Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 100449

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1149 PM CDT Mon Oct 9 2017


Issued at 320 PM CDT Mon Oct 9 2017

A front extended across Missouri into northern Illinois during the
afternoon. Near and south of the front, temperatures reached the
low 80s around Macomb. North of the front, readings were in the
upper 60s near Independence. Clouds increased during the
afternoon, along and east of the Mississippi River, while eastern
Iowa was mostly clear.


.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 320 PM CDT Mon Oct 9 2017

The main forecast issues in the short term period are rainfall
amounts and coverage, and potential for isolated severe weather
and flash flooding.

In the near term, the NamNest and HRRR have hinted at a few
showers developing in the enhanced CU field over the far southeast
counties during the late afternoon. Have opted to keep forecast
dry for now and monitor short-term trends. Later this evening,
expect an increasing N/NE wind as surface low pressure approaches
the region. Have held off any showers until after midnight, per
consensus model timing. Areas along and south of I-80 would be
favored for rain through 12z.

Tuesday morning, showers and scattered storms forecast to increase
in coverage from south to north. There are some variations in the
main surface low track, with the ECMWF still the farthest
northwest. The 500mb low tracks are similar. The ECMWF continues
to be very consistent with track and bullish QPF output. WPC has
the forecast area in the day 2 marginal risk area for excessive
rainfall. Am thinking most areas can take a good amount of rain
with no issues, but will have to monitor urban areas affected by
very high rainfall rates.

Regarding severe weather potential, there are a number of factors
that raise some red flags. This will be another unseasonably moist
airmass, with PWAT values above 1.5 inches. A potent negatively
tilted 500mb wave is concerning. The key may be if enough MUCAPE
develops, to complement the large level shear/helicity and
favorable 0-3km shear vectors. CAMS are indicating at the very
least, some strong storms will be an issue Tuesday morning and
again during the afternoon. Straight line winds and brief HSLC
tornadoes would be the main threats with this potentially volatile
set-up. The farther NW ECMWF solution would mean more of the
southeast counties exposed to this risk. Confidence in these
scenarios is typically low a day in advance, but we will be
monitoring closely.

.LONG TERM...(Tuesday Night through Monday)
ISSUED AT 320 PM CDT Mon Oct 9 2017

The next storm system moves through Tuesday night and exits the area
Wednesday morning. A general rain across the area is expected with
some embedded thunderstorms early Tuesday evening. The best chances
for rain look to be Tuesday evening with rain slowly ending from
southwest to northeast late Tuesday night into Wednesday morning.

Dry conditions are expected Wednesday afternoon through Thursday as
high pressure builds into the Midwest. The models are suggesting the
potential for a layer of moisture becoming trapped which, if
correct, suggests plenty of low clouds Wednesday night and Thursday.

Thursday night on...

Thursday night/Friday the model consensus has dry conditions for the
area as high pressure moves into the eastern Great Lakes.
Temperatures will average above normal.

Starting Friday night and continuing through Sunday a period of
unsettled weather looks to be in store for the area. The models
bring another front into the area that stalls. While the front is
stalled, another storm system will ride up along the front bringing
another widespread rain event for the area.

There are timing differences on when the storm system will move up
along the stalled front. The ECMWF suggests Saturday night/Sunday
while the GFS suggests Saturday/Saturday night.

There are also questions regarding moisture availability when the
front initially arrives in the area Friday night. The arriving storm
system will bring a slug of moisture with it so rain chances would
be higher when it moves through the area.

As a result of the timing differences, the model consensus has
chance pops Friday night, likely to categorical pops
Saturday/Saturday night, and chance pops on Sunday.

Sunday night/Monday the model consensus has dry conditions for the
area as high pressure moves through the Midwest.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
ISSUED AT 1133 PM CDT Mon Oct 9 2017

Conditions expected to become predominately MVFR Tuesday in low
clouds and bouts of rain/showers lingering through Tuesday
evening, as a storm system lifts into the Mid-Mississippi Valley
region. Anticipate MVFR arriving in the morning at BRL, toward or
around midday at MLI, and PM at CID and DBQ. Some pockets of IFR
conditions possible later in the afternoon/evening, mainly due to
visibility in the stronger showers. Also, some thunder is possible
mainly near BRL and south/east but too low of risk for mention.
Winds will become gusty at 10-20 kts from N/NE.




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