Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 072339
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
539 PM CST Thu Dec 7 2017

...00z AVIATION UPDATE...

.SYNOPSIS...
Issued at 330 PM CST Thu Dec 7 2017

Steep north-northwesterlies continue acrs much of the northern
Rockies into the mid MS RVR Valley, west of northeastern Hudson Bay
upper low complex, while dry warm ridge extended up the west coast.
Long wave trof long fetch shear axis was currently extending from
northwest Mexico, though Maine and the southeastern Canadian coast.
This pattern to generally maintain into next week, opening the
region to occasional clippers, weak waves and re-enforcing cold
dumps.

&&

.SHORT TERM...(This Evening through Friday)
ISSUED AT 330 PM CST Thu Dec 7 2017

Tonight...main challenge will be how cold to go. Dry sfc layer, low
sfc DPTs and ongoing cold airmass overhead support a colder than
guidance lows night. But passing sfc ridge and llvl pressure
gradient progged to keep sfc winds going at least from 4-7 KTs
overnight, with a backing to the southwest component. These mixing
winds and the potentail of cirrus thickening from the northwest as
the night progresses(or even a deck of stratocu out of MN late), make
for a reason for not going with a complete temp potentail bottom-
out. But still see a quick temp drop off this evening after sunset
and may get close to projected 12 hour lows by 10 PM or Midnight.
For now will still side with cooler of guidance lows, but if sfc
winds decouple even more and there is a delay on cirrus thickening
overhead, some potential of single digits in a few locations
tonight. In this northwest flow regime, any stratocu deck that can
make it into the area and lower to at least 4-5K FT AGL will be
capable of producing at least a few flurries. Some chance of this
into the far north/at least to HWY 20 just before sunrise.

Friday...Better chance for a stratocu deck with embedded flurries
making it into at least the northern third to half of the DVN CWA
during the morning as a lead vort lobe ripples in overhead. Southwest
llvl flow will increase to to 10-20 MPH with warm air advection
processes also supporting the chance for at least some spotty light
precip breaking out in spots. After the lobe passes, may be a
temporary lull in precip during the afternoon except for the far
north. WAA southwest flow may make for highs in the mid 30s acrs
much of the area, and would be even warmer in spots if it were not
for the expected partly to mostly cloudy skies much of the day. More
afternoon sunshine than expected will make for a temp buts of the
mild side by at least a few degrees...some areas pushing the upper
30s.   ..12..

.LONG TERM...(Friday Night through next Thursday)
ISSUED AT 330 PM CST Thu Dec 7 2017

The highlights of the long term period are snow chances with the
passage of several clipper type systems, and near to below normal
temperatures.

Friday night-Sunday: A clipper system will drop south out of
Manitoba, not a favorable track for significant impacts to the
forecast area. Still, there will likely be a nice area of -15C omega
and a favorable PV anomaly skirting the north. These factors, and a
decent model consensus support raising pops to categorical far
northeast, with an area of light accumulations, mainly northeast of
a line from Independence and Davenport, to Princeton. The Freeport
area will likely see the higher amounts, around an inch, possibly up
to 2. Little or no accumulation is expected to the southwest of the
line. A northwest wind will increase early Saturday morning, gusting
near 30 mph, and could produce some shallow blowing and drifting of
the newly fallen snow. Wind chills will also dip into the single
digits and teens into Saturday morning. Gusty winds and very chilly
conditions will persist through the day Saturday, with highs only in
the 20s. Saturday night will be quite cold, with moderating
temperatures into the 30s and 40s Sunday.

Looking ahead, there may be a couple of additional clippers
impacting the area early next week, and possibly late week as well.
However, timing and placement among the various synoptic models
continues to vary considerably, and there is low confidence in snow
for any particular period. As a result, will continue to stay with
the model blend pops, which favor Sunday night into Monday, and
again Tuesday/Tuesday night. This will likely change, so the basic
message is expect some additional periods of light snow/flurries
with the exact timing to be determined.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
ISSUED AT 529 PM CST Thu Dec 7 2017

VFR conditions anticipated through the TAF cycle with increasing
clouds overnight and Friday, and ceilings gradually lowering into
4-8kft agl range by Friday PM. A few flurries will also be
possible on Friday. There is a low chance of MVFR ceilings of
1500-2500 ft agl developing into DBQ and CID Friday PM, as some
guidance suggests lower clouds dropping out of MN into northeast
IA. These clouds are associated with a clipper system, which is
likely to spread light snow across WI on Friday and IL and far
eastern IA later Friday evening into the predawn hours on Saturday.

&&

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

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...RP Kinney
AVIATION...McClure



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