814
FXUS63 KDVN 170816
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
316 AM CDT Thu Sep 17 2026

.KEY MESSAGES...

- A Flood Watch remains in effect for areas south of Highway 20
  through 10 AM this morning. Rainfall rates of 1-2 inches per
  hour at times will produce 1-3 inches of rain with localized
  areas of 3-5 inches possible (30-50%) north of I-80.

- A Dense Fog Advisory is in effect for the I-380 corridor and
  southeastern Iowa through 9 AM this morning. Visibility could
  drop to a quarter of a mile in some spots.

- The wet weather pattern will continue through the weekend with
  rounds of rain which may be heavy at times. There will be
  periods of dry weather between each round.

- The repeated rounds of rain will result in general rises on
  the Mississippi River with the potential for river flooding
  on tributary rivers. Refer to the hydrology section for more
  information.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 316 AM CDT Thu Sep 17 2026

After a stormy start to the day, conditions are expected to
improve by late morning after a mid-level trough passage.
Rainfall totals between 1-3 inches are expected north of I-80
with latest CAM guidance having a low-to-medium chance (30-50%)
of 3+ inches near and north of Highway 30. Dense fog also
impacting the eastern outlook area this morning is expected to
begin lifting between 8-9 AM. Northerly flow in the low- to-
mid- levels will put a damper on shower coverage (10-20%) this
afternoon compared to the last few days, and remnant cloud cover
from last night`s system should keep highs in the 70s areawide
outside areas south of Highway 34 that could reach the mid-80s.
Heading into tonight, winds are forecasted to shift back
easterly ahead of an approaching warm front in association with
surface cyclogenesis along the Front Range in Colorado. The WAA
wing north of this boundary will produce scattered storms
(50-70%) across eastern Iowa and northwest Illinois late tonight
into Friday morning. The short duration of this round should
limit the rain totals to less than inch (70-90% chance).

By Friday afternoon, the lobe of mid-level vorticity that
spawned the Colorado low moves into the Upper Mississippi River
Valley before being ejected eastward by the zonal flow. This
drags the low pressure center northeastward towards Iowa. As the
winds shift to out of the southeast, a warm, moist air is
pulled northward into the CWA, setting the stage for another
round of heavy rain north of I-80 Friday night into Saturday
morning. Latest ensemble guidance shows a swath of 0.25-0.75 of
an inch along the Highway 20 corridor (50-70% chance). The
coverage and intensity of these storms will decrease throughout
the day on Friday but remain scattered (40-60%) in nature along
the Highway 20 corridor as the low pressure center drifts into
northern Iowa.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Issued at 316 AM CDT Thu Sep 17 2026

Saturday night-Monday...A shortwave trough that has been
camping across the western CONUS for most of the week will
finally propagate eastward into the Northern Rockies Saturday
night. Shortwave ridging over the Mid-to-Upper Mississippi River
Valley introduces southwesterly flow aloft, pulling another
mid-level vorticity lobe northward into the north-central
Plains. This mid-level trough is forecasted to redevelop storms
(50-70% coverage) along a cold front moving through the area.
The SPC has a Marginal Risk, Level 1 out of 5, for most of the
outlook area for isolated damaging winds, but the latest LREF
guidance only has a 20-40% joint probability of SBCAPE exceeding
500 J/kg and the sfc-to-500 mb bulk shear exceeding 30 knots.
Therefore, any convection that forms should struggle to
organize.

After Saturday night, scattered PoPs (40-70%) will stick around
into Monday as weak shortwaves rotating around the main trough
axis, now over the Northern Plains, keeps CVA over the area. By
Monday though, most precipitation will be in the form of rain
showers as the boundary and low pressure over Missouri drifts
further south and northeasterly flow from a high pressure over
Ontario pumps in cooler air.

Tuesday-Wednesday...The shortwave trough over the Northern
Plains finally reaches the Midwest on Tuesday. Isolated cold-
core showers (20-30% coverage) could stick around during the day
before subsidence sets in on the backside of the trough heading
into Tuesday night and Wednesday. The persistent northeasterly
flow should allow for seasonable temperatures with highs only in
the mid-60s to low 70s (60-90% chance)!

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1251 AM CDT Thu Sep 17 2026

Our eastern CWA is currently plagued by an IFR-to-LIFR cloud
deck and fog that is impacting CID and DBQ and will eventually
trek eastward towards BRL and MLI over the next couple hours. In
addition to this deck, another bout of heavy showers and
thunderstorms is expected to develop along the I-80 corridor
over the next few hours and move to the east-northeast towards
CID, DBQ, and MLI. This will reinforce the IFR-to-LIFR ceilings
and visibilities through at least 14 UTC before ceilings slowly
rise throughout the day with VFR-to-MVFR conditions returning by
the afternoon at all sites. The winds over the next 24 hours
should remain light as they shift from easterly to
northeasterly, being variable at times.

&&

.HYDROLOGY...
Issued at 231 PM CDT Wed Sep 16 2026

With a wet pattern expected to remain in place through the
weekend and early next week, rising river levels are expected to
occur.

Right now current forecasts and extended ensemble forecasts
show within bank rises along the Mississippi with some areas
approaching flood stage (10-20%). Area tributary rivers will
also see rises. The Cedar, Iowa, Skunk and Wapsipinicon Rivers
have a 20-40% chance of reaching flood stage over the next 10
days. The Green, Rock and Pecatonica Rivers have a 10-20% chance
of reaching flood stage.

These probability are based on the current forecasted rainfall.
If the rainfall is heavier/lighter or in a different location
then the probabilities of the tributary rivers reaching flood
stage with either increase or decrease.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Dense Fog Advisory until 9 AM CDT this morning for IAZ040-041-
     051-052-063-064-076-077-087-088-098-099.
     Flood Watch until 10 AM CDT this morning for IAZ051>054-
     063>068-076>078-087>089-098-099.
IL...Flood Watch until 10 AM CDT this morning for ILZ007-009-
     015>018-024>026.
MO...Flood Watch until 10 AM CDT this morning for MOZ009-010.

&&

$$

SHORT TERM...Delaune
LONG TERM...Delaune
AVIATION...Delaune
HYDROLOGY...08