Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 171555
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1055 AM CDT Sun Sep 17 2017

.UPDATE...
Issued at 1051 AM CDT Sun Sep 17 2017

Without convergence, forcing, and favorable timing for convection
along a cold front, the rains faded to nothing before crossing the
Mississippi River. I have updated to dry the forecast out through
Midnight tonight. In the wake of the dissipating cloud cover
today, the main question will be on how much we can heat up in the
cold advection regime. Given the very mild start for the
southeast 2/3rds of the CWA, I think the 70s are still a good fit,
but the northwest corner may remain in the upper 60s. That will
be the focus of any additional forecast updates today.

&&

.SYNOPSIS...
Issued at 330 AM CDT Sun Sep 17 2017

Incoming cool front was currently pushing acrs the northwestern
third of the DVN CWA, with associated clusters of showers and
embedded thunderstorms streaming up along it and mainly post-
frontally. Aloft, mid and upper level moisture flow patterns on the
current water vapor loop was indicating a rather strong short wave
trof rolling northeastward acrs the Dakotas and western MN.  After
the frontal passage and precip chances pass this morning, the mid
and upper flow pattern projected to de-amplify/flatten some acrs the
mid CONUS into early this week. The LLVL boundary will get caught up
parallel and try to retreat north Mon into Tue, with precip chances
increasing again acrs the area in the process.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Sun Sep 17 2017

Today...Will walk the incoming showers/storms east acrs the rest of
the DVN CWA through 9-10 AM CDT, but signs of better llvl moisture
convergence and support should make for more widespread
showers/storms moving acrs MO to the south, which may rob to the
north as the morning progresses. This may make for waning trends in
both strength and coverage through the next 3-5 hours as the
convection sweeps east acrs the local area. But until then, there
may be better coverage developing along and south of I80 as the
south central IA into southeastern IA showers/storm clusters
propagate eastward. If some of the upstream precip can maintain it`s
current strength for just awhile as it moves in, extent of moisture
saturation and PWAT feed supports localized swaths of a 0.50 inch to
close to an inch. Most other areas that manage to get under a
passing precip cluster to get 0.15 to 0.30 or less through mid
Sunday morning. After 10-11 AM just see some lingering showers
through late morning/midday southeast of a line from Keosauqua in SE
IA, to Burlington IA, and to Princeton IL. Several of the latest
HiRes CAM runs support this idea as well, with maybe a temporary mid
to late morning uptick in these areas just behind the passing front
before LLVL convergent flow fully veers.

Then as the front sags south and east of the area and high pressure
builds in from out of the northern plains, the afternoon should be
mainly dry with clearing skies especially along and north of I80.
Cooler post-frontal highs today mainly in the 70s. the models may be
under doing sfc winds from the north-northwest this afternoon in
incoming high pressure gradient, but for now will not stray too far
off.

Tonight...the first half of the night to be dry, but then the next
upstream vort max lurks acrs the east central plains in cyclonic
curving west-southwesterlies pushing east acrs the MO RVR Valley.
Increasing lift/isentropic motions along and north of a llvl front
draped west-to-east acrs northern MO along with elevated moisture
feed, should help more showers and even a possible elevated
thunderstorm to peculate and increase acrs the southwestern third
of the CWA after Midnight into early Mon morning. Will adjust POPs
accordingly, and go with cool overnight lows down in the 50s. Some
northern areas/Hwy 20 corridor will have the potential to dip into
the upper 40s if high clouds off the next "weather maker" delay in
thickening until late acrs those areas.    ..12..

.LONG TERM...(Monday through next Saturday)
ISSUED AT 330 AM CDT Sun Sep 17 2017

The good news is the pattern will become more active and feature
rain chances, as a longwave upper trough forms in the western
CONUS and a ridge strengthens over the eastern CONUS and
potentially evolves into a Rex block as one or more tropical
systems undercuts the ridge. The bad news... I don`t foresee
any real significant or drought busting rains, and while the
forecast will have nearly daily chances for rain realistically
this will likely boil down to just a couple days or so. The
first of these rain chances will be arriving Monday lingering
into Monday night. In fact, guarded optimism exists on the
likelihood of rain and also being fairly widespread given synoptic
lift enhanced by right entrance region of 100+ kt jet streak
over the Upper Midwest. In addition, a mid level shortwave is
depicted along with decent moisture advection north of a stalled
boundary to our south. Rainfall is likely to be mostly around
0.25 to 0.5 inch... or less. The boundary to our south is shown
to lift back north as warm front on Tuesday. However, increasing
heights aloft will likely limit rain chances with this front.
Midweek may then harbor our next better chance for rain, although
do have concerns this could trend drier given main height falls and
upper jet and attendant synoptic lift passing well to our north/west.
Then by next weekend may come another better chance for rain due to
increasingly meridional flow ahead of deep western CONUS trough
aiding advection of deep moisture into region ahead of next frontal
system. However, if Rex block develops and slows eastward progression
of systems this moisture plume and front, and subsequent better rain
chances could end up further west while we would be more governed
by dry Great Lakes high pressure.

As for temps, Mon-Tue likely to be coolest of the period and offer
challenges due to clouds/rain Mon and then movement/timing of warm
front. By mid to late week a warming trend back above normal is
anticipated with a deepening southerly flow.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday Morning)
ISSUED AT 649 AM CDT Sun Sep 17 2017

Decaying area of showers may make for temporary MVFR conditions at
MLI and BRL through 10 AM, but otherwise improving CIGS and VSBYS
into the afternoon. A lingering post-frontal low MVFR deck at CID
and DBQ accounted fro as well through mid to late morning, before
high pressure moves in. Winds to continue to veer to the northwest
and north today with speeds of 8-13 KTS, before decreasing to
around 5 KTs or less by this evening. Mid to high clouds will
thicken from the west again later tonight into early Mon morning,
with light east to northeast sfc winds. A low chance for a high
based/elevated shower or thunderstorm to move east and get into
the VCNTY of BRL after 5 AM CDT Mon morning...for now will keep
TAFs dry tonight through 12z Mon.   ..12..


&&

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

$$

UPDATE...Ervin
SYNOPSIS...12
SHORT TERM...12
LONG TERM...McClure
AVIATION...12


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