Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 042342
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
542 PM CST Mon Dec 4 2017

...00Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 245 PM CST Mon Dec 4 2017

An approaching cool front is now into central Iowa with a broken
line of showers and non-severe storms. Trends support front to
pass rapidly by 8 PM with south winds of 20 to 30+ mph becoming
west to northwest by mid evening. Light precipitation amounts with
low to very low risk of severe storms suggested. Temperatures are
in the lower to mid 60s at 2 PM with much colder temperatures noted
to arrive by late evening behind front. Below to well below normal
temperatures on tap the rest of the week with little or no snow
chances.

&&

.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 245 PM CST Mon Dec 4 2017

Short term forecast confidence assessment...fair to poor or average
to below average. Main risk is severe risk the next 3 to 5 hours with
trends suggesting a diminishing risk (if any) will need to monitoring
next few hours as low instability and veering surface winds
unfavorable for any severe.

Tonight...broken line of showers and storms should pass east by 10 PM
with clearing skies most areas. Any rain totals should be below a quarter
inch with most locations a tenth of an inch and possibly less. Temperatures
to fall into the lower 20s to around 30F by sunrise with gusty northwest
winds of 20 to 30+ mph with isolated gusts to around 35 mph.

Tuesday...mostly sunny and cold and windy with temperatures staying
in the 30s with gusty northwest winds of 20 to 35 mph and some gusts
around 40 mph possible. Wind chills will be in the teens to lower 20s
for coldest day so far this winter season.

.LONG TERM...(Tuesday Night through next Monday)
ISSUED AT 245 PM CST Mon Dec 4 2017

Tuesday night and Wednesday...Latest run 12z models varying on
handling of a weak clipper embedded in cold northwest flow this
period. The GFS is the most bullish with the forming of a closed sfc
low dropping acrs the southwestern third of the DVN CWA from 06z-12z
Wed morning, placing up to a half inch of snow by 12z-14z Wed just
to the north of it generally along and just south of the I80
corridor. The 12z NAm dries up anything to maybe just some flurries,
and the new ECMWF produces a few tenths of an inch/dusting along and
west of Iowa City and Cedar Rapids by Wed morning, and dries it up
to flurries after that. For now will go with a strip of flurries in
these areas from late Tue night into Wed morning, but could see a
few areas getting light measurable snow accums of a tenth or two
from southwest of Cedar Rapids, through the Quad Cities and point
southeast. After that system clears Wed morning, rest of the day
blustery and cold in the upper 20s to low 30s in much of the area.
Northwest winds of 15 to 25 MPH and gusts up to 35 MPH. The winds
decrease some overnight but still maintain enough to produce low
single digit to around zero wind chills in the north and northwest
by early Thu morning.

Thursday and Friday...Cold day under passing lobe of sfc ridging
Thu, highs probably staying in the 20s most areas. Thu night may be
one of the coldest nights of the week with quick temp drop/crash
expected just after dark, but increasing cirrus and signs of at
least late night southwest sfc return flow may limit true cold
potential and produce non-diurnal temp trend by early Fri morning.
If the clouds and winds delayed, some chance of single digit lows in
a few locations. The latest run medium range models then suggest the
next clipper in line for Friday and Friday night, but again vary on
strength and moisture availability to work with. The 12z ECMWF is
less phases and separates two energy centers that pass mainly west
and northeast of the local fcst area, and just produces a half inch
or less of snow accum from late Fri afternoon and into the evening.
The more phased 12z GFS rippling along llvl baroclinicity produces
at least 1-3 inches acrs much of the area starting late Fri
afternoon, and lasting through midnight before shuttling off to the
southeast. These amounts utilizing higher LSR`s of 15:1 to 20:1
taking into account cold vertical profiles. For now will cover
Friday with moderate to high CHC POPs.

Saturday through next Monday...Cold post-frontal and blustery day
again on Sat with highs held in the 20s in most areas(especially if
there is some fresh snow cover of an inch or two), then longer range
indications of another vigorous wave digging into eastern CONUS L/W
trof actually inducing some moderating return flow acrs the region
late Sat night and Sunday...Sunday highs a a result may be well up
in the 30s and even low 40s in the south. Then the models diverge
some into early next week, but the general sign is for ongoing
northwest flow to be active and usher down clippers almost every day
for snow chances/snow swaths of at least light snow accumulation
potentail, acrs portions of the upper Midwest into GRT LKS Mon
through next Wed. Long range indications also suggest a chunk of
real cold Canadian air possibly could dump down acrs the western GRT
LKS behind one of these waves early to mid next week...the current
GFS says next Wed with -25 to -28c values at H85 MB clipping the
area.    ..12..

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
ISSUED AT 528 PM CST Mon Dec 4 2017

Line of showers and storms will sweep through the terminals vicinity
of Mississippi River over the next hour or so. The strongest
storms will bring wind gust potential to around 40-45 kts. In the
wake of the storms and passage of a cold front WNW winds will
remain strong/gusty at 25-35+ kts, with a period of low clouds and
MVFR cigs 1500-3000ft agl settling into the terminals by mid
evening lingering overnight before decreasing and returning to
VFR conditions toward/around daybreak. Anticipate VFR conditions
then on Tuesday with NW winds 20-30 kts.

&&

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

$$

SYNOPSIS...Nichols
SHORT TERM...Nichols
LONG TERM...12
AVIATION...McClure



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