062
FXUS63 KDVN 221816
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
116 PM CDT Wed May 22 2024

...Midday Hydrology Update...

.KEY MESSAGES...

- Dry conditions for most today, with seasonable temperatures
  and comfortable humidity. There is a slight chance (15%) of a
  shower/storm along of north of Hwy 20 in Iowa this afternoon.

- Active weather returns by Friday and again early next week
  with increasing shower and thunderstorm chances. There is a
  Marginal Risk (level 1 of 5) for severe weather on Friday.

- The Cedar, Iowa, Skunk, and the Wapsi rivers are expected to
  rise with some sites going into flood in the next 3-4 days
  due to the recent 2-5 inch rainfall upstream.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 1205 PM CDT Wed May 22 2024

A beautiful early afternoon was unfolding across all of eastern
Iowa, northwest Illinois and far northeast Missouri; a nice
welcome after yesterday`s active weather. Skies featured mostly
sunny skies with temperatures as of noon ranging from the mid
60s to near 70. It was breezy as well with west to northwest
winds gusting around 20-30 MPH.

15z surface analysis showed a strong surface low just north of the
arrowhead of Minnesota, with high pressure in place across the
central Plains. The pressure gradient between the low and high was
rather tight and, along with deep boundary layer mixing, was
responsible for our gusty winds early this afternoon.

Over the next 24 hours, our weather will be influenced by the the
surface high as it slowly moves across the Plains into the mid-
Mississippi River Valley. Gusty winds will subside late this
afternoon and evening, becoming light & variable tonight into much
of Thursday. Skies will feature only a few clouds, allowing for more
of a diurnal swing to our temperatures compared to previous
days. Look for lows tonight in the low to mid 50s (some upper
40s possible in valleys and low-lying areas), with highs
Thursday recovering into the upper 70s to lower 80s ahead of
strengthening ridging aloft.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 305 AM CDT Wed May 22 2024

Thursday...quiet and dry conditions will be seen with 850mb
temps warming to 13C and southeast return flow boosting
afternoon temperatures into the upper 70s and low 80s.

Thursday night-Friday...00z models and their ensembles all show
a strong upper level wave moving into the northern Great Plains,
with diffluent flow developing over the Midwest. Another cold
front will track east across Iowa with strong moisture
transport expected ahead of it (PWs increasing to 1.5") into
the local area. Sufficient shear and instability will present a
risk for some stronger storms to develop in the warm sector
which may again be over the local area. For this reason, SPC has
a Day 3 Marginal (level 1 of 5) risk for severe weather across
the entire outlook area. Timing of the fropa will be critical as
to what impacts may be seen Friday. The 21.00z run of the Pas
Ensemble shows a wide range of solutions ranging to a few
storms, a large line of storms, and no storms. Needless to say
more details need to be ironed on before Friday. Stay tuned.

This Weekend and Memorial Day...00z ensemble data continues to
show Saturday as a cooler and drier day across the CWA. Highs
in the 70s and lows in the 50s are forecast. The latter half of
the weekend and into the holiday is trending more active with
two main waves moving through. Will maintain the daily chance
PoPs through Monday night, but my confidence in each period
seeing rainfall is low and some dry hours should be seen. One
thing is for certain, it does not appear to be a hot and humid
Memorial Day.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1205 PM CDT Wed May 22 2024

VFR conditions are expected for the upcoming TAF period. Gusty
west to northwest winds around 20-25 kts will become light &
variable with high pressure moving in this evening.

&&

.HYDROLOGY...
Issued at 115 PM CDT Wed May 22 2024

Watch/Warning Changes this Morning:

Upgraded the North Skunk River at near Sigourney to Major flood and
added the English River at Kalona to a warning with a secondary
crest into Minor. Also went to a warning for minor flood category
for the Wapsi at Anamosa.

Discussion:

Rainfall in the past 24 to 36 hours was highest in the Iowa and
Skunk river basins near their headwaters where radar estimates and
automated gauges reported 2 to 5 inches. The Cedar and Wapsi also
received 1.5 to 3 inches in the upper portions of the basins.
Because of this, the Iowa River at Marengo and the Skunk River near
Sigourney have the best chances of reaching solid Moderate Flood by
the end of the week. In fact with a projected run-off boost, there
was enough confidence to upgrade the North Skunk to Major flood
category. But still the idea that these sites will likely see some
attenuation in the routed flow upstream and expect some changes to
the forecast in the coming days. Because of this, confidence is
lower at some other sites in reaching the currently modeled flood
crest and Flood Watches were either continued or held off for one
more shift to assess. A few examples are the potential crest into
the Major category on the Wapsi near De Witt, and maintain the watch
for the Cedar River at Conesville for now. Oakville on the Iowa
River may eventually need a watch with crest projections near the
flood stage by late Monday night.

&&

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

&&

$$

SHORT TERM...Speck
LONG TERM...Gross
AVIATION...Speck
HYDROLOGY...12