Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 030044
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
644 PM CST Fri Dec 2 2016

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 312 PM CST Fri Dec 2 2016

Broad upper level troughing/steep lapse rates were still spreading
an extensive area of low stratus across much of our region. In the
meantime, high pressure ridge extended from the mid Mississippi
Valley to the Deep South and this is where plenty of sunshine was
occurring. In the DVN cwa, only our far northeast MO counties were
seeing some sunshine, closer to this ridge.

Temperatures ranged from the mid 30s to lower 40s in the cwa to
the 40s and 50s farther south under the ridge.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 312 PM CST Fri Dec 2 2016

Forecast focus on cloud and temperature trends.

Tonight: With extensive low stratus this afternoon over much of
the cwa, and abundant moisture in the low levels, we expect these
clouds to remain stubborn overnight. Can`t rule out some patchy
drizzle/freezing drizzle/sprinkles or flurries with the low stratus
but not confident at this time to add in the grids. Will pass concerns
to the next shifts but not expecting any travel issues.

Due to the extensive cloud cover have raised minimum temperatures
(from previous forecast) into the lower 30s over most of the cwa.
However, there are exceptions to this 1) our far northeast MO counties
where partly cloudy skies will prevail, and 2) in our far nw cwa where
a pocket of -10c 850 temperatures pushes into that area out of MN.
In those two areas lows will drop into the mid to upper 20s.

Saturday: Looking at the mean RH decreasing in the low levels on
time height sections this suggests the stratus should break up
allowing for some sunshine. However, forecast soundings indicate
mid/high level moisture (clouds) will be streaming from southwest
to northeast over the cwa, especially in the afternoon. This will
be due to a long wave trough pushing eastward into the Plains. Low
pressure will also begin to develop in south Texas as an upper level
low/mid level speed max dives southward along Baja California. The
bottom line is skies should be mostly cloudy for much of the day.
Temperatures will be similar to the past couple of days, with highs
in the mid 30s to lower 40s.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 312 PM CST Fri Dec 2 2016

An unsettled winter weather pattern dominates the extended forecast.
Confidence is increasing for 1) the weekend system producing the
season`s first widespread snowfall, then 2), much colder
temperatures developing mid to late next week. The potential for a
significant winter storm later in the week has waned considerably,
at least for now, based on the consensus of the 12z model runs.

Saturday night into Sunday, the merging of energy currently moving
onshore into southern BC and the northern stream shortwave in the
existing trough over the central rockies is progged to transition
eastward over the local area. The resulting surface trough and
moderate to strong mid level lift is shown in good model agreement
from the 12z model runs interacting with moisture return from the
Gulf of Mexico to produce a swath of .3 to .4 QPF across eastern IA
into NW IL Saturday night through Sunday afternoon. The challenge
will be how much of this falls as snow and how much accumulation
occurs on initially warm ground conditions and rising temperatures
Sunday.

Forcing develops around 06z Saturday night into the west, then is
strongest overhead in advance of the upper level shortwave around
12z to 16z Sunday morning. Thermal profiles support the
precipitation beginning as snow, possibly mixed with rain in the far
south. With a low level southeasterly feed of dry air into the
system, and web bulb cooling, most of the area should have light to
moderate snow Sunday morning, followed by a increasing south winds
and warm air advection. This may result in a mix, or changeover to
rain, or more likely drizzle on the back edge of the departing lift
Sunday afternoon. With relatively low snow to liquid ratios and the
wet nature of the snow,have gone with snow totals in a range of
roughly 2 to nearly 3 inches north of the highway 34 corridor and
half to 1 inch south into northeast MO and west central IL.

Another upper level system follows Monday night into Tuesday, but
with the strongest lift focusing further north and more limited
moisture, the only model to generate any precipitation over the
forecast area this model run is the Canadian. This shows a possible
round of light snow with the associated cold frontal passage Tuesday
afternoon and evening. For now, only slight chance pops are
maintained. The main impact will be the onset of much colder
temperatures that will be the main story from mid to late week. A
developing upper level trough over the central then eastern U.S.
will pull down the coldest air of the season so far, limiting
temperatures to the teens and 20s. The Canadian and ECMWF depict a
round of snow with an impulse in the cyclonic flow Wed night into
Thu, which is handled with chance pops Wed into Wed night. For now,
the much more significant winter storm well advertised in previous
model runs is nearly non-existent, but cannot be totally ruled out
yet as details in the evolution of this pattern is low considering
the energy is well out over the Pacific.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
ISSUED AT 629 PM CST Fri Dec 2 2016

MVFR to low VFR ceilings will persist through the TAF period with
a light west to northwest wind under 10 kts. Any precipitation is
expected to hold off until later Saturday night.

&&

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

$$

SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Sheets
AVIATION...RP Kinney



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