778
FXUS63 KDVN 092315
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
615 PM CDT Wed Jul 9 2025

.KEY MESSAGES...

- There is a daily risk of isolated to scattered showers and
  thunderstorms (20-30%) that will be most favorable in the
  afternoon and early evening. Thunderstorms Thursday night will
  have the potential to be stronger as a cold front moves into
  the area.

- There is a signal suggesting a risk of heavy rainfall late
  this week into the weekend. With rivers already running above
  normal for mid- summer, the risk of river flooding would
  increase if the heavy rainfall is realized.

- Seasonal temperatures and humidity levels will continue into
  week.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 303 PM CDT Wed Jul 9 2025

Diurnal convection is attempting to generate across the area this
afternoon. However, mid-level lapse rates are not good which is
helping to suppress convection in spite of being above the
convective temperature.

Regardless, a handful of diurnal cells should develop through sunset
but 95-98% of the area will remain dry.

Storms will develop in the Plains this afternoon and organize into a
thunderstorm complex that should move generally east southeast or
southeast through sunrise Thursday. The storm complex will be in a
decaying mode but areas west of the I-380/U.S. 218 corridor may see
an isolated shower or storm shortly after sunrise.

Winds will continue to remain light tonight which raises the
potential of patchy fog developing again east of the Mississippi.

Thursday will be interesting.

The decaying thunderstorm complex will move into eastern Iowa during
the morning producing isolated to scattered (20-40%) convection.
Boundaries left over from this convection will help provide a focus
for the diurnal convection that develops in the afternoon. Right now
scattered (30-40%) coverage of diurnal storms seems reasonable.
However, if the nocturnal storm complex develops an associated upper
level disturbance, then areal coverage of convection would be
higher.

Likewise, if there is a complex generated upper level disturbance,
then the potential for isolated severe storms would also increase.
Right now SPC has a marginal (level 1 out of 5) risk for severe
storms Thursday afternoon/night. The primary risk looks to be
damaging winds from precipitation loaded downdrafts, but, storm
scale interactions from outflow boundaries could result in a brief
spin-up tornado.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 303 PM CDT Wed Jul 9 2025

Thursday night through Saturday
Assessment...medium (40-60%) confidence on a daily risk of storms.
Potential for one or more heavy rain events and flooding is
increasing.

The end of the week time period will be interesting.

If there is a storm generated upper level disturbance, it will move
across the area Thursday night into Friday and potentially generate
some strong to severe storms. Damaging winds from precipitation
loaded downdrafts look to be the primary risk.

At the same time, tropical moisture will begin flowing north into
the area and establish a tropical connection with the Gulf on
Friday. Thus along with the severe risk there will also be a
developing heavy rainfall risk.

Areal coverage for rain Thursday night into Friday is 30-50% per the
model consensus. This coverage appears reasonable but there will
likely be pockets of 60-80% areal coverage.

Friday night into Saturday could be very interesting.

A seasonably strong low associated with a cold front will sweep
through the area. At the same time the tropical connection with the
Gulf intensifies. Model PWATs are forecast to be approaching 2
inches which would be at or above the 90th percentile of the DVN
sounding climatology. Thus there is signal pointing to the potential
for a period of very heavy rainfall Friday night into Saturday.

The location of the heaviest rainfall is not known as storm-scale
and other non-linear processes are not being handled well this far
out. Regardless, given a a signal pointing to the potential for
excessive rainfall, it bears watching over the next few days.

Saturday night through Wednesday
Assessment...medium (40-60%) confidence on a daily risk of storms.

Ongoing storms from Saturday will end as the front finishes moving
through the area. The potential exists for a vast majority of the
area remaining dry from late Saturday night through Sunday night.
Some weak upper level disturbances may potentially generate some
weak diurnal convection but 90% of the area looks to remain dry.

Monday through Tuesday the familiar theme of diurnally driven
convection will be seen. The model consensus supports this with 20-
30% coverage for afternoon/evening showers and storms across the
area.

Tuesday night into Wednesday the global models are forecasting yet
another front moving through the area. Residual moisture across the
area and forcing from the front will help generate more showers and
storms. The model consensus currently shows 30-50% coverage.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 612 PM CDT Wed Jul 9 2025

A few evening cumulus will quickly dissipate for a mostly clear
overnight with light winds. Slightly drier air should help keep
fog from being much of a problem tonight. A dissipating round of
showers and weak thunderstorms may approach eastern Iowa towards
the 12-15Z time frame, and is most likely to only impact the CID
terminal, with dissipation farther east. Thus, I`ve retained the
prob30 group for thunder at CID and kept the remaining TAFs dry
for now. A low chance around 20-30 percent generally exists in
all locations tomorrow afternoon.

&&

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

&&

$$

SHORT TERM...08
LONG TERM...08
AVIATION...Ervin