Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 082348
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
548 PM CST Thu Dec 8 2016

...00z AVIATION UPDATE...

.SYNOPSIS...
Issued at 243 PM CST Thu Dec 8 2016

18Z surface data has high pressure over the Plains with a weak trof
moving through the Great Lakes. Dew points were in the 20s across
the Great Lakes with single digits and teens above zero across the
remainder of the Midwest.

&&

.SHORT TERM...(This Evening through Friday)
ISSUED AT 243 PM CST Thu Dec 8 2016

A passing upper level disturbance was providing just enough forcing
on the available moisture to produce isolated to scattered flurries
this afternoon. The clouds and flurries will persist into the
evening hours.  The flurries should end after midnight as the upper
level disturbance moves into the Great Lakes. Once the disturbance
moves into the Great Lakes, clouds should then slowly clear across
the southwest half of the area around sunrise Friday.

On Friday, high pressure from the Plains will move into the area.
The high will allow a partial break up of the remaining clouds
across the northeast half of the area. However, due to a warmer
layer of air aloft, the possibility does exist that the clouds will
remain across the area on Friday.

Temperatures on Friday will average well below normal.

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 243 PM CST Thu Dec 8 2016

The main forecast issues in the long term period are an active
weather pattern characterized by a couple of rounds of winter
weather over the weekend, followed by very cold conditions next week.

Friday night: Expect cold and dry conditions with a surface ridge
across the area, and lows in the single digits to teens.

Saturday/Saturday night: Confidence is increasing regarding this
period and the potential for accumulating snow, especially north of
Interstate 80. The latest WRF is a northern outlier, with good
agreement regarding the initial WAA snow area among the
ECMWF/GFS/GEM. A blend of model QPF and snow ratios of 17:1 yields a
band of 3 to 5 inches of snow north of Highway 30, with a dusting to
a couple of inches along the I-80 corridor. With the total QPF on
the conservative side, and indications of significant forcing in the
dendritic zone, would not be surprised at all to see a small band of
6+ inches. 48 hours out, confidence is not high enough to go with a
watch headline at this time. We will be issuing an updated web
headline at www.weather.gov/dvn along with an updated Hazardous
Weather Outlook. Late Saturday night into early Sunday, there is
some potential for some freezing drizzle as we lose ice introduction
aloft. For now, have left out of forecast but this will need
attention with later shifts as it could compound travel hazards.

Sunday/Sunday night: Overall, synoptic models are in better
agreement today than recent days in developing a second system that
will have the potential for a more widespread snowfall across the
forecast area. The 08/12z GFS/GEM are the stronger solutions
compared to the ECMWF. The operational GFS compares very favorably
to the ensemble mean through the period. The parallel GFS run from
08/00z also lends support for a stronger solution and a broad swath
of moderate to even heavy snow. So, in general, am favoring the more
bullish models right now, but confidence in specific snow
amounts/location/timing remains low.

Monday/Tuesday: The second storm will be exiting Monday morning,
followed by a strong front and cold air surge Monday night into
Tuesday. Snow showers on Tuesday in the cold air would be a typical
scenario. Readings in the single digits above and below zero Tuesday
night, combined with a northwest wind, will result in sub-zero wind
chill values, potentially reaching advisory criteria in the far
north.

Wednesday/Thursday: Very cold conditions will persist, with advisory
criteria wind chills again possible near Highway 20 Wednesday night.
The ECMWF is advertising another significant storm on Thursday,
while the GFS is dry. Have maintained a dry forecast for now, as
plenty of additional run to run changes are expected over the coming
days.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
ISSUED AT 534 PM CST Thu Dec 8 2016

Stratus with MVFR cigs generally 2-3kft agl along with flurries
and a few pockets of light snow showers will persist this evening.
Some clearing and improvement to VFR conditions will be possible
late tonight and Friday, especially at CID and BRL, with subsidence
in wake of departing shortwave. However, early peak of 00z DVN
raob reveals a decent inversion just below 850 mb thus confidence
is low on erosion. As a result, I have opted to remain pessimistic
on any clearing trends for now. W/NW winds will persist through the
TAF cycle and slacken a bit to around 10-15 kts with occasional gusts
around 20 kts possible.

&&

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

$$

SYNOPSIS...08
SHORT TERM...08
LONG TERM...RP Kinney
AVIATION...McClure



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