017
FXUS63 KDVN 131924
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
224 PM CDT Mon May 13 2024

.KEY MESSAGES...

- Periods of showers and storms continue this afternoon into tonight,
  with the heaviest rainfall amounts expected along and south
  of Interstate 80

- Showers will eventually come to an end Tuesday afternoon

- Periodic chances of showers and storms are in the forecast for
  Wednesday night through next weekend, with the most likely
  chances appearing on Thursday

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 221 PM CDT Mon May 13 2024

Ongoing widely scattered showers and storms will gradually become
more widespread and continue over the next several hours as a
southern stream upper-level jet continues to lift northeastward
towards our region from the southern Plains. A cut-off upper low
will translate over our region this evening through Tuesday. As the
previous forecast discussion mentioned, instability and shear will
be very marginal, with effective shear values progged around 20
knots or less, with HREF surface based CAPE up to 1000 J/kg this
afternoon. Given this parameter space, severe storms aren`t
expected. However, with Pwat values hovering around 1.2 to 1.4,
which is near or above the 90th percentile off the SPC sounding
climatology, periods of heavier rainfall are expected. A deformation
zone appears to develop north of the cut-off low, and pivot across
our southern forecast area. Slow moving or repeated rounds of
showers and storms would allow rainfall to accumulate rapidly, so we
will continue to watch for flooding issues. WPC continues to paint a
Slight risk of flash flooding for areas along and south of
Interstate 80. In total, between 1 to 2 inches of rainfall remains
possible for areas along and south of I-80, with gradually lighter
amounts farther north. HREF localized probability-matched mean
indicates some isolated areas could see between 2 to 3+ inches of
rainfall, given the higher Pwat values.

As we go into Tuesday, the deformation band is expected to weaken
with time, but it won`t move a whole lot, so showers will continue
to linger across our southern forecast area. Eventually, the upper
low will move off to the east by late in the day Tuesday, which will
bring any lingering showers to an end and lead to decreasing cloud
cover from the northwest. One other thing to watch for, especially
in the afternoon hours Tuesday, is the potential for some Canadian
wildfire smoke to filter in from the north. Air Quality Alerts have
been issued for areas of northern Iowa into Minnesota and Wisconsin.
The HRRR Smoke model shows a smoke plume dissipating as it filters
into our region, but the impacts from this smoke are expected to
be little, if any, at this time.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 221 PM CDT Mon May 13 2024

The long-term period starts off with dry conditions for Tuesday
night through Wednesday, thanks to an area of high pressure nosing
into the region from Ontario Canada. Temperatures will be seasonal
for this time frame, with lows Tuesday night in the middle to upper
40s, and highs Wednesday in the lower to middle 70s.

The next chances of widespread showers and storms returns for
Thursday as an upper-level trough translates eastward across the
central Intermountain West region. A southern stream mid-level
impulse is progged to lift northward towards our region, and bring
widespread chances (40 to 70% from the NBM) of rainfall. Pwat values
of around 1 to 1.3 inches are progged off the deterministic GFS and
NAM guidance, so another round of decent rainfall is possible
Thursday, although NBM probabilities of total rainfall of a quarter
inch or greater is between 40 to 60 percent, so not a strong signal
either way. At this time, the threat for any strong to severe storms
Thursday remains low, given meager values of effective shear and
instability.

The upper-level pattern continues to be active into the end of the
week, with additional upper-level troughs traversing the northern
CONUS, but confidence in the timing of these troughs for our area
remains uncertain due to differences in the guidance.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1245 PM CDT Mon May 13 2024

Mostly VFR and dry conditions were observed across the area as
of TAF issuance. However, this is not expected to last too long,
as an area of low pressure lifts northeast towards the area,
which will support more widespread chances of showers and storms
later this afternoon. Confidence in the storm coverage is low,
given differences among the high-resolution models, but I am
confident that any storms will result in heavy downpours and
brief IFR conditions. After sunset, models are in good agreement
with lowering ceilings to MVFR this evening, and eventually to
IFR after midnight. There is expected to be a brief lull in
precipitation before more rain develops late Tuesday morning
over BRL and MLI.

&&

.HYDROLOGY...
Issued at 221 PM CDT Mon May 13 2024

New forecasts by the North Central 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 rain falls this afternoon
into this evening, 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
morning. 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.

Flood Watches have been issued for the Mississippi River at
Gladstone and Burlington due to routed flow as well as rainfall
amounts forecast through Tuesday.

Taking a deeper dive into the QPF, widespread rainfall in the 0.5"
to 1.5" 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, Cedar, and Mississippi 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...Schultz
LONG TERM...Schultz
AVIATION...Schultz
HYDROLOGY...Cousins