502
FXUS63 KDVN 252006
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
306 PM CDT Sat May 25 2024

.KEY MESSAGES...

- Another storm system will bring more storms that have the
  potential to be strong to severe on Sunday.

- A change in the flow pattern aloft is expected to bring a period of
quiet weather for much of the coming week.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 304 PM CDT Sat May 25 2024

Dry and pleasant conditions will be seen across the area through
midnight. Attention then turns to the late night hours and Sunday.

After midnight return moisture and forcing will induce a band of
showers and thunderstorms west of the Mississippi that will move
northeast. Right around or just before sunrise additional
development will occur along the Mississippi that also moves
northeast during the morning. The development along the Mississippi
will be induced by the approaching weak surface low.

The overall time frame for this looks to be 2 to 10 AM. The overall
severe risk currently looks low with hail being the primary risk and
wind a secondary risk.

After 10 AM Sunday there will be a minima in shower and thunderstorm
activity as mid level lapse rates are fairly stable. While isolated
showers and storms will be possible the key message is that much of
the area could be dry from late morning through early afternoon.

By mid-afternoon diurnal convection will develop along the residual
boundaries left over from the overnight/morning convection. The main
boundary for this new convection looks to be in Missouri where a
nocturnal storm complex lays out a stout boundary. However,
additional boundaries further north combined with differential
heating will allow isolated to scattered storms to develop.

Based on current information areas south of I-80 look to have the
better areal coverage at 35 to 50 percent. North of I-80 areal
coverage will be lower, potentially only in the 15 to 30 percent
range.

The overall severe risk Sunday afternoon is conditional. That is it
will be dependent upon how the overnight and morning convection
evolves. The better risk for any severe storms Sunday afternoon does
look to be south of I-80 which matches the CSU severe probabilities.
The primary risks look to be hail and wind. However, any storm that
interacts with a pre-existing boundary would have the potential for
a brief tornado.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Issued at 304 PM CDT Sat May 25 2024

Sunday night through Tuesday
Assessment...medium to high confidence

Diurnal convection that develops Sunday afternoon will continue into
Sunday evening before dissipating. While areal coverage is not high
(20-40 percent with the better chances east of the Mississippi),
this time frame has the highest confidence of occurring.

Late Sunday night into Monday morning looks to be dry as high
pressure moves through the area.

Monday afternoon a weak upper level disturbance will move through
the area. The model consensus has a 20-40 percent chance of rain
occurring with the better chances across the highway 20 corridor.
However, moisture availability will be the key as to whether or not
any rain occurs. Several deterministic model runs suggest little if
any rain but there are several ensemble members from the various
models suggesting rain. Thus the rain chance is based on the
ensemble members.

Monday night look to be dry as high pressure moves east of the area
and the upper level ridge begins to move east from the Plains.

Tuesday is the most questionable day for rain chances and thus the
lowest in confidence.

Heights aloft are slowly rising which is usually a negative for
rain. Moisture also looks to be lower which would also not favor
rain. However, there are some ensemble members of the various models
suggesting rain for the area. The overall rain risk is low (20-25
percent) and is north of a line from Independence, IA to Kewanee, IL.

Given the few ensemble members suggesting rain, the possibility does
exist that Tuesday could end up being dry for the entire area.

Tuesday night through Thursday
Assessment...high confidence

The global models build an upper level high across the area which
will bring dry conditions and temperatures trending above normal.

Thursday night through Saturday
Assessment...medium confidence

The global models agree that active weather will return again late
next week.

Right now it appears there may be two systems but there is
disagreement on their respective timing. As a result of the timing
disagreements, the model consensus has a risk of rain in each period
from Thursday night through Saturday.

Based on the overall chances for rain, the Friday afternoon through
Saturday time frame appears to be favored with rain chances at 30 to
40 percent.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1241 PM CDT Sat May 25 2024

VFR conditions will be seen through 06z/26 as high pressure
moves into the Great Lakes. After 06z/26 a band of SHRA/TSRA
will develop across eastern Iowa with further development along
the Mississippi River toward 11z/26. Outside of this band VFR
conditions will be seen with MVFR/IFR in SHRA/TSRA. After 12z/26
SHRA/TSRA will gradually end across eastern Iowa but more
widespread MVFR conditions are expected.

&&

.HYDROLOGY...
Issued at 1025 PM CDT Thu May 23 2024

The flood warning for the North Skunk River near Sigourney has
been upgraded to Major flood category. Routed water from a
sparse data area upstream where the heaviest rain fell a few
days prior has led to a rapid rise in the last 6 hours and is
now above Major flood stage. The forecast calls for a crest of
24.5 feet by Friday afternoon, but there is uncertainty in the
amount of water that remains to move through the reach and the
crest may need to be further adjusted.

The Wapsipinicon River near DeWitt was upgraded to a Flood
warning. Major flood stage is being forecast based on routed
flow, and is supported in output from the Hydrologic Ensemble
Forecast Service Model Simulation (HEFS), which places high
confidence on reaching Major Flood stage (12.5 feet). The
forecast has gone up this evening with a crest now over 13 feet
next week. This fits near the most likely range from HEFS of
12.8-13.1 feet. Some attenuation is possible as the routed
flow moves through the river system, but at the same time there
will be additional rounds of rain Friday and Sunday of which
could total over 1 to 2 inches. There will likely be changes to
the forecast in the coming days as the rain lays out and the
extent of the routed flow is better known, so stay tuned!

Routed water and additional rain through the weekend is leading
to rises on most other tributary rivers and the mainstem of
the Mississippi, especially south. Flood warnings or watches
are in effect for portions of the Cedar, Iowa, Skunk and
southern sections of the Mississippi river so please refer to
the latest Flood Statements and Flood Warnings for details.

&&

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

&&

$$

SHORT TERM...08
LONG TERM...08
AVIATION...08
HYDROLOGY...McClure