Area Forecast Discussion


346 
FXUS63 KDVN 110539
AFDDVN
Area Forecast Discussion
National Weather Service Quad Cities IA IL
1139 PM CST Sun Dec 10 2017
...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 06Z TAFS through 06Z Monday Night)
ISSUED AT 1135 PM CST Sun Dec 10 2017
A few flurries may skirt KDBQ overnight, but with low probability
will not mention in 06z TAF. The main impacts through the TAF
period will be a switch to a strong NW wind through the day, and
continuing into Monday evening. Gusts will be around 30kts or
higher from late afternoon into the evening hours. Expect mainly
MVFR ceilings with light snow most favored during the afternoon at
KDBQ.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...Uttech
AVIATION...RP Kinney