083
FXUS63 KDVN 172334
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
634 PM CDT Sun Aug 17 2025

.KEY MESSAGES...

- Scattered, slow-moving soaking storms will continue through
  mid-evening over parts of the area, mainly along the general
  I-80 corridor and north; heavy rainfall that may result in
  very localized flooding and brief funnel clouds with these.

- Hot and humid conditions will continue across the area on
  Monday. Heat headlines for Monday will be dependent upon where
  boundaries produced by the previous night`s convection are
  located. Slightly less humid conditions are expected on
  Tuesday.

- Periodic chances (20-40%) of storms will continue through
  Tuesday with strong to severe storms possible. The better
  chances for rain look to be centered around Tuesday when a
  cold front moves through the area.

&&

.UPDATE...
Issued at 630 PM CDT Sun Aug 17 2025

Slow-moving storms will continued into mid-evening, mainly along
and north of the general I-80 corridor. High values of mlCAPE
(>3000 J/kg), including in the lowest levels (0-3 km CAPE of
>175 J/kg), will help to support these storms in an otherwise
marginal deep layer shear environment. With multiple boundaries
including a webbing of outflow boundaries north of the Quad
Cities, some of these storms have exhibited stretching updrafts
and supercell characteristics in the low-levels, with
temporary rotation noted. That means the potential for funnel
clouds and and can`t rule out completely a brief tornado.

Of possibly more note, is locally heavy rainfall with the
sluggish storm motions and precipitable waters above 1.7
inches. This includes where there are greater coverage of
storms, namely near the U.S. Highway 20 corridor in Iowa, and in
parts of Bureau and northern Putnam Counties in Illinois,
through 8-9 P.M.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 300 PM CDT Sun Aug 17 2025

As expected the remnant outflow boundaries from the nocturnal
convection combined with diurnal heating and elevated theta e
gradients to generate isolated convection. Some further development
is expected through sunset but overall coverage will be isolated to
low end scattered (10-35%). Said convection will dissipate shortly
after sunset. Brief downpours are likely where it does rain.

After midnight weak warm air advection will start moving east from
central Iowa. This additional moisture combined with weak forcing
should be enough to initiate isolate to low scattered (20-30%)
nocturnal convection. However, the better low level jet (albeit
weak) remains in central Iowa so the convection in eastern Iowa may
end up being more isolated in nature.

Monday will be interesting. Another heat advisory will be needed but
the areal coverage will be dependent upon where nocturnal convection
is located along with any associated outflow boundaries. An educated
guess on areal coverage is along and south of I-80.

Nocturnal convection arriving from the west will decay during the
morning as the forcing becomes weaker. There may or may not be
isolated convection that persists into the afternoon before the
diurnal cycle of convection begins. Overall coverage during the
afternoon still looks to be isolated to low end scattered (15-30%).
A few strong to severe storms cannot be ruled out.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 300 PM CDT Sun Aug 17 2025

Monday night through Tuesday night
Assessment...Medium (30-50%) confidence regarding rain chances

Monday night into Tuesday the much anticipated cold front from the
coming pattern change will move through the area. The models vary on
the overall timing but the late Monday night/Tuesday morning time
frame seems to be favored.

Convection that develops Monday afternoon will continue into Monday
evening before decaying and possibly dissipating. Any convection
that remains potentially will get a new life as the cold front
arrives. Overall coverage of convection looks to be scattered (25-
50%) Monday night with coverage decreasing on Tuesday.

Some solutions push the front through the area and leave Tuesday
night dry while other solutions slow down the front and potentially
stall it briefly along the IA/MO border into central Illinois. As a
result, the model consensus keeps 20-30% pops going south of I-80
Tuesday afternoon with lingering rain south of an Ottumwa, IA to
Galesburg, Il line Tuesday evening.

Tuesday will still be very warm and humid across the area with peak
afternoon heat indices of 95 to 100 for areas south of Highway 30.

Wednesday through Sunday
Assessment...very high (>90%) of cooler temperatures. Low (10-20%)
confidence regarding rain chances

As mentioned yesterday the heat dome will retrograde to the Rockies
and potentially the Intermountain Region. This retrogression will
bring zonal to west northwest flow aloft and temperatures around or
slightly below normal.

Given the flow pattern aloft, mainly dry conditions will be seen
during the period. However, I cannot rule out rogue diurnal
convection occurring in the afternoon/evening. There is a weak upper
level disturbance progged by the models to move through Friday night
which `may` result in a slightly better chance of some isolated
convection occurring. Regardless, 95 percent of the area will remain
dry the second half of the week and next weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 630 PM CDT Sun Aug 17 2025

Scattered storms will be very slow moving through mid-evening.
Confidence is high that some of these will be at least within
15 miles of DBQ, CID, and MLI, but whether or not they impact
the airfields directly is on the lower end. If they do, locally
heavy rainfall taking visibility into the IFR category can be
expected. For overnight, in the wake of this activity, there may
be patchy shallow fog, though enough wind where it should not
result in a big problem. Given the saturated low-levels, some
model guidance does result in IFR ceilings at DBQ. Not enough
confidence yet for this but have hinted at it.

For thunderstorm potential on Monday, there are initial signs
that there are two windows, with semi-organized but weakening
storms moving eastward into eastern Iowa during the morning, and
redeveloping storm in the afternoon.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Heat Advisory until 8 PM CDT this evening for IAZ051-052-
     063>065-067-068-076>078-087>089-098-099.
IL...Heat Advisory until 8 PM CDT this evening for ILZ015>018-
     024>026-034-035.
MO...Heat Advisory until 8 PM CDT this evening for MOZ009-010.

&&

$$

UPDATE...Friedlein
SHORT TERM...08
LONG TERM...08
AVIATION...Friedlein