High Wind in South Dakota, December 22 to 23, 2020

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
936 PM CST Tue Dec 22 2020

.UPDATE...
Issued at 933 PM CST Tue Dec 22 2020

No major changes made to the forecast this evening. Beginning to
see light precipitation now move into the west river counties, and
things still look on track for the precipitation to spread across
the area overnight through early to mid afternoon on Wednesday. No
changes made to winter weather headlines at this time.

&&

.SHORT TERM...(This Evening through Wednesday Night)
Issued at 349 PM CST Tue Dec 22 2020

Much above normal temperatures late this afternoon will be followed
by high winds, snow, blizzard conditions, arctic air, and
falling wind chills.

Temperatures late this afternoon were in the 50s and 60s across the
region in the warm sector of an intense (990mb) surface low pressure
area in northwest SD/southwest ND. Behind this low pressure area
was arctic air, along with good pressure rises. The models all
agree well on the timing, track, and strength of this surface low
pressure area moving across our region through Wednesday night.
They also agree pretty well on the QPF and snowfall amounts.
Therefore for tonight, expect the leading edge of mixed
precipitation of rain and snow to transition quickly over to snow
as it moves quickly from west to east through Wednesday morning.
One issue tonight will be the warm ground from the warm weather
today and the quick fall in temperatures behind the cold front.
Therefore, look for some initial snow melt followed by a quick
refreeze and possible ice on the roads. With the CAA and winds
gusting to over 60 knots at the top of the mixed layer, high winds
across the entire CWA look like a good bet. Also, with good
deformation/trowal snowfall behind the strong upper level low
pressure area on Wednesday, widespread snowfall of 1 to maybe 4
inches is expected.

The main issue in this forecast, especially west of the James
Valley, is will there be enough snowfall accumulating in
combination with the high winds to create widespread blowing
snow/possible blizzard conditions. Therefore, at this time with
the latest increase in snowfall amounts and high winds expected
across the CWA, made many upgrades to the winter weather
products. With the rapid cooling, snowfall, and high winds,
upgraded to High Wind Warning and Winter Weather Advisory from
the James River Valley and west through Wednesday afternoon and
went with a blizzard warning east of the James Valley into west
central Minnesota into Wednesday evening. The snow and blowing
snow will end quickly through Wednesday afternoon and evening with
skies clearing and winds decreasing. Wind chills will fall
quickly Wednesday night to 10 below to 30 below zero.

.LONG TERM...(Thursday through Tuesday)
Issued at 349 PM CST Tue Dec 22 2020

The period begins Thursday morning with a cold air mass in place,
especially so east of the Missouri River, thanks to strong CAA on
the backside of a strong low pressure system. Sfc high pressure
builds in by the afternoon, but until then, northwesterly winds (20+
mph gusts across northeastern SD and west central MN) will
exacerbate the cold. Wind chill advisory-level wind chills are most
possible across west central Minnesota Thursday morning. Single
digit high temperatures are also forecast across and east of the
Coteau Thursday.

While potent, this cold spell will be brief. As the sfc high slides
to the east Thursday night, a return flow ushers in much milder air
for Friday/Christmas. Southwesterly flow at 925mb Friday morning may
lead to some enhanced downslope winds on the leeward side of the
Prairie Coteau as well. Impacts in terms of blowing snow are
uncertain however, due to temperature and the existence of blowable
snow. By Friday afternoon, sunny skies and WAA increases
temperatures into the 30s east of the Missouri River and 40s along
and west of it.

The upper-level ridge that helped build warmer air for Friday
becomes quickly replaced by an incoming shortwave Saturday, and
below normal temperatures return by Sunday, though only slightly
below normal. In terms of precipitation, the area looks to stay
largely dry through the weekend, with only very low PoPs on Sunday,
associated with the shortwave, at this time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 532 PM CST Tue Dec 22 2020

Terminals KABR,KATY,KPIR,KMBG

VFR conditions will prevail across the area through around 06Z. A
storm system will then track across the area, bringing
precipitation and very strong winds to the region late tonight
into the day Wednesday. The precipitation may begin as rain across
the central part of the state late tonight, but will then
transition to snow and remain snow until it exits the region.
Periods of IFR/MVFR vsbys in snow and blowing snow will occur
beginning west of the Missouri River around 06Z, then quickly
spreading eastward over the remainder of the area by sunrise
Wednesday. Strong northwest winds of 30 to 45 knots will accompany
the snow. The gusty winds will continue through the day, but look
for the snow to end and vsbys to improve some during the mid to
late afternoon hours.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...High Wind Warning until 6 PM CST /5 PM MST/ Wednesday for
     SDZ003>006-009-010-015>018-033>037-045-048-051.

     Winter Weather Advisory until 6 PM CST /5 PM MST/ Wednesday for
     SDZ003>006-009-010-015>018-033>037-045-048-051.

     Blizzard Warning from 3 AM to 8 PM CST Wednesday for SDZ007-008-
     011-019>023.

MN...Blizzard Warning from 3 AM to 8 PM CST Wednesday for MNZ039-046.

&&

UPDATE...Parkin
SHORT TERM...Mohr
LONG TERM...KF
AVIATION...Parkin

Hazardous Weather Outlook...UPDATED
National Weather Service Aberdeen SD
303 PM CST Tue Dec 22 2020

SDZ003>006-009-010-015>018-033>037-045-048-051-232115-
Corson-Campbell-McPherson-Brown-Walworth-Edmunds-Dewey-Potter-Faulk-
Spink-Stanley-Sully-Hughes-Hyde-Hand-Jones-Lyman-Buffalo-
303 PM CST Tue Dec 22 2020 /203 PM MST Tue Dec 22 2020/

This Hazardous Weather Outlook is for central South Dakota, north
central South Dakota and northeast South Dakota.

.DAY ONE...Tonight.

High winds and snow are expected to develop after midnight. Winds
gusting to over 60 mph could bring some blowing snow and lower
visibility.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

High winds and snow will continue into Wednesday with 1 to 3 inches
of snowfall expected. There will also be areas of blowing snow with
low visibilities at times. Temperatures will plummet along with wind
chills into Wednesday night.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be requested. Weather spotters are encouraged
to submit reports to the National Weather Service in Aberdeen. The
public can submit reports on our web page, Facebook page, or our
Twitter feed.

MNZ039-046-SDZ007-008-011-019>023-232115-
Traverse-Big Stone-Marshall-Roberts-Day-Clark-Codington-Grant-Hamlin-
Deuel-
303 PM CST Tue Dec 22 2020

This Hazardous Weather Outlook is for west central Minnesota and
northeast South Dakota.

.DAY ONE...Tonight.

High winds and snow are expected to develop late tonight. Winds
gusting to over 60 mph will bring blowing snow and lower visibility
with blizzard conditions possible by Wednesday morning.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Snowfall of 2 to 4 inches along with winds gusting to over 60 mph
will result in blizzard conditions through Wednesday. Temperatures
will plummet along with wind chills into Wednesday night.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be requested. Weather spotters are encouraged
to submit reports to the National Weather Service in Aberdeen. The
public can submit reports on our web page, Facebook page, or our
Twitter feed.

Mohr