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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
315 am CST Thursday Dec 18 2014

Short term...(today and tonight)
issued at 314 am CST Thursday Dec 18 2014

As upper level system approaches from the southwest...high pressure
pulls off to the east. System today will mainly affect areas to our
south...but there may be enough lift across portions of southern County Warning Area
so have continued with mention of 20 probability of precipitation for mainly light snow.
Right now I feel we will mainly see clouds as models saturate the
middle levels but never get much lower so as earlier shift
mentioned...any precipitation will have to overcome the dry layer to make
it to the surface. Continue to believe as well that precipitation will be
in the form of light snow versus drizzle.

Models continue to indicate that cloud cover is not going to go away
after the snow ends. Right now...I would not surprised to see much
of the County Warning Area east of Mitchell to be stratused in for period of time as
we approach the weekend. Low sun angle and weak flow or mixing
should allow the stratus to self perpetuating.



Long term...(friday through wednesday)
issued at 314 am CST Thursday Dec 18 2014

The main issue for Friday and Saturday look to be the persistence of
stratus lingering across the area through the period. This in
response to a moist southerly 925 mb flow streaming into the region
under warming temperatures aloft. All models are pointing toward
this solution...so kept a mostly cloudy scenario...moreso in our
east...for both days. Cannot completely rule out some drizzle with
these clouds...though moisture is fairly shallow and lift weak so
did not include at this time. Did introduce some drizzle in our east
on Saturday night however as moisture deepens and lift is enhanced
by a shortwave tracking across the area. Does appear that
temperatures would be cold enough at that point that freezing
drizzle will be a threat. By early on Sunday may be able to get rid
of some of the stratus as the lower level flow becomes more
west/southwesterly behind the exiting wave. Temperatures for Friday
through Sunday will be fairly consistent...although with some subtle
warming through the period as highs go from the lower to middle 30s on
Friday to middle and upper 30s by Sunday. Lows look to be teens and 20s
with warmest readings in the east where the potential for thicker
cloud cover will exist per the above discussion.

Attention then turns to the upper level trough which will dive
southward and deepen over the central Continental U.S. For the beginning of
next week. The European model (ecmwf) continues to deepen the low a little farther to
the south than the GFS...and thus offers a cooler solution...though
both models have plus 0 c temperatures at 850 mb on Sunday
night...at least in our southwest...so included a threat of some
freezing rain through the western Missouri River corridor for that
time period. By Monday both models have thermal profiles
cooling...so it seems that precipitation type would mainly come down
to surface temperatures on that day. With current expected highs in
the middle and upper 30s on Monday included a rain/snow mix for wording
in the forecast. The potential for snow will linger for Monday night
and Tuesday as upper level energy swings around the deepening upper
level low over the upper Mississippi Valley...and thermal profiles
would support all snow at that point. By Wednesday system begins to
pull away with even cooler air being drawn southward behind the
system.



&&

Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1150 PM CST Wednesday Dec 17 2014

Middle level clouds increasing from the west and expect that trend
to continue into the daylight hours of Thursday. May see a little
light snow spread in southern reaches of the area during the
morning and then spread a little furhter north. Dont expect any
visibility restrictions but ceilings could go IFR with the -sn and then
stratus may stick around for a while after the snow ends.



&&

Fsd watches/warnings/advisories...
South Dakota...none.
Minnesota...none.
Iowa...none.
NE...none.
&&

$$

Short term...heitkamp
long term...jm
aviation...heitkamp

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