Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 042125
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
325 PM CST Mon Dec 4 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 318 PM CST Mon Dec 4 2017

Well advertised potent surface low and upper level trough will
continue to dig across the northern and central Plains into tonight.
This fast moving system will be a strong punch of colder air and a
band of precipitation. The main precipitation player will be
associated with the deformation band which currently extends from
south central SD into eastern North Dakota. This band will continue
to slide eastward through the evening hours, exiting to our east by
midnight tonight. Frontogenetic forcing ahead of the deformation
band has not really materialized as expected, which had delayed the
onset of precipitation across the forecast area. The cold air
advection and strong winds however remain on track. Winds will
continue to gust to 35 to 45 mph with locally higher gusts to 55 mph
possible through the evening.

With the initial push of precipitation into south central SD and the
highway 14 corridor in SD over the past few hours, we have received
reports of rain freezing on powerlines and causing outages when
combined with the strong winds. With the low and mid levels cooling
rapidly this evening, expect the patchy freezing rain threat in
these areas to quickly switch over to snow. Will add mention of
freezing rain to the winter weather advisory in south central and
east central SD.

High res models such as the HRRR and NAM derivatives indicate the
potential for localized convective enhancement with the stronger
forcing arriving as the band of snow move approaches the I-29
corridor, then into southwest Minnesota. Think that brief heavy snow
will be possible for areas mainly along and north of I-90, however
the progressive nature of this system will limit snowfall amounts
from piling up more than than 2 to 4 inches. Most locations will be
closer to the 1 to 2 inch range, while amounts will generally be an
inch or less in northwest Iowa. With the strong winds and "flash
freeze" type conditions as the temperatures cool rapidly, travel
conditions will be hazardous. Blowing snow and reduced visibilities
will be a huge concern with near blizzard conditions possible during
snowfall. Timing places the snow band in the FSD and SUX areas
during the evening commute. Decided to expand the winter weather
advisory further east into MN and southeast SD, generally following
where an inch or more of snow is possible. Again, amounts are not as
big of a factor in the advisory as the blowing snow and poor
visibility conditions. Elsewhere, the wind advisory remains in
effect for northwest Iowa and northeast NE where the winter weather
advisory is not in effect.

Skies will clear behind the exiting system tonight, with strong
winds only decreasing a small amount overnight. Northwest winds
remain windy into Tuesday, averaging 15 to 30 mph with higher gusts.
Clouds will be on the increase late tonight and Tuesday as a
reinforcing shot of cold air arrives with a trailing wave. Lows
tonight reach the teens with highs in the 20s to near 30 on Tuesday.
with the strong winds, wind chills will drop to near zero or a few
degrees below zero late tonight.


.LONG TERM...(Tuesday night through Monday)
Issued at 318 PM CST Mon Dec 4 2017

With the focus on the ongoing storm system, did not make any
alterations to the blended forecast in the mid and long range.

Pattern remains cold in comparison to the recent weather pattern,
but not extreme, with highs in the 20s and 30s. Northerly upper
level flow pattern stick around through the end of the week, with
a sharp ridge over the west coast and troughing over the Great
Lakes region. Models hint at several weak waves dropping
southward through the northern Plains during the week, however
model timing of these waves remains uncertain. Precipitation
chances remain spotty at best.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1105 AM CST Mon Dec 4 2017

The main concerns are MVFR/IFR to occasional LIFR conditions as
snow and strong winds move into the area, at least for the first
half of the TAF period. An area of snow is already falling over
central South Dakota and moving east across the area by this
afternoon. Strong northwest winds gusting to 40+ knots and
falling snow may lead to reduced visibilities and near-blizzard
conditions at times. Snow will gradually taper off from west to
east through early evening. While winds are expected to diminish
through around midnight, gusts up to 25 knots will be possible
Tuesday morning.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until 8 PM CST this evening for
     SDZ038>040-050-052>070.

     Wind Advisory until midnight CST tonight for SDZ071.

MN...Winter Weather Advisory until 8 PM CST this evening for MNZ071-
     072-080-081-089-097-098.

     Wind Advisory until midnight CST tonight for MNZ090.

IA...Winter Weather Advisory until 8 PM CST this evening for IAZ001.

     Wind Advisory until midnight CST tonight for IAZ002-003-012>014-
     020>022-031-032.

NE...Wind Advisory until midnight CST tonight for NEZ013-014.

&&

$$

SHORT TERM...
LONG TERM...
AVIATION...05



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