686
FXUS63 KDVN 130954
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
454 AM CDT Mon May 13 2024

.KEY MESSAGES...

- Periods of showers and storms are likely today into tonight
  with the heaviest rainfall amounts south of Interstate 80.

- WPC has a Slight Risk for flash flooding for areas roughly
  along and south of I-80 due to the potential for slow moving
  showers and thunderstorms this afternoon into early tonight.

- Active weather will continue through the rest of the week with
  occasional chances for showers and thunderstorms.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 300 AM CDT Mon May 13 2024

Today

SPC mesoanalysis showed split upper level flow across the U.S.
and a partially cut-off upper low over the Southern Plains
associated with an active subtropical jet. This system will
slowly track toward the ENE across the Lower to Mid Mississippi
Valley, reaching far enough north to bring rain to portions of
eastern Iowa and northwest Illinois today. Deep layer WV
transport downstream of the mid level cyclonic circulation will
lead to a fairly moist atmosphere locally with PWATs peaking
between 1.30" - 1.50" by this afternoon and evening. Despite
being on the northern side of this system, given the relatively
high sun angle this time of year temperatures will manage to
reach the upper 60s in the west to mid/upper 70s in the east.
The warm air combined with an increasingly humid air mass with
dewpoints near 60F will yield surface-based CAPE near 1000 J/kg
by the afternoon per latest HREF.

As large scale ascent increases downstream of the 500mb vorticity
max and in a zone of elevated warm air advection, showers and
thunderstorms will quickly develop and increase in coverage from
S to N. WPC has a Slight Risk for flash flooding, roughly for
counties along and south of I-80. The areal coverage of showers
and storms and total rainfall amounts will drop off quickly to
the north of I-80.

The main concern today with the strongest cells is locally heavy
rainfall rates that could result in minor flooding or even
flash flooding. This is because as the 850mb low passes across
NE Missouri into southern Illinois, a pivoting deformation band
of slow moving showers and storms will likely set up across the
forecast area. Some of these cells could become nearly stationary
at times, leading to hourly rainfall rates of 0.50-1"+. The
heaviest rain amounts are anticipated in the counties south of
I-80 where a general 0.50" to 1.50" is forecast. However, as
mentioned locally higher amounts are likely. The HREF LPMM is
showing pockets of 2-4", which is a signal for what`s possible
on an isolated basis today. Will hold off on a Flood Watch for
now due to the expected localized nature of the heavy rain.

Tuesday

Shower chances will continue through the morning for most of the
area and across the south into the early afternoon. Breezy NE
winds will continue through the afternoon with highs only
reaching the mid 60s to lower 70s. Smoke aloft from Canadian
wildfires may overspread eastern Iowa and northwest Illinois
through the day, which could lead to hazy skies for the
afternoon and evening.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 300 AM CDT Mon May 13 2024

Wednesday - Friday: Surface high pressure is forecast to build
in later Tuesday into Wednesday, leading to a break in the wet
weather. The next system to impact the region arrives by late
Wednesday into Thursday, bringing another round of widespread
rain to the outlook area. Deterministic models have trended
toward a more progressive system, quickly shifting it to our
east by Thursday night. Another wave could bring scattered
showers and storms to the region on Friday (20-40%). Forecast
temperatures late in the week are near to slightly above normal.

Saturday - Sunday: An upper level ridge is forecast to build
into the Upper Mississippi Valley and Great Lakes with
1000-500mb thicknesses rising to near 570 dam. The NBM has low
chances (20-30%) for rain and max temps reaching the 80s.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 437 AM CDT Mon May 13 2024

Coverage of showers and storms is forecast to increase later
this morning into the afternoon/evening which will likely lead
to periods of MVFR ceilings and visibilities. The atmosphere
will become more humid today, increasing the potential for
heavy downpours and brief IFR conditions. The best chances for
heavier showers and storms are to the south of DBQ. Showers
will continue through the overnight as ceilings gradually
deteriorate to IFR across eastern Iowa and northwest Illinois.

&&

.HYDROLOGY...
Issued at 946 PM CDT Sun May 12 2024

New forecast by the River Forecast Center this evening showed
little to no change for the Wapsipinicon River near DeWitt. The
river should reach flood stage before 7am tomorrow morning and
slowly rise to 11.4 feet over the next 3 days. Depending on
where additional rainfall on Monday falls, more rises may be
possible. However, at this time the highest totals are expected
south of the Wapsi basin. The flood warning was continued with
this forecast issuance.

The forecasts for the Cedar and Iowa Rivers have come in lower
this evening. The Iowa River at Marengo now is expected to not
reach flood stage and as a result, I have cancelled the watch
here. The Cedar River near Conesville forecast was kept just at
flood stage for now due to the incoming QPF uncertainty. For
this reason, have kept the flood watch going there.

Taking a deeper dive into the QPF, widespread rainfall in the
0.5" to 1" range is expected in the next 24 hours, with some
localized higher amounts. The 12z HREF probability-matched mean
QPF values through Tuesday morning are painting a swath of
rainfall in excess of one inch, with some isolated amounts over
two inches slightly northward closer to the downstream portions
of the Iowa and Cedar River basins. This QPF placement and how
much runoff occurs will be very important to whether additional
rises are seen and if warnings will be needed.

&&

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

&&

$$

SHORT TERM...Uttech
LONG TERM...Uttech
AVIATION...Uttech
HYDROLOGY...Gross