Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 072131

Area Forecast Discussion
National Weather Service Quad Cities IA IL
331 PM CST Wed Dec 7 2016

Issued at 330 PM CST Wed Dec 7 2016

Upper level trough/steep mid level lapse rates were located in
the upper Midwest producing snow showers in MN and the eastern
Dakotas. To our south, weak warm air advection was spreading a
band of light snow across eastern KS and central MO, aided by a
weak disturbance moving across IA. This area of snow was moving
eastward. In the dvn cwa a veil of cirrus was covering the area.
Cold air advection and brisk northwest winds were keeping temperatures
quite chilly. 3 pm readings were in the 20s to around 30 with wind
chills in the single digits and teens.

Farther north, temperatures were in the single digits and teens
in the northern Plains and across MN and northern WI.


.SHORT TERM...(This Evening through Thursday)
ISSUED AT 330 PM CST Wed Dec 7 2016

Forecast focus on cold temperatures and flurries.

Tonight: Weak disturbance will push east of the cwa this evening
with the cirrus shield thinning and shifting east of the cwa
overnight. In the meantime, sensible weather guidance indicates
low stratus gradually spreading across the cwa from north to south
as very cold air aloft drops into the area. Late tonight 850 mb
temperatures fall to the -12 to -14c range. This will allow for
lows tonight mainly in the teens. A west to northwest wind of 10
to 20 mph, with ocnl gusts to 25 mph, will drop wind chills to 5 below
to 5 above.

Thursday: Upper level trough/steep mid level lapse rates will
swing across the cwa, especially in the afternoon. Low stratus
should linger most of the day and scattered flurries are expected,
mainly along and north of Interstate 80. Forecast soundings show
the column has limited/shallow moisture and there is weak forcing
at best for much more than mentioning flurries. West to northwest
winds will be brisk with some gusts to 30 mph. 850 mb temperatures
lower even more, to -16c so expect highs only in the lower 20s at
most locations. Wind chills should remain in the single digits for
most of the day.

.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 330 PM CST Wed Dec 7 2016

Thursday Night through Friday...

Cyclonic flow aloft weakens becoming more zonal with time. Closer to
the sfc, 850mb ridge axis slowly approaches from the west as
attendant warm air advection ramps up. Main story is this will be a
dry -- but cold -- period. The coldest daytime highs of the season
so far are forecast - upper teens to mid 20s. 850mb temps are
progged near -14 C and 1000-500mb thicknesses are forecast to rise
from sub-516 dam to 522 dam by late Friday.

Wind Chills:  The greatest sensible weather impact is going to be
the min overnight/early morning wind chills near 0 F.

Friday Night...

Although mid-level warm air advection/isentropic lift is forecast to
overspread E Iowa/NW Illinois, low-levels will remain dry. And for
that reason, low-end POPs have been removed. This is also when the
850mb ridge axis slides overhead.

Saturday and Sunday...

Accumulating snow is likely across portions of the forecast area. A
shortwave is likely to impact the Midwest this weekend. There is
aloft of uncertainty with respect to location and timing of this
system. Stay tuned to future updates as a lot can change over the
next day or two.

Model discrepancies:

The GFS/GFS ensemble mean/Canadian are cold enough for mainly snow
Saturday into Sunday Morning. The ECMWF is the outlier being nearly
18 hours slower and a bit warmer, nosing the 850mb 0 C isotherm up
into the southern CWA. Outside of the ECMWF, the model suite
suggests a system largely driven by thermal advection and
frontogenetical circulations with a relatively weak sfc low. If this
scenario occurs, the potential band of higher snow totals would
probably be fairly narrow and is favored across the north.

The ECMWF has more intra-model run-to-run inconsistencies the past
few days than the GFS/Canadian and offers a significantly different
storm evolution. It develops a classic looking cyclone, mainly on
Sunday, that strengthens along the low-level baroclinic zone as it
rides to the NE through the Lower Great Lakes. If this scenario
plays out, we could expect more uniform snow amounts and stronger
winds on the back side leading to blowing/drifting. Current forecast
is weighted toward the GFS/GFS ensemble mean/Canadian/NAM.

Monday through Wednesday...

Temps trend even colder with a brief arctic air intrusion likely
with periodic chances for light snow. Areas with snow cover will
easily have highs in the teens, possibly single digits. Current
model blend forecast lows are not below zero. However, with dry
arctic air in place, the setup is there for temps to drop below
zero. The models have flipped since yesterday. The ECMWF is now
colder with the arctic blast than the GFS, dropping 850mb temps as
cold as -24 C across the forecast area. Would not put a lot of weight
on this solution until the run-to-run variability settles down.


.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
ISSUED AT 1136 AM CST Wed Dec 7 2016

VFR conds this afternoon and evening with storm system`s well to
our north and south. Eventually, late tonight and into Thursday an
area of low stratus, ocnl MVFR cigs, will spread southward into
most of the TAF sites. Northwest to west winds around 15 knots
with gusts to 25 knots through most of the period.




LONG TERM...Uttech
AVIATION...Haase is the U.S. government's official web portal to all federal, state and local government web resources and services.