Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 112120
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
320 PM CST Mon Dec 11 2017

.SYNOPSIS...
Issued at 320 PM CST Mon Dec 11 2017

A strong upper level shortwave in the northwest flow aloft was
pushing into west central Illinois at mid afternoon. An associated
low pressure clipper system at the surface has pushed through the
forecast area and was over east central Illinois. Precipitation in
the form of rain, snow and some sleet or snow pellets has been over
mainly the northwest half of the forecast area so far today, with a
gradual trend of changing over to snow from the north and northwest.
Deeper mixing along and south of the upper level system, and a
tight surface pressure gradient with strong pressure rises in its
wake was resulting in windy conditions across especially the
south. Southeast Iowa, northeast Missouri and west central
Illinois have had periods of winds from 20 to 30 mph with gusts
over 40 mph, pushing advisory criteria at times.

&&

.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 320 PM CST Mon Dec 11 2017

Strong winds and ending precipitation are the main challenges.
Northwest winds will likely be close to advisory levels this evening
in the tight pressure gradient and enhanced subsidence axis behind
the shortwave. Have kept winds 20 to 30 mph with gusts into the 30s,
but conditions will not be as supportive of the more widespread 40
plus mph gusts experienced earlier with this system. Winds will
then gradually dissipate overnight, remaining in a 15 to 25 mph
range.

The axis of mixed precipitation along the highway 30 corridor and
east central IA at mid afternoon will continue to migrate south-southeast,
rotating around the departing shortwave and in the axis of low
deformation. Convective models and lift in the dendritic growth
zone in the operational models indicate continued weakening of
the precipitation, with some local bursts of large wet flakes as
the system spreads south and southeast late afternoon into early
evening. Any additional measurable amounts will likely be less
than a half inch and before 7 pm. Latest radar trends support the
heaviest amounts along and east of the MS river, north of the Quad
Cities. Have kept scattered flurries going through the evening,
with falling temperatures as cold air advection increases. Have
gone with model trends of decreasing clouds after midnight and
guidance lows around 15 north to around 20 south.

Tuesday, an advancing weak ridge will lead to decreasing northwest
winds. Shallow mixing and the colder incoming airmass should
limit highs close to a range from the mid 20s northeast to mid 30s
southwest.


.LONG TERM...(Tuesday Night through Monday)
ISSUED AT 320 PM CST Mon Dec 11 2017

Overview: Fast northwest flow aloft will allow for a series of
clipper systems to push rapidly southeast across the Midwest.
However, the bulk of the system`s should remain north and east of
the dvn cwa with only minor precipitation amounts expected.

Temperatures will be on a roller-coaster ride with a quick warm-up
ahead of each clipper, followed by colder temperatures behind it,
then warming up again ahead of the next clipper, so you get the idea.
These temperature changes will be almost daily owing to the rapid
movement of each storm system.

Of particular interest is the storm system that tracks from the
central Plains to the Ohio Valley late this weekend. However, low
confidence in the track and potential impact to the dvn cwa, if any.
The ECMWF gradually deepens the cyclone and spreads a swath of
accumulating snow across portions of the dvn cwa Saturday night and
Sunday. However, the GFS/Canadian take the system much farther south
leaving the cwa totally dry. As of now, the grids are heavily
weighted towards the dry GFS. Definitely something to monitor as the
week progresses.

Haase

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
ISSUED AT 1126 AM CST Mon Dec 11 2017

A fast moving low pressure system will spread fast moving rain and
snow showers through the area this afternoon, along with
developing strong surface winds. Precipitation is most likely to
affect CID, DBQ and MLI this afternoon, followed by a period of
low clouds with MVFR ceilings lingering into the evening.
Northwest winds following this system will be sustained at 25 kts
for a few hours with gusts possibly over 35 kts. While not
included in the forecasts, flurries will be possible this evening.
Winds will gradually decrease overnight and forecasts have winds
dropping below 15 kts by Tuesday morning.

&&

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

$$

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



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