643
FXUS63 KDVN 201127
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
624 AM CDT Sun Jul 20 2025

.KEY MESSAGES...

- Flash Flood Watch in effect through 1 PM today as showers and
  storms move into the area this morning.

- Daily storm chances through the coming week will bring chances
  for strong to severe storms and flash flooding.

- Temperatures increase after Monday with highs in the 90s for
  most of the week.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 228 AM CDT Sun Jul 20 2025

GOES satellite imagery this morning shows a swath of convection
across west-central to southern Iowa with IR satellite
especially vibrant with a line of towering storms. Heavy rain
and frequent lightning are being observed within this line with
progression expected towards the southeast within the latest CAM
guidance. The Flood Watch active until 1pm this afternoon favors
the southern 3/4ths of the CWA as this line will likely be the
primary driver behind any flooding potential, especially if the
linear shape continues as it moves through which would result in
prolonged periods of heavy rain from training thunderstorms. Per
the SPC Mesoanalysis, PWAT values remain above 2.0 in southern
to southeastern Iowa and northeastern Missouri with the most
efficient moisture transport also favoring this region. The
`tropical` airmass and nocturnal timing have largely kept severe
weather from occurring tonight as heavy rain and lightning will
remain the primary outcomes of the storms as they continue this
morning.

After this line of storms pushes through the region by late
morning to early afternoon, overall area rain chances dwindle
with sprinkles possible underneath a continuous deck of
stratocumulus clouds which look to persist through the afternoon
and evening. A few models try producing another round of storms
favoring northern Missouri by the late evening with forecast
soundings showing a healthy 2000+ J/KG MLCAPE alongside 30-35kts
of deep layer shear and a favorable hodograph as a warm front
moves northwards from west-central Missouri. This boundary will
be the key thing to monitor within guidance throughout the day
as it will serve as the locus for severe weather potential, with
additional warm core rain possible north of the boundary as
well.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 228 AM CDT Sun Jul 20 2025

The longer term period will be marked by a warmup starting
Tuesday and lasting through the remainder of the week, with high
temperatures in the low 90s likely beginning Wednesday and
continuing towards the weekend. In addition, diurnal shower and
storm chances will be present with weak ridging present to the
north amidst weak zonal flow above 500mb as the lower level
winds will advect warm and moisture rich air into the region
beginning Tuesday and lasting throughout the week, alluding the
previously mentioned Ring of Fire pattern. Ensemble guidance
shows sporadic QPF across the entire period with the GEFS
showing the sole mostly dry period being Thursday, as shower and
storm chances show up frequently amidst the membership
otherwise. In terms of heavier rain, aside from a direct hit
from a storm it appears that the best chance will be later in
the week favoring next weekend with a more powerful upper level
shortwave appearing within the deterministic global guidance.
Until there is a better handle on the synoptic forcing, the
timing and intensity will change throughout the week until we
get a bit closer.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 624 AM CDT Sun Jul 20 2025

Fairly solid rain shield continues this morning just south of DBQ,
impacting the remainder of the WFO DVN TAF sites. That said, DBQ may
well catch some of the fringes of the precip this morning.
Conditions are generally VFR with the precipitation, though a few
brief periods of MVFR cannot be ruled out. Certainly cannot rule out
a few bouts of CB/TS at any given site. As the precipitation slowly
wanes going into the afternoon, MVFR ceilings are likely to stick
for much of the afternoon hours prior to improving to VFR this
evening, though ceilings will remain in place throughout this
duration. There is some concern that BRL may see a period of pre-
dawn IFR ceilings Monday morning, mainly due to plentiful moisture
(due to today`s rain) being caught under the nightly inversion as
winds drop off. Winds will generally come from the E in the 5-10kt
range throughout this duration.

&&

.HYDROLOGY...
Issued at 1053 AM CDT Sat Jul 19 2025

What has changed...

A flood warning has been issued for the Iowa River at Marengo,
IA.

A flood watch has been issued for the North Skunk River near
Sigourney, IA.

Discussion...

Overnight bands of 1 to 3 inches of rain fell across parts of
eastern Iowa and west central Illinois. Within those bands were
localized pockets of 3+ inches.

Another round of heavy rainfall is expected tonight into Sunday
morning. This round of rain is concerning as the Weather
Prediction Center has much of the area outlooked in an upper end
slight risk for excessive rainfall. The risk of excessive
rainfall will continue into Monday night.

As mentioned yesterday atmospheric moisture levels will be
near 2 inches tonight which is greater than the 90th percentile
for July. With a tropical moisture connection developing with
the Gulf, warm rain processes have a high probability of
dominating which will lead to very efficient rainfall production.
There is a high probability of rainfall rates of 1 to 2+ inches
per hour.

Data so far this morning from weather models is pointing to the
general area of along or south of I-80 as being the focus for
the heavy rainfall tonight into Sunday morning. There will
likely be more bands of 1 to 3 inches of rain with locally
higher amounts. If storms repeat over the same areas (there is a
50-60% probability of this occurring) then rainfall rates of 2+
inches per hour would lead to rapid runoff and resultant flash
flooding. This additional round of heavy rainfall will produce
general rises on area rivers with the potential for river
flooding.

The following tributary rivers will need to be watched carefully
through the end of July since they already have above to much
above normal streamflows; Cedar, English, Iowa, North Skunk,
Skunk and Wapsipinicon.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flood Watch until 1 PM CDT this afternoon for IAZ051>053-
     063>068-076>078-087>089-098-099.
IL...Flood Watch until 1 PM CDT this afternoon for ILZ015-016-
     024>026-034-035.
MO...Flood Watch until 1 PM CDT this afternoon for MOZ009-010.

&&

$$

SHORT TERM...NWS
LONG TERM...NWS
AVIATION...NWS
HYDROLOGY...08