387
FXUS63 KDVN 121708
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1208 PM CDT Mon Aug 12 2024

.KEY MESSAGES...

- Showers and a few storms today, especially this morning with
  the greatest chances (60-80%) west/south of the Quad Cities.

- Fog /some dense/ is possible tonight, particularly in areas
  that see rain today.

- More widespread showers and storms with a threat for heavy
  rain expected midweek.

- Temperatures near seasonal averages by mid to late week.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 315 AM CDT Mon Aug 12 2024

A strong geomagnetic storm brought out the Aurora Borealis /
Northern Lights last evening into the overnight, with it
visible across parts of the area. But now, clouds continue to
increase/thicken ahead of an approaching shortwave, which is
aiding a burgeoning area of showers and some storms across
western into central Iowa. As this system translates E/SE
today, we can expect showers and a few storms to move across
the area, particularly this morning mostly from around Hwy 30
on southward. The heaviest QPF is anticipated across far SE
Iowa, NE Missouri and perhaps portions of WC Illinois where
the better potential for storms will be found and where the 00z
HREF LPMM indicates the potential for pockets of 0.5 to 1 inch.
We may see additional scattered showers and storms develop
this afternoon into early evening mainly near and south of Hwy
30, along a differential heating boundary as the primary
vorticity lobe passes. While severe weather is not currently
anticipated, as always this time of year with boundaries and
vorticity we`ll have to be monitoring for funnels.

Highs today will be very challenging. Where the clouds
and precipitation linger (favoring the far southern service
area) highs will likely be limited into the upper 60s to around
70. Meanwhile, areas that manage to see more in the way of
sunshine (favoring north/east of the Quad Cities) will likely
get a boost into the mid/upper 70s for highs, and if more sun
than anticipated there could be some lower 80s as suggested by
some guidance.

Surface to mid level ridging will begin to build back in later
tonight heading toward midweek. The light flow and decreasing
clouds may lead to some fog, particularly in areas that see rain
today which could foster pockets of dense fog. Generally dry
and near seasonable conditions are expected Tuesday and Tuesday
night, with ridging more dominant holding the main boundary and
convective spawning grounds just to our west and south.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 315 AM CDT Mon Aug 12 2024

A strong wave and favorable jet dynamics look to enhance the
large scale lift across the region Wednesday/Thursday, bringing
the likelihood (60-80%) of widespread rainfall, which could be
heavy. This timeframe continues to be highlighted by WPC, with
a slight risk for excessive rainfall across much of the service
area from 12z Wednesday to 12z Thursday. Current timing seems
to start Wednesday afternoon, with increasing coverage through
the night and Thursday. The best moisture arrives by Thursday,
which is resolved well amongst guidance, hinting at upwards to
2.00" PWATs or higher. Given our past heavy rainfall events this
summer, I am not quite sure that we will go much higher than
that 2.00" PWAT, as we have underperformed compared to guidance
prior. In either case, PWATs between 1.50-2.00" are near or
greater than the 90th percentile in climatology, indicating that
we can expect heavy rain with any thunderstorms. The strength
of the dynamics/forcing suggests we could see some areas wring
out all of the PWAT and then some to the tune of 2+ inches of
rain. NBM probabilities are 50-60% across a good portion of the
area for seeing at least 1 inch or more of rain in the 24 hours
ending 12z Thursday. It has been very dry to start the first 11
days of August with negative soil moisture anomalies, but
despite this we can`t rule out at least a localized flash flood
threat with any repetitive convection given the anomalous
moisture and strength of forcing. The severe weather threat
appears low, but will have to watch for an elevated hail threat
Wednesday night with the ramping LLJ given 30-35+ kts of 0-6 km
shear. Then later Thursday we`ll still have to keep tabs on a
possible pseudo triple point with some surface based threat,
but this is very conditional upon location/timing and sufficient
destabilization.

Temperatures will be near normal mid to late week, but heading
into the weekend temperatures may not be as warm as advertised.
The GFS and ECMWF both cut the upper low off over the Great
Lakes region, with our area under the western flank of the
system. Thus, we would fall under largely northerly to
northwesterly flow Friday and through the weekend. This would
put us under cold advection and keep the chance for possible
wrap-around precipitation into the weekend. Thus, the weekend
might trend a bit cooler than normal and remain gloomy. Stay
tuned, as these details become better defined over the next few
days.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1201 PM CDT Mon Aug 12 2024

VFR conditions will prevail through much of the TAF period, with
the potential for fog late tonight, bringing in MVFR to IFR vis.
Through the day today, winds will remain light and out of the
southeast, becoming light and variable throughout the area
tonight. BRL may see some isolated showers through the
afternoon and evening, but confidence remains low on that and
the overall impacts. Otherwise, the main concern will be the
potential for fog tonight throughout the area. Generally
between 08-12z, we should start to see fog develop, with the
potential for dense fog in low-lying areas and river valleys.
Currently, confidence is low on the overall coverage of fog
tonight. Rather, it is currently being messaged as 2SM and BR.
This will continue to get updated over the next couple of
forecasts.

&&

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

&&

$$

SHORT TERM...McClure
LONG TERM...McClure
AVIATION...Gunkel