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FXUS63 KDVN 132345

Area Forecast Discussion
National Weather Service Quad Cities IA IL
545 PM CST Fri Dec 13 2019


Issued at 256 PM CST Fri Dec 13 2019

Stratus and fog behind the weak cold front that moved through the
area early this morning has taken most of the day to dissipate. 
Where skies cleared earliest, temperatures at mid afternoon have 
reached the upper 40s to around 50 over west central Illinois, 
while east central Iowa was still in the upper 20s and lower 30s 
under the last of the stratus and higher cloud cover moving in 
from the west. These higher clouds were associated with a 
shortwave over central Iowa that was producing a small area of 
light freezing rain/drizzle and snow over central Iowa. This will 
be in the initial concern as it moves through late this afternoon.
Surface analysis showed a reinforcing cold front setting up over 
the northern plains that will be pulled southeast through the 
local area tonight by a shortwave in the cyclonic northwest upper
level flow over Nebraska.


.SHORT TERM...(This Evening through Saturday)
ISSUED AT 256 PM CST Fri Dec 13 2019

The initial concern is the potential for wintry precipitation late 
this afternoon and overnight. Much colder air and brisk northwest 
winds then follow for Saturday behind tonight's cold front.
Based on the dry layer seen on area soundings this morning above the 
surface inversion, and lack of precipitation on surface reports, the 
initial area of reflectivity moving into eastern Iowa is likely 
virga. Further west, a general north to south axis of shrinking 
returns was producing light freezing drizzle and freezing rain. This 
will reach eastern Iowa, likely in a continued weakening mode late 
this afternoon into early evening and will have low chance pops for 
freezing drizzle central and freezing drizzle or snow north with 
little potential for any accumulation or significant impacts. 

Later tonight, the upper level shortwave and developing weak 
surface low over Nebraska passes to our south, pulling a cold 
front through eastern Iowa, northeast Missouri and northwest 
Illinois by morning. The lingering low level moisture and weak low
level convergent flow along and ahead of this feature may produce
another round of light freezing drizzle, based on the favorable 
soundings showing dry mid levels and a lack of mid level lift in
model time/height plots. Fog will also be possible and have added
patchy fog wording over eastern Iowa into northwest Illinois for 
late tonight. Will keep patchy freezing drizzle wording with low 
confidence for any appreciable or impact-producing accumulations.
Model consensus timing of the front would send temperatures into 
the teens northwest to upper 20s in the far southeast by 12Z 

The back edge of any freezing drizzle may continue for a few hours 
Saturday morning. Otherwise, cold air advection and brisk northwest 
winds ahead of high pressure building into the northern plains will 
result in a much colder day for most of the area. Temperatures will 
rise only a few degrees despite a general clearing trend to 
afternoon higher in the 20s northwest to around 30 southeast. 

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 256 PM CST Fri Dec 13 2019

Focus in the extended is with the Sunday/Monday snow event. Beyond 
that, the extended period is rather quiet. 

Key messages:

1) Periods of light snow are now possible from Sunday afternoon 
through much of the daytime hours Monday; ending Monday 

2) Confidence remains low on the finer details, but several inches 
of accumulation are possible for parts of SE Iowa, NE Missouri, and 
west central IL with lower amounts to the north and west.

Surface high pressure will be over the area early Sunday. Meanwhile, 
a trough and developing low pressure area will be emerging from 
eastern Colorado and NE New Mexico. The low is currently forecast to 
track east across Oklahoma and into Arkansas by Monday morning with 
an inverted trough extending northward into the Missouri River 
Valley. It is then expected to zip northeast up the Ohio River 
Valley into Pennsylvania by Tuesday morning.  This track means more 
snow for the southeast portions of our CWA.  The system has speed up 
and migrated northward quite a bit from prior forecast runs, thus 
the onset is now Sunday afternoon across areas south of I-80. With 
model run variations in timing and placement, confidence in 
forecasted snowfall amounts and location are low to say the least. 
However, there is increasing confidence that areas southeast of a 
line from Fairfield, IA to Princeton, IL may see Winter Weather 
Advisory criteria being met over a 24 to 36 hour time frame.  A good 
aspect with this event is that wind should not be much of an issue 
with wind speeds generally under 10 mph. Changes (possibly big ones) 
to the forecast are likely over the next few days, so be sure to 
check back for the latest updates on this system. 

High pressure will dominate much of the remainder of next week 
resulting in dry conditions Tuesday through Friday with a good deal 
of sunshine. Temperatures will remain below normal through 
Wednesday, but highs Thursday and Friday are expected to rise well 
into the 30s and possibly even lower 40s.


.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
ISSUED AT 537 PM CST Fri Dec 13 2019

Variable winds with generally VFR mid/high clouds, and areas of 
MVFR visibility in light fog will begin the TAF period. By late 
evening and overnight winds will increase from the northwest and 
usher in stratus with IFR to lower MVFR ceilings. Ceilings will 
likely remain MVFR for much of Saturday, with increasing VFR
potential over the last 6 hours of the TAF. Winds will be
sustained at or above 10 kts on Saturday and periodically gust 
up to 20 kts. 




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