716
FXUS63 KDVN 171911
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
211 PM CDT Thu Sep 17 2026

.KEY MESSAGES...

- 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.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 200 PM CDT Thu Sep 17 2026

As of early this afternoon, a quasi-stationary front was draped
across eastern Iowa into northwest Illinois, approximately
along the I-80 to Highway 30 corridor. GOES visible imagery
showed widespread low clouds north of the front where
temperatures were in the upper 60s to mid 70s. Mainly clear
skies were noted south of the boundary and temperatures were
much warmer into the 80s (~upper 80s south of Highway 34),
accompanied by very humid conditions with dewpoints in the lower
to mid 70s. This hot and humid air mass has pushed heat indices
into the mid 90s to near 100 degrees across the far south.

Heading into tonight, winds will shift to the east-northeast in
response to surface cyclogenesis along the Front Range in
Colorado. A wave of warm air advection aloft may lead to
scattered showers and isolated storms (20-60%) late tonight into
Friday morning, working west to east through portions of the
area. Highest chances for some measurable rain are to the west
and northwest of the Quad Cities. This activity looks to move
through relatively quickly, thereby limiting total rainfall
amounts with much of the area receiving under 0.25". A few
isolated showers and storms remain possible through Friday
afternoon, but with most of the area likely to stay dry during
this period.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 200 PM CDT Thu Sep 17 2026

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 Saturday but
remain scattered north of I-80 as the low pressure center
drifts into northern Iowa.

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 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 seasonably cool temperatures with highs only in the
lower to upper 60s!

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1250 PM CDT Thu Sep 17 2026

A warm and humid air mass will remain over the area into Friday,
and with light winds resulting in little boundary layer mixing,
periods of MVFR/IFR ceilings are likely. Scattered showers and
isolated storms are possible Friday AM with low confidence on
coverage this far out (20-40%). Patchy fog may develop tonight
which could lead to periods of MVFR/IFR visibilities; however,
confidence is very low on the extent and severity.

&&

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

&&

$$

SHORT TERM...Uttech
LONG TERM...Delaune/ZU
AVIATION...Uttech