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000
FXUS63 KDVN 091026
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
526 AM CDT Sun May 9 2021

...12Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 321 AM CDT Sun May 9 2021

Rain continues, and remains widespread early this morning within
strong mid level frontogenetical forcing along elevated front north
of surface boundary to our south. Some embedded convection is
occurring mainly along/south of Hwy 30 within MUCAPE gradient and
ribbon of convergence with impinging 35-45 kt low level jet.
Radar has shown some pronounced bright banding at times on the
northern fringes of the rain shield indicating melting snow a few
thousand feet up, which has led to anomalously high reflectivity at
times. The rain has been moderate to heavy in the strong forcing and
moisture feed with PWATs over 1 inch. Rough estimates of around 0.5
inch to over 1 inch of rain has already fallen in many portions of
the area, with a very tight gradient and lower amounts along and
north of Hwy 20 corridor.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 321 AM CDT Sun May 9 2021

Tale of two halves of the day for today, with rain to start and then
some peaks of sun (hopefully) to end. Mid level FGen circulation
will begin to shift east of the area after daybreak, and will bring
about an end to the rain from W/NW to E/SE through midday. The
hope is with the ensuing subsidence and waning of the bowing MCS
well to our south, that we`ll see some thinning of the high
cloudiness and overall some decrease in clouds leading to sun
peaks for the afternoon. That said, steep low level lapse rates
depicted in forecast soundings will likely foster cumulus
development with any sun peaks, so the sunshine may not be
prolonged. In addition, a weak mid level wave diving down in the
flow will also look to bring some mid cloudiness initially north
late this afternoon and can`t rule out a spotty light shower as
well. But, overall should be a dry afternoon albeit still breezy
and seasonably cool with highs mainly in the 50s. Areas north/west
of the Quad Cities where more sunshine and deeper mixing is
favored could see highs around 60 degrees.

Tonight, winds should diminish with sunset. Some mid cloudiness will
likely traverse the region in response to the passing wave. A few
sprinkles or stray light shower is possible, but plenty of dry air
is noted in the column and as such measurable potential appears too
low for any mention. Forecast lows have inched up a bit due to the
increased signal for some cloudiness around, with generally upper
30s and lower 40s. With the light winds will have to monitor cloud
cover closely, as should it decrease then it would likely be cooler
with a potential for some frost.

.LONG TERM...(Monday through Saturday)
ISSUED AT 321 AM CDT Sun May 9 2021

Key Messages:

1) Slight chance of PM rain shower Monday, otherwise dry through mid-
week with continued cool temperatures.

2) Chance of precipitation towards the end of the week with
temperatures moderating to near normal.

Monday through Thursday...

Much of the period will be dry as we will be under the influence of
surface high pressure building in from the upper Mississippi River
Valley. The exception will be Monday afternoon, as guidance is
beginning to zero in on a weak shortwave from a rotating 500 hPa low
north of the Great Lakes moving into the area. This may be enough to
steepen lapse rates and trigger some instability rain showers, but
it`s not expected to be widespread in coverage. Therefore, am only
going to be advertising slight chance POPs in this forecast package.

With northerly flow still dominating, temperatures will remain on
the cool side. Look for highs in the upper 50s to mid 60s, and
overnight lows in the low to upper 30s. Depending on cloud cover and
the magnitude of winds, this may lead to areas of frost Monday
night/Tuesday morning.

Thursday on...

Rain and storm chances are beginning to get pushed more towards late
this week in the latest model runs, with most deterministic guidance
not having anything impacting our area until at least Friday. Given
the disagreement still on the shortwave track and QPF placement, not
confident on going POPs any higher than chance at this point.

What remains high confidence is our temperature forecast, as the
surface high moves into the northeast U.S. and southerly flow
returns to the area. Highs in the upper 60s to 70s are likely just
in time for the weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday Morning)
ISSUED AT 525 AM CDT Sun May 9 2021

Improvement to VFR expected today and lingering tonight, as the
rain and attendant IFR to MVFR conditions continue to dissipate
this morning with the storm system exiting the region. Northeast
winds will remain gusty at times at 15-30 kts today then become
light and variable with sunset. An upper level disturbance
dropping down across the area tonight will bring some mid clouds,
and the low chance for an isolated light shower or sprinkles but
left out mention due to limited coverage and negligible impacts.

&&

.HYDROLOGY...
Issued at 321 AM CDT Sun May 9 2021

Bright banding has led to unrealistically high reflectivity values
at times south of Hwy 20 to Hwy 30 corridors. This has resulted
in a substantial radar overestimation of rainfall amounts,
especially over the Maquoketa River basin, upper portions of the
Cedar, Iowa and Wapsipinicon basins, and also the Mississippi
River between Bellevue L/D 12 and Camanche. Based on other
observational data and a few spotter reports, it appears that
most areas south of Hwy 20 have seen between 0.5 inch to 1.5
inches of rain so far. Before the rain ends this morning there is
the potential for a few areas to possibly see totals of near 2
inches south of I-80. A Flood Watch remains in effect for the La
Moine River at Colmar due to the forecasted rainfall of 1 to 2
inches. Confidence is somewhat lower on these higher amounts
occurring over this basin at this time. Given the dry conditions
leading up to this rainfall, anticipate predominantly within bank
rises on area rivers.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...McClure
SHORT TERM...McClure
LONG TERM...Speck
AVIATION...McClure
HYDROLOGY...McClure