to low level cloud cover,
fog, and forecast temperatures through Saturday morning when a cold
front finally pushes through from the northwest.

Tonight, with diurnal cumulus fading early, a mostly clear sky and
light winds will lead to at least patchy fog formation, with favored
locations seeing potentially dense fog in the sunrise +/- 2 hour
time frame. 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%.

Looking toward Friday, a pleasant late summer day is forecast, with
winds shifting towards the south/southwest during the day, and
cumulus a little less widespread.  Temperatures in the lower 80s
seem on target for this day in the "warm sector" ahead of the cold
front late Friday night.

Friday night, the main convective event which remains conditional,
should mainly impact areas well to our west and north, in the
Dakotas and western Iowa and MN. The late arriving cold front,
appears not to have much available LLJ interacting with it, nor
convergence.  The poor timing suggests surface instability will be
very limited, and any convection looks to be in a decayed state,
with potentially a nearly dry fropa in most places.  Pops remain 20-
40% in this period, but QPF is almost assured to be very light,
under 0.10".

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 143 PM CDT Thu Aug 21 2025

Windows open...Jackets suggested! (at night)

After Saturday, which remains mild in the 70s/lower 80s, the
complete transition to dry cool air will be in place Saturday night
through at least Wednesday.  Highs in the upper 60s to lower 70s,
and lows in the upper 40s to low 50s are forecast, with sunshine,
dry weather, and a nearly continuous northwest wind.  This early
Fall weather will certainly be the most significant cool intrusion
since the short stint in early August, when highs were in the upper
70s and lows in the upper 50s.

While expectations are for dry conditions at nearly all extended
forecast days, the cool air aloft may allow for some diurnally
driven cumulus and sprinkles/showers at times, and any embedded
short wave in this cyclonic flow could provide forcing for a brief
wetting rain in this pattern ahead.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 628 PM CDT Thu Aug 21 2025

High pressure will lead to beautiful weather through the period
with prevailing VFR. Patchy shallow fog is possible late tonight
into early Friday AM. Confidence is low on the development of
the fog and on its extent/severity; have MVFR visibilities in
the TAFs for now, with confidence too low to mention IFR/LIFR
with this update.

&&

.HYDROLOGY...
Issued at 143 PM CDT Thu Aug 21 2025

Routed water from upstream, is forecast to bring significant
rises to the Cedar River and Wapsipinicon in the coming days.
Levels may approach or exceed minor flood stage at
Conesville(Cedar), and near DeWitt(Wapsi). If forecasts remain
on track, and river flood watch may be issued tomorrow.

&&

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

&&

$$

SHORT TERM...Ervin
LONG TERM...Ervin
AVIATION...Uttech
HYDROLOGY...Ervin