784
FXUS63 KDVN 090234
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
934 PM CDT Fri Aug 8 2025

...Updated for 00z Aviation...

.KEY MESSAGES...

- Active weather is expected to affect our region through the
beginning of next week as storms are expected staring Saturday
morning lasting through Monday.

- Heavy rain, a moderate risk of excessive rainfall, flash flooding
and severe weather is possible starting Saturday through Monday
morning.

-Widespread 3 to 5 inches of rain are possible through Monday
morning with some areas receiving higher amounts.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 313 PM CDT Fri Aug 8 2025

Potent setup taking shape this weekend as a synoptic boundary is
expected to stall across the area.  LLJ is expected to ramp up
across the area tonight and again Saturday night into Sunday.  While
the strength of this LLJ diminishes during the day, continued
moisture convergence suggests at least some continual convection
during the day.  This forcing, tied with PWATs over 2.2 inches and
an unstable airmass will result in very efficient heavy rain
producing storms.  With weak impulses moving through the flow, a
typical heavy rain/flash flood setup is taking shape.  This setup
will last into at least Monday morning as another set of active
overnight storm coverage is expected Sunday into Monday morning.

Also, we look at like we have the potential for severe storms on
Saturday as strong instability >4000 J/kg SBCAPE along with deep
layer shear of 30-45 knots will combine to support updrafts that
could produce damaging winds.  0-3km shear is sufficient to lead to
a cold pool/shear balance and bowing like features.  CAMs have these
storms bow out quickly, suggesting the window for severe winds from
any one storm is limited.   Sunday we are in a marginal risk for
severe weather again. Damaging winds are the main threat with this
risk, but it is highly dependent on what happens tomorrow night.

Rainfall and Flash Flooding

WPC has a moderate risk for excessive rainfall for day 2 and day 3
across our area.  A WPC moderate risk is usually a slam dunk for
flash flooding in that area, and not just one or two occurrences but
more likely multiple flash flood areas.  As such, we have issued a
flood watch for the area.  WPC`s forecast aside, guidance the PWATs
are in the ~99th percentile for this time of year.  This combined
with freezing levels in storms to near 16kft is conducive for
effective warm rain processes and very heavy rainfall.  Looking at
QPF amounts, HREF mean one hour QPF rates max out near 1 inch
Saturday night into Sunday.  Bumping this up to max values, some
guidance is predicting 2 to 3 inches of rain in an hour.  This does
not seem out of the ballpark, especially with the synoptic setup.
WPC 72 rainfall totals of 5 to 7 inches and bullseye of 9 inches in
SE Iowa tend to be on the higher end of guidance, where the NBM is
widespread 3 to 5 inches.  Nonetheless, I would not be surprised to
see isolated amounts near 10 inches by midday Monday.  The bulk of
the precip looks to fall Saturday evening into the overnight with a
less intense round Sunday night into Monday.

CAM Guidance:

The majority of guidance has most of our precip starting in the
afternoon to evening on Saturday.  Higher confidence in this period
being our most active remains.  The NAMnest, continues to show that
convection north of us dives south into the area tomorrow morning.
These storms would have a severe wind threat and heavy rain threat
as well.  This may even set the case for more impactful flash
flooding for later during the period on Saturday night.  This is the
outlier, but has been consistent, so can`t rule this out as a
potential.

Heat on Saturday:

The setup for hot temperatures remains on Saturday, especially if we
don`t get storms in the morning.  As such, decided to hold off on a
heat advisory at this time.  Mid shift will have a better idea on
convective coverage and thus the potential need for a heat advisory.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 330 AM CDT Fri Aug 8 2025

Bouts of heavy rainfall may continue into Sunday, although
confidence on the placement of the surface boundary is low due
to its dependence on how the Saturday night convection evolves.
Heading into next week, we`ll continue to see shortwaves passing
through the area near- daily. Thus, we are looking at the
potential for daily chances of precipitation over much of the
area through at least Tuesday. At this time, it doesn`t seem to
be a complete washout through that timeframe. Rather, there
should be plenty of dry time between passing systems. With this
pattern in place, we will remain warm and humid through the
first half of next week. Too soon to determine any severe threat
with these passing waves.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 925 PM CDT Fri Aug 8 2025

Predominantly VFR conditions for much of the period, with the
potential for convection and attendant MVFR/IFR conditions
Saturday.

Satellite shows some wildfire smoke across the region. Obs and
latest HRRR near surface smoke forecasts suggest most if not all
of this is aloft and will remain so with little in the way of
impacts to visibility. Winds will be gusty at times tonight into
Saturday at around 10 to 20+ kts.

The main challenge will be the timing of precipitation chances
into the terminals. Latest observational data supports continued
storm development across parts of MN ahead of a cold front and
in an area of weaker capping, with the potential for upscale
growth into a line or clusters. Should this occur then the
potential exists for propagation to the south possibly reaching
into parts of eastern Iowa and northwest Illinois around 12z
through 17z while slowly decaying. Confidence is not particularly
high as CAM guidance varies on the extent of any upscale growth.
Even if this does not occur do think there would still be some
potential for at least scattered convection with a veered LLJ
and attendant warm/moist advection to warrant at least PROB30
mention for tomorrow AM, particularly at DBQ and CID. Additional
redevelopment would be possible later Saturday afternoon.

&&

.HYDROLOGY...
Issued at 313 PM CDT Fri Aug 8 2025

Rises on area rivers are expected through the weekend and into next
week.  NCRFC is using 24 hours of QPF in their forecasts.  While
this may not capture the majority of the rainfall we expect to see,
low confidence on QPF past 24 hours makes forecasts longer than that
subject to wild swings.  That said, we expect some rivers in flood
to start rising again and possibly to higher crests.  Additional
rivers may enter flood stage as well.  With the corn tasseled out, we
expect to see maybe more runoff than we have in the last few weeks
as the crops are storing less water now.  Stay tuned to additional
forecasts into the weekend.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flood Watch from Saturday afternoon through Monday afternoon
     for IAZ040>042-051>054-063>068-076>078-087>089-098-099.
IL...Flood Watch from Saturday afternoon through Monday afternoon
     for ILZ001-002-007-009-015-016-024>026-034.
MO...Flood Watch from Saturday afternoon through Monday afternoon
     for MOZ009-010.

&&

$$

SHORT TERM...Gibbs
LONG TERM...Gunkel
AVIATION...McClure
HYDROLOGY...Gibbs