735
FXUS63 KDVN 180224
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
924 PM CDT Fri Oct 17 2025

.KEY MESSAGES...

- Fog, some dense, is possible late tonight and Saturday morning
  across parts of eastern Iowa, mainly along and northwest of a
  line from Iowa City to Dubuque.

- Periodic chances for showers and thunderstorms from late this
  evening through Sunday morning.

- Heaviest rainfall will fall east of the area, with Illinois
  counties seeing totals half an inch up to one inch of rain.

- Seasonable mid to late October weather is forecast for much
  of next week with no significant precipitation expected.

&&

.UPDATE...
Issued at 915 PM CDT Fri Oct 17 2025

Some of the latest Hi-Res guidance continues to increase the
signal for fog very late tonight and Saturday morning across
north/west portions of the service area. This seems
reasonable, particularly along/NW of an Iowa City to Dubuque
line which is where the guidance favors the best overlap
or juxtaposition of light winds, added low level moisture
aided by ongoing showers, and partial clearing / residence near
the back edge of cloud cover. The fog could be dense in
pockets. We`ve updated to add mention in the forecast for these
areas and also added mention in the Hazardous Weather Outlook.

Otherwise, band(s) of showers will continue to shift east across
the area the rest of tonight (at least likely coverage 60%+).
Scattered storms are possible as well particularly late this
evening and overnight near to south of I-80 with a ramping LLJ
and elevated instability. Can`t rule out some small hail with
the stronger cores.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 243 PM CDT Fri Oct 17 2025

Complex upper level pattern a series of waves approach the area
in the short term. The first one moves through the area today
dragging a cold front across Iowa. This front will stall up as
another stronger shortwave moves NE into the area while a deeper
wave to our NW moves in. These two waves phase over the area
around 00z Sunday, leading to intense height falls and
subsequent rising motion. The majority of this will occur
outside of the short term period. The first wave will be
discussed below.

Overall forcing for the first wave is weak. Currently to our
west, good returns are seen on radar corresponding to a sfc
boundary with this wave. This boundary is expected to become
more diffuse as the wave moves east. The main forcing for ascent
will become the wave resulting scattered showers and even a
rumble of thunder tonight into the AM. Low-level moisture is
forecast to be low and thus likely impeding to actually rainfall
until early morning across the area. The best chance for rain
will be likely around 12z and after and along and east of the
Mississippi River. The storms tonight could have some small hail
with them, but severe weather is not expected.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 243 PM CDT Fri Oct 17 2025

Turning to Saturday evening into Sunday morning. Strong
dynamics, a sign of the change in seasons, overspreads the area.
140 to 150 meter 12 hour height falls at H5 will lead to
intense vertical motion. The height falls will move east the
area by 18z on Sunday. Looking to moisture, latest GFS has
slowed down on the front leaving the area. The deep moisture
looks to hang up along the Mississippi River in the afternoon
before moving east by 06z. This will give us a good 6 hour
window of deep moisture and ascent. CAMs are trending towards
convection, probably switching to largescale stratiform rain as
the front moves east.

Again, looking at the cold front being slower as cyclogensis
takes hold over our area during the evening on Sunday, there
remains a window where deep layer shear, and instability
overlap. CAMs are starting to show better chances for more
convection, especially along and east of the Mississippi River.
Looking at soundings, there is very good directional shear in
the llvls with not much speed shear. At the top of the profile
there is good speed shear. There is also around 140-160 J/kg of
0-3 CAPE. This means that ingredients are in place for updraft
organization. I still think we will be watching convection
during this time and would bet against severe weather, but can`t
rule it out.

Another deep upper trough is forecast to dig into the Midwest
and Great Lakes early next week with an attendant surface low
tracking north of the local area across the Great Lakes. After a
brief warm up ahead of the trough on Monday, cooler more
seasonable temperatures are expected for the rest of the week.
We`ll stay on the drier southwest flank of the early week
system, so rain chances will be on the low side for Monday
night into Tuesday. High pressure then returns for mid to late
in the week. We`ll have to watch for frost potential along/north
of Highway 30 Tuesday night, which will depend on how quickly a
surface ridge builds in behind the departing low. Latest NBM
has mid 30s for lows north of I-80, but again confidence is low
this far out.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 715 PM CDT Fri Oct 17 2025

Cold front through central Iowa is expected to shift east while
undergoing frontolysis /weakening/ with an eventual subtle
surface wind shift/trough stalling across the region overnight
into Saturday. Prior to doing so it will bring a chance of
showers (40-60+%) across the terminals mainly in the 02z-12z
timeframe from west to east, with the shower potential
residing for a few hours at any one terminal during this
timeframe. There is a chance for thunder, but confidence
is too low for inclusion at this time although will continue
to monitor trends and amend to include if needed. Conditions
in the showers look to be largely VFR CIGs and VFR to MVFR
visibilities. Any storms would bring the potential for brief
lower conditions (IFR to lower MVFR), mainly for visibility.
LLWS was added to KMLI and KBRL during the first 6-9 hours of
the TAF, as winds this evening into the overnight (04z-08z)
look to increase to around 40 kt from the SW in the 1-2kft agl
layer while at the surface remain more southerly around 10 kt
with some sporadic higher gusts possible.

Late tonight into Sat AM (09z-14z) there is an increasing signal
for fog potential. At this time, the greater potential looks
to be just north/west of the KCID and KDBQ terminals with
recent wet ground and a decreasing wind. NBM and HREF
probabilities for less than 5 mile visibility are roughly around
20 percent at both sites. However, the HREF shows pockets of
modest probabilities of 30-50% for less than 5 mile visibility
just northwest of KCID and KDBQ terminals, and the 15z SREF
is at 30-50% for less than 3 mile visibility. This is where
some of the latest CAM/HI-Res guidance is more aggressive with
fog per surface visibility plots and would support potentially
even dense in pockets with LIFR/VLIFR visibilities. For now,
I`ve opted to add MVFR fog at KCID and KDBQ, but will have to
watch the obs/guidance trends closely for the potential of
needing to lower conditions in fog at these sites.

Late in the TAF period and especially just beyond, a stronger
cold front is expected to push across the terminals accompanied
by increasing shower chances and a shift to gusty WNW winds.

&&

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

&&

$$

UPDATE...McClure
SHORT TERM...Gibbs
LONG TERM...Gibbs
AVIATION...McClure