Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 102341
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
541 PM CST Sun Dec 10 2017

...00Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 338 PM CST Sun Dec 10 2017

Seasonably cool and breezy conditions were found across the region
with another afternoon of post frontal cold advection northwest
winds. At 2 pm, the surface boundary that moved through this
morning reached from SW lower MI to SE MO. Visible satellite
images show a large deck of stratocu in the wrap around cyclonic
low level flow reaching into far eastern IA and northwest IL,
where it is dissipating in place. Temperatures ranged from the
lower 30s northeast to lower and mid 40s in the deeper mixing
across the south and southwest. The next system to affect the area
was evident on satellite water vapor imagery as a tight
circulation along the border between Alberta and Saskatchewan,
embedded in the upper level northwest flow from central Canada
into the central U.S. This feature will push through the local
area Monday, bringing a quick round of light precipitation,
followed by another period of windy conditions Monday night into
early Tuesday.

&&

.SHORT TERM...(This Evening through Monday)
ISSUED AT 338 PM CST Sun Dec 10 2017

Main focus is on the next clipper system to impact the area late
tonight and Monday with possible light snow accumulations.

Tonight: Decreasing winds and initially mostly clear skies will
allow temperatures to drop into the mid to upper 20s by late
evening, then a gradual rise is likely as winds back again to the
south and cloud cover returns. A warm front connected to the
initial surface low moving into central MN will lead to around of
elevated warm air advection and low chances for light snow are
kept mainly north of the highway 20 corridor toward morning. Dry
air will likely keep any measurable snowfall closer to the
surface warm front well north of the forecast area.

Monday: The tightening upper level vort max is shown with good model
agreement diving southeast through eastern IA into northwest IL
at midday. This may produce at least a brief period of strong lift
in the dendritic growth zone from roughly 15z to 20z from east
central IA into the northwest IL north of the I-80 corridor. The
GFS and NAM lack any resulting QPF over the local area with this
feature, likely due to being initially too dry, but the ECMWF,
latest available Canadian, and most convective models suggest at
least a few hundredths of an inch QPF with this feature, which
looks more reasonable given the strong forcing. For now, have
increased our chance pops, which will need to be further bumped up
into at least likely range unless the system changes considerably.
Initially, surface temperatures may be too warm for snow in the
system`s warm sector and thus have rain or rain/snow at the onset,
changing over to snow with dynamic cooling and then ensuing cold
air advection and possible trailing trough following the passing
surface low, shown tracking NW to SE through eastern IA into
northern IL during the day. This may lead to light snow
accumulations, which are kept mainly below a half inch, north of
the the highway 30 corridor.

Overall, forecast confidence is average to low for this system due
to uncertainty in critical thermal fields, amount of mid level
instability, and track of the strong upper level forcing. It
certainly will need to be watched closely for the potential for a
quick burst of measurable snowfall, which at this time would be
possible over far eastern IA into northwest IL Monday afternoon.

.LONG TERM...(Monday Night through Sunday)
ISSUED AT 338 PM CST Sun Dec 10 2017

Overall this extended period looks quiet. Northwest flow aloft will
continue through the upcoming week. However, any ripples in the flow
that traverse E Iowa/NW Illinois will be weak. By Friday into next
weekend, the 500mb flow is forecast to become zonal, signaling a
warm up through next weekend.

Monday Night

Pressure gradient increases behind departing clipper system, and
coupled with efficient boundary layer mixing/cold air advection, NW
winds are forecast to gust 30-35 mph. Temps will bottom out in the
mid/upper 10s north to the lower 20s far south.

Tuesday through Thursday

The coldest day of next week will be Tuesday when 850mb temps tumble
into the -10 C to -14 C range - forecast highs are in the lower 20s
NE to lower 30s SW. For Wednesday through Thursday night, models
have backed off on precip chances. There could be a few brief
periods of light rain or snow showers, but the majority of this
period will be dry across our CWA.

Friday On...

Temps are forecast to moderate as 500mb heights over the Midwest
rise and the ridge over Western North American begins to flatten.
The consensus model blend has above normal temps through next
weekend. It also appears the dry weather will continue as the jet
and associated storm track shifts well north toward the Northern
Plains and Upper Great Lakes. Uttech

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
ISSUED AT 530 PM CST Sun Dec 10 2017

MVFR cigs has spread into Wisconsin and northeast Iowa just
clipping the DBQ terminal at 00z TAF issuance. These clouds will
lift to VFR by early Monday morning. A fast moving upper level
storm system will move through the region on Monday bringing a
wind shift and perhaps some flurries/light snow Monday afternoon.
Have included a PROB30 group only at DBQ at this time as there is
higher confidence there, but may need to add at other terminals
in later cycles. An MVFR deck will likely be seen behind the
passing system Monday afternoon and evening and have included this
likelihood at all terminals.

&&

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

$$

SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...Uttech
AVIATION...Gross



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