Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 071120

Area Forecast Discussion
National Weather Service Sioux Falls SD
520 AM CST Wed Dec 7 2016

.SHORT TERM...(Today and Tonight)
Issued at 302 AM CST Wed Dec 7 2016

Breezy west to northwest winds will continue today as modest cold
air advection aids in drawing momentum from aloft down to the
surface. Could also see periods of flurries throughout the day as
very efficient atmosphere remains in place in the lowest several
thousand feet.  Do not expect any accumulation, but may see some
temporary reduced visibilities.

High temperatures today will be just a few degrees above seasonal
lows.  That is indicative of the strength of this airmass given the
lack of snowcover across the area.

Low temperatures tonight will fall back into the single digits. With
the brisk wind, wind chills will remain in the single digits and
teens below zero.

.LONG TERM...(Thursday through Tuesday)
Issued at 302 AM CST Wed Dec 7 2016

A cold forecast remains in the medium and extended portions of the
forecast. The primary forecast concerns and areas where forecast
modifications include:

1. Light snow or flurries risk on Friday.
2. Higher probability of accumulating and impactful snow on Saturday.
3. Increasing likelihood of even colder air next week.

Thursday: The primary focus on Thursday will be with reinforcing
stratus moving into the area early in the day. Soundings already
showing stratus layer residing with a low DGZ, and a very subtle
shortwave embedded within the synoptic upper trough may provide
enough lift to focus scattered snow showers or flurries for a
majority of the day.

Friday: As upper troughing slides eastward into the Northeast,
surface high pressure will drift across the Northern Plains. In
response to a slightly increasing mid-level ridge axis and very
modest shortwave lifting northeast by midday. Models showing
potential for a narrow band of light snow to lift northeast during
the day.  Model QPF generally not very representative and may be
biased by a dry sub-cloud layer, but at a minimum have coordinated a
jump in PoPs with only minor accumulations (less than 0.5").

Saturday: The most striking change to the forecast is within the
Saturday and Saturday night timeframe. Models coming into agreement
that a progressive NW Pacific shortwave will race through the
Northern Plains on Saturday. GFS is the deepest of the solns, with
the ECMWF/GEM more broad in their depiction of the wave as it moves
through. That said, there is an even split in distribution of GEFS
members between the two camps.  With a cold air regime in place,
these progressive waves can become trouble, given their potential
for initial warm advection snows, followed by the stronger synoptic
lifting. For now, cautiously splitting the differences in the solns,
which bring light snows to the area late Friday night, with
increasing warm advection snow Saturday morning. Should the now
deeper GFS/GEM/NAM ideas verify and the upper jet become more
involved, there is potential for this to become a more prolific snow
producer. At of this junction in time, snow amounts may fall in the
2 to 5" range.

Sunday-Wednesday: The overall trend continues to point towards
colder than normal temperatures through next week. With fresh snow
on the ground on Sunday, highs may struggle to reach the teens. Deep
upper troughing over North America will keep a persistent flow of
minor shortwaves through the area, with guidance from the ECMWF and
GFS suggesting a bigger arctic surge heading into the area by
Tuesday and Wednesday.  This surge could have the potential to bring
widespread below zero temperatures and single digit highs by the
middle of next week. Something to keep an eye on at least.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 517 AM CST Wed Dec 7 2016

VFR Conditions expected at TAF sites through the period. Gusty
west/Northwest winds will continue through the period. Could see
some flurries develop throughout the day, especially in SW
Minnesota which may result in temporary reductions in visibility.




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