234
FXUS63 KDVN 101040
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
540 AM CDT Wed Jul 10 2024

.KEY MESSAGES...

- There is a chance (40-60%) of scattered showers and
  thunderstorms this afternoon/evening. An isolated severe storm
  or two will be possible with heavy downpours, gusty winds, and
  funnel clouds the main threats.

- Increasingly humid Friday and into next week. Heat indices
  well into the 90s and even low 100s are forecast Sunday and
  Monday.

- Moderate to major river flooding continues on the Mississippi
  River with most sites crested or cresting in the coming days.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 320 AM CDT Wed Jul 10 2024

MSAS surface analysis and water vapor imagery early this morning
show the surface low that was previously tropical depression
Beyrl was centered over north central IN. Radar mosaics depict
the back edge of the showers finally just to our east. Very weak
flow aloft (under 15 kts up to 600mb) and some dry mid levels
were seen on our 00z DVN sounding. In contrast just to our
south on the 00z ILX sounding showed 30kts of mid level flow and
a nearly saturated profile with 1.82" precipitable water!

A mild start to the day is expected with temperatures and
dewpoints in the mid to upper 60s with clearing skies. Attention
then turns to the shortwave diving south out of MN into IA. This
wave is currently supporting showers/storms in western MN and
eastern SD.

This Afternoon/Evening...with a mild start and high sun angle
expect instability to build as we warm up today. Forecast
soundings and spatial progs show CAPE values in the 1200-1900
J/Kg range with PWs in the 1.3-1.5" range. The limiting factor
for organized severe weather remains meager deep layer and low
level shear. However, the diving shortwave may be able to
augment the kinematics enough that a few severe storms may still
be possible. Main threats would be marginally severe wind and
heavy downpours in the strongest cells. The 00z HREF 75th
percentile 1-hr QPF field has rainfall rates over 0.75"/hr in
the strongest storms and with slow movement, I wouldn`t rule
out a quick 1 inch of rain. In addition, the RAP13 NST progs up
to 1.5 and with a very subtle weak boundary across the area may
allow for funnel clouds this afternoon/evening. Something later
shifts will have to monitor. Regarding timing, the CAM consensus
and hi-res ensemble data would see convection develop around
18-19z and last until the 23-00z time frame.

Tonight...any storms will quickly dissipate after sunset and
loss of heating. Any clearing of clouds may allow for some fog
to develop in the weak low level convergent flow, but have left
out of the forecast for now. Overnight low temperatures, will
only drop into the low to mid 60s.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 320 AM CDT Wed Jul 10 2024

Thursday...an elevated boundary may allow for some lingering
showers to develop in northeast MO, southeast IA, and west
central IL early AM. Otherwise, subsidence behind departing
shortwave will bring dry conditions for the rest of the day for
most. Some models are still hinting at some diurnal
showers/storms, but feel this activity may remain just to our
south and east.

Friday-Saturday...return flow develops as high pressure slides
to our east. Model 1000-500mb RH progs suggest that most of the
area will be dry Friday even though it will feel quite humid
outside. Another wave will top the western ridge and move into
the northern Great Plains Saturday. Have maintained low slight
chance/chance PoPs Saturday for diurnally driven storms. Highs
Friday and Saturday will be in the mid to upper 80s.

Sunday-Monday...building western ridge will advect warmer 850mb
temps into the region with 850mb temps rising into the 23-26C
range. This will boost temps into the 90s and combined with
dewpoints in the low 70s (perhaps even higher due to mature corn
crop), will push afternoon heat indices into the upper 90s and
low 100s. Taking a look at the 00z ensemble data, the
probability of 100 degree heat indices or greater has increased
into the 50-70% range south of I-80 on Monday. This may require
a heat headline if trends continue. The failure mode to this
occurring would be convective debris clouds from a southward
propagating MCS into our area. It is indeed the time of year for
MCS tracks to ruin the forecast temps and subsequent humidity.
Something also interesting to note is the CSU machine learning
severe weather probabilities are highlighting much of the upper
Midwest for a risk of severe weather Sunday and Monday. This
will be something to monitor in later forecasts.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 539 AM CDT Wed Jul 10 2024

Scattered showers and isolated thunderstorms are expected this
afternoon and evening as a shortwave drops south into Iowa.
Confidence is high enough to include VCTS wording at CID/DBQ
with this issuance. VFR conditions are forecast, however some
brief MVFR/IFR vsbys may occur if a storm goes right over a
terminal. Later updates may need to include lower vsbys if
confidence increases on a direct impact. After this wave passes,
winds go calm and if clouds clear there may be some MVFR fog
that could occur. Confidence is too low to include mention at
this time.


&&

.HYDROLOGY...
Issued at 124 PM CDT Mon Jul 8 2024

Precipitation in the next few days, especially in Iowa, is expected
to be dry or very light. Thus, routed flow will continue on all of
our rivers.

The Mississippi River is currently cresting at major levels upstream
of Camanche, IA, and near crest through Illinois City.  The crest
may take 1 to as much as 3 days to pass. From Le Claire to
Burlington, the respective crests will commence within the next 1 to
2 days.

Keokuk is now forecast to crest within Moderate Flood category
beginning Friday.  Gregory Landing is forecast to remain near 19.5
feet through the week.

Tributary Rivers:


The Cedar River at Cedar Rapids crested below flood stage and will
fall over the next several days.

On the Cedar River at Conesville, minor flooding will continue. It
will see a secondary crest near 14.4 feet Wednesday night into
Thursday.

The Wapsipinicon River at Dewitt is forecast to remain in
moderate flooding category through late on Friday.

The Iowa River at Oakville is seeing high water levels due to
backwater affects from the Mississippi River. It is forecast to
remain near 11.4 or 11.5 feet through midweek and then rise to near
12.1 feet late Thursday into Friday.

&&

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

&&

$$

SHORT TERM...Gross
LONG TERM...Gross
AVIATION...Gross
HYDROLOGY...Gunkel