Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 091951
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
251 PM CDT Sun May 9 2021

.SYNOPSIS...
Issued at 151 PM CDT Sun May 9 2021

The surface low with last nights storm system has moved into the
MIddle Ohio River Valley. Thick clouds associated with that storm
system spread across the southern third of our area with scattered
cumulus spreading across the northern half. Temperatures at 2 PM
ranged from 47 degrees at Macomb to 61 degrees at Vinton.
Dewpoints ranged from lower 30s across far northwest Illinois to
the mid 40s in parts of east central Iowa. Northeast winds of 15
to 25 MPH continued across the area.

&&

.SHORT TERM...(This Evening through Monday)
ISSUED AT 151 PM CDT Sun May 9 2021

The main forecast concern are a slight chances of precipitation
late Sunday night into Monday. Models differ in the strength of a
shortwave rotating around a 500 MB trough that will impact the
short term forecast.

A 500 MB low will slowly wobble from southern Canada into the
Upper Great Lakes over the next 24 hours. At the surface, a week
surface low currently sits in central Wisconsin with a trailing
convergence zone along the Interstate 94 corridor into eastern
North Dakota. This surface low will move into central Illinois as
a shortwave rotating into the base of the 500 mb trough moves
across the Lower Great Lakes. Clouds will overspread eastern Iowa
and northwest Illinois ahead of this feature tonight into the day
on Monday. The NAM is very aggressive with strong lift across
northwest Illinois in the 9 to 12 UTC MOnday while the GFS and
others have weaker lift across the area. Have put 15 POPs across
this area for early Monday morning. As this weak low and
convergence line shifts southward through the day on Monday,
daytime heating and lift will bring scattered showers to the area
south of Interstate 80.

Removed patchy frost from the forecast for early Monday morning
as moisture from recent rains will allow dewpoints to rise as the
atmosphere decouples tonight resulting in lighter winds. This in
conjunction with increasing clouds will keep low temperatures in
upper 30s and lower 40s across the area. High temperatures on
Monday will be 1 to 2 degrees warmer than Sunday.

&&

.LONG TERM...(Monday Night through Sunday)
ISSUED AT 151 PM CDT Sun May 9 2021

.Long Term...Monday night through next Sunday...

1. A gradual change from below normal conditions to near normal
temperatures is expected through the extended forecast.

2. Precipitation chances return to the forecast late in the week.

A broad upper trof will continue to reside over the Great Lakes
through Tuesday.  Surface high pressure will be found just north of
Iowa Monday night, then it will settle south and remain over the
local area through Thursday.  This process will bring wide diurnal
spreads and cool weather through Tuesday, followed by gradual
warming. While this process will be dry for the most part, some
cumulus will be possible Tuesday with the cool air aloft.

The upper trof is forecast to move east by Thursday night, resulting
in a transition to northwest flow over the Midwest. This process
will set up warm advection over the Plains, and may allow for
elevated showers and some thunderstorms spreading in from northwest
Iowa beginning Friday.  For now, pops are in the lower to moderate
chance range for this late week threat, as we cannot be certain of
any placement of the warm front aloft, nor the timing of any short
waves in northwest flow this far out.

Certainty is much higher that we`ll see temperatures climb to near
normal, with highs in the lower to mid 70s over the CWA by the
upcoming weekend.

ERVIN

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
ISSUED AT 1226 PM CDT Sun May 9 2021

The storm system that brought rain, MVFR to IFR ceilings, and
gusty northeasterly winds to eastern Iowa TAF sites is moving off
to the east. Some uncertainty exits over the next 2 to 3 hours in
the timing of wind speed decreasing and the ceilings lifting to
VFR for the remainder of the day. When I wrote the TAFs, I had
both MLI and BRL lifting to VFR in the 20 to 21 UTC timeframe.
There may be some fluctuation up and down until the ceilings do
lift to VFR and remain there through the remainder of the period.
Mid level clouds with ceiling around 9kft will move back into the
area tonight into Monday morning as a disturbance slips by to our
northeast. Showers are possible as this wave passes by but
confidence is low that any shower would impact KDBQ at this time.


&&

.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...Cousins
SHORT TERM...Cousins
LONG TERM...Ervin
AVIATION...Cousins
HYDROLOGY...McClure


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