Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 010947

Area Forecast Discussion
National Weather Service Quad Cities IA IL
347 AM CST Thu Dec 1 2016

Issued at 323 AM CST Thu Dec 1 2016

Stacked low was crossing Ontario early this morning. Our region
and much of the north central CONUS resides in seasonably cold,
deep cyclonic flow with widespread low clouds, and some flurries
and drizzle/very light rain over portions of the Upper Midwest
into the Great lakes.


.SHORT TERM...(Today and Tonight)
ISSUED AT 323 AM CST Thu Dec 1 2016

Cloudy skies and seasonable temperatures will be a mainstay of the
forecast, as we remain entrenched in deep cyclonic flow attendant
to the weakening low shifting slowly east from Ontario through
Quebec. Lift from a weak impulse shifting southeast from MN will
support some flurries or patchy drizzle mainly north of Hwy 30 this
morning. Beyond this morning the lack of any coherent forcing
precludes any precipitation mention, with only weak channeled
vorticity progged tonight ahead of an impulse over SD. While can`t
completely rule out some very spotty extremely light precip in
cyclonic flow/caa the prospects appear to low for inclusion. Should
anything occur drizzle would be suggested with sounding analysis and
rh progs showing drying out aloft and loss of ice nucleation in the
-10c to -18c layer. However, low cloud bases may be even a bit high
for this to occur.

Persistent clouds will put the clamps on diurnal ranges limiting to
only around 5 degrees or so. Thus, highs today on the cold side of
guidance or roughly similar to Wednesday with a general range 35-40.
Lows tonight favor above the warm side of guidance due to the clouds
and only settling into the range of 30-35.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 323 AM CST Thu Dec 1 2016

Quiet and dry conditions will be seen Friday through Saturday as
high pressure moves through the Midwest. Temperatures will be close
to normal. Attention then turns to the approaching storm system.

A very dry atmosphere initially over the area at sunset Saturday
will result in a dry Saturday evening. As the atmosphere saturates
from top down precipitation will break out after midnight. Various
techniques indicate the precipitation will be a rain/snow mix that
may change to all snow. The warm ground should prevent any
accumulation but a dusting might occur on elevated surfaces. As warm
air surges into the area, the mix across the south third will change
over to all rain prior to sunrise Sunday.

Sunday on...

Sunday morning all rain should be seen across the south third of the
area with a rain/snow mix elsewhere. A very minor dusting of
accumulation on elevated surfaces might occur. The northern two
thirds of the area will see a change over to all rain during the
morning. Sunday afternoon the rain will end from southwest to
northeast across the area. Temperatures should be near to slightly
above normal.

The model consensus has dry conditions Sunday night and Monday as
high pressure quickly moves through the Midwest. Attention then
turns to the next storm systems.

As mentioned yesterday, the hemispheric flow pattern is extremely
energetic. When this situation occurs, the models are very sensitive
to initial conditions and will show considerable changes from run to

Most models are showing a weak disturbance moving through the area
Monday night/Tuesday. The previous 1-2 model runs had a more
substantial system. The overall hemispheric flow pattern would
support the bulk of the energy with a storm system staying well
south of the area. Given the expected lack of run to run continuity
of the individual models, the model consensus of chance pops Monday
night and slight chance to chance pops Tuesday look reasonable. A
mix of rain and snow that may change over to all snow Tuesday night
looks reasonable. Again, the warm ground should result in little if
any snow accumulation.

A much more interesting weather situation is setting up for the
Tuesday night/Wednesday time frame.

The overall atmospheric energy supports a significant storm system
developing. However, this same energy is resulting in the models
having very poor run to run continuity. The expected storm system
development is being either delayed or non-existent with each model
run or its position and track is changing by several hundred miles
with each model run.

The key is what will occur with the weak system Monday
night/Tuesday. Again, the models vary on their respective solutions
and from run to run. Some solutions are bringing in colder air with
the weak system that would then be in place for the stronger system.
Other solutions keep the colder air across western Iowa and
Minnesota. If the cold air is in place for the stronger system, then
the Boehmke rule will be satisfied and the precipitation type would
have a better chance of being snow. If the cold air stays well to
the north and west, then precipitation could end up being rain or a
rain/snow mix.

Right now the model consensus has slight chance pops Tuesday night
with chance pops on Wednesday.


.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
ISSUED AT 1148 PM CST Wed Nov 30 2016

Expect lingering -shsn at all sites but KBRL during the early
morning. IFR to MVFR ceilings will persist through the TAF period,
with a westerly breeze precluding any light fog.




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