Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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852
FXUS63 KDVN 060552
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1152 PM CST Mon Dec 5 2016

...AVIATION UPDATE...

.UPDATE...
Issued at 834 PM CST Mon Dec 5 2016

Southeast winds have ramped up to sustained speeds of 15 to
nearly 20 mph over much of the area this evening thanks to the
deepening cyclone over far west central MN. A shallow, cool and
moist low level airmass capped by strong warm advection southerly
flow and a much drier air 950 mb to 800 mb, as seen on KDVN 00z
sounding, was resulting in areas of mostly MVFR fog. The exception
was DBQ, where there was some local terrain enhancement, resulting
in a rapid drop to one quarter mile over the past hour.

With winds likely to diminish as the cold front over western Iowa
approaches overnight, conditions will become more favorable for
widespread dense fog. Will likely need a dense fog advisory later
tonight, likely lasting until the mid morning frontal passage
clears things out.

Have updated the forecast for current fog coverage and overnight
wording for the onset of widespread fog and at least patchy dense
fog. Winds were also increased this evening. Much like last night,
temperatures will likely vary little until the fropa, varying only
2 to 3 degrees around 30 to 35.

&&

.SYNOPSIS...
Issued at 300 PM CST Mon Dec 5 2016

What a difference snow cover makes! Across the dvn cwa low stratus,
fog and temperatures in the 30s due to snow melt moisture trapped
below an inversion at 900 mb. In western IA and into KS with bare
ground and sunshine readings were in the 50s!

Skies were clearing in portions of our far sw counties but expect
this to fill back in with stratus by late afternoon after peak heating.

&&

.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 300 PM CST Mon Dec 5 2016

Forecast focus on clouds, fog and possible light pcpn mix followed
by a cold front on Tuesday.

Tonight: With snow melt into this evening low stratus and areas
of fog (advection) on southerly winds will continue through tonight.
The question will be how widespread and dense the fog may get overnight
so will let the next shifts monitor the trends and any need for a
dense fog advisory. Some sensible weather guidance suggest dense
fog others do not. A trough digging southeast into the Midwest
later tonight, and deepening cyclone in northern MN, will bring a
band of forcing into our far nw cwa. However, moisture is limited
so will continue slight pops for a mixture of light precipitation.
Minimum temperatures should range from the upper 20s to lower 30s.

Tuesday: This forcing will lift quickly northeast away from the
cwa early in the morning followed by a cold front pushing southeast
across the cwa. Brisk west to northwest winds and gradually falling
temperatures can be expected, especially in the afternoon. Highs
will be in the 30s before beginning to fall. We will mention areas
of fog in the morning ahead of the front. However, with the colder/drier
airmass and brisk winds with the passage of the front, any low stratus
and fog should scour out rather quickly.

.LONG TERM...(Tuesday Night through Monday)
ISSUED AT 300 PM CST Mon Dec 5 2016

Tuesday Night: Cold air advection with westerly sfc winds and a
period of clear skies will allow temps to fall into the 20s and 10s.
Early morning wind chills on Wednesday are forecast as cold as the
single digits roughly in the counties along and north of I-80 with
teens further south.

Wednesday and Wednesday Night: 850mb temps continue to fall dropping
to -10 C by the afternoon. Expecting an increase in cloud cover from
the early morning on. Current forecast highs are in the mid 20s
north to lower 30s south. For precipitation, have a slight chance
for light snow or flurries (15-20%) across the southern tier or two
of counties. GFS/NAM are completely dry. If ECMWF/Canadian trend
drier, will be able to remove chances. For now, looks like a dusting
or nothing. Overnight lows from model consensus are in the teens and
min wind chills are near zero.

Thursday and Friday: Cold to round out the work week in the upper
teens to mid 20s (850mb temps -12 C to -14 C and 1000-500mb
thicknesses between 510-516 dam); coldest overnight to morning wind
chills are forecast near zero. Cyclonic mid-level flow, steep low-
level lapse rates, and with vorticity maxima rotating through, could
have periods of flurries or light snow showers. However, forecast is
dry right now because threat for measurable precipitation, 0.01
inches or more, is low.

Friday Night: Deep warm air advection/isentropic lift could initiate
a band of light snow in the Upper Midwest. Of course, model
consistencies exist at this lead time. POPs are low in the 20-30%
range, favoring our north half. Overall, moisture is limited in
the models for this period.

Saturday and Sunday: Another shortwave may impact the Midwest. The
GFS/GFS ensemble/Canadian are cold enough for mainly snow, the ECMWF
is the outlier being warmer and further north with the precip. Stay
tuned to future updates as a lot can change with respect to
strength/timing/impacts. Model blend temps warm into the 30s CWA-
wide by Sunday. Uttech

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
ISSUED AT 1151 PM CST Mon Dec 5 2016

...Updated to add overnight light precipitation potential...

Brisk southeast winds from 10 to 20 knots have delayed the
anticipated onset of dense fog, but as winds diminish ahead of an
approaching cold front, the fog is expected to thicken toward
morning. Will maintain the transition to VLIFR, due to very low
visibilities and ceilings of a few hundred feet, roughly from 08z
to 12z. A cold front will likely bring a rapid improvement to at
least MVFR and then VFR conditions around mid morning, along with
winds veering westerly and becoming gusty. A band of a mix of
light rain and light snow along the front over central Iowa is
expected to weaken as it moves east-northeast, but could still
impact CID and DBQ toward morning. This has not been included in
the forecasts for now, as if it does hold together it should be
very light and short-lived. Later Tuesday morning, confidence in
the the transition to much improved conditions is low and later
forecasts will likely be able to be more precise. VFR conditions
should then follow Tuesday afternoon and evening.

&&

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

$$

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



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