Winter Storm Warning 6, NWS Aberdeen, SD

Area Forecast Discussion
National Weather Service Aberdeen SD
1249 PM CDT Tue Mar 12 2019

.UPDATE...
Issued at 1014 AM CDT Tue Mar 12 2019

Wind speeds have diminished some across the far northeastern part
of the area, with webcams indicating improving conditions as far
as blowing snow goes. Therefore, have cancelled the Winter Weather
Advisory for that area. Still some areas of fog lingering across
mainly the northwestern part of the CWA. Otherwise, no major
changes made to the forecast this morning.

&&

.SHORT TERM...(Today through Wednesday Afternoon)
Issued at 334 AM CDT Tue Mar 12 2019

It's the lull before the storm. For today conditions overall should
be relatively tranquil as a mild airmass continues to advect into
the region (ie...H85 temps above +5C). Meanwhile, aloft a s/w is
pressing northeast across the state this morning per water vapor
loop. Overall the atmosphere is quite dry across the region this
morning and expected to remain that way so not expecting much if
anything from that wave. Morning sat pix also continue to indicate
roving areas of fog and low clouds, mainly west of the James valley.
Most of the fog should dissipate this morning with daytime heating.
Another batch of waa clouds could move into especially the eastern
cwa today from the south. Temperatures will be relatively mild,
topping out mainly in the 30s today, with perhaps some 40s over
south central sections of the state.

For tonight aviation progs/grids indicate plenty of fog spreading or
developing across the forecast area, and that seems logical based
on the melting that should ensue today. Low tonight should be
relatively mild and in the 20s, with a few teens for north central
South Dakota. Wednesday is the day the southwest CONUS upper low
starts tracking north/ne toward the region. Pcpn is expected to
gradually spread into the cwa from the south during the day. Types
will probably start off as freezing rain or rain and then transition
to snow during the day over the western CWA. Some fairly hefty pcpn
amounts are possible Wednesday into Wednesday night, likely leading
to some localized flood issues at that time. Icing may also become a
problem, especially from the James valley east toward Minnesota.
Temperatures are expected to top out in the low to mid 30s for most
areas.

.LONG TERM...(Wednesday Evening through Monday)
Issued at 334 AM CDT Tue Mar 12 2019

A very dynamic storm system will impact the region during the early
portion of the long term, or Wednesday night into Thursday night.

The period begins with a powerful surface low pressure system
passing southeast of South Dakota. Based on the NAEFS return
interval, the surface low is considered outside the climate average,
or extremely rare. It should come as no surprise winds on the
backside of the storm system are also rare, occurring once every 5
to 10 years, or outside the climate normal in locations. These
strong winds, along with moderate to heavy snowfall will produce
dangerous conditions west of the James River Valley Wednesday night
into Thursday afternoon. Precipitation type in eastern South Dakota
and western Minnesota is a completely different challenge. A few
models are showing warm air aloft with rain possible at the surface
very early Wednesday night. As colder air moves in, the pcpn type
should change over to freezing rain. Ice accumulation of a tenth of
an inch could be possible. A slower transition over to snow will
mean higher ice accumulation. Of course a faster transition would
equal more snow.

Precipitation should gradually diminish from west to east across the
state on Thursday with dry conditions likely by Thursday night.
Winds will slowly diminish from west to east Thursday through Friday
morning. Once falling snow ends, the threat for widespread blowing
snow should end shortly thereafter.

An uneventful long term is expected beyond the midweek storm system.
Dry conditions, but with below average temperatures are expected.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 1246 PM CDT Tue Mar 12 2019

VFR conditions will persist longest at KABR/KPIR - with KMBG stuck
under some fog for the next few hours. KATY will see the worst
conditions this time period, with low stratus and reduced
visibility in fog. Precipitation will be moving up into the area
near the close of this TAF period as well, most likely only
reaching KPIR/KATY in the last hour or so.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Watch from Wednesday morning through late Thursday
     night for SDZ003>011-015>023-033>037-045-048-051.

MN...Winter Storm Watch from Wednesday morning through late Thursday
     night for MNZ039-046.

&&

UPDATE...Parkin
SHORT TERM...TDK
LONG TERM...SD
AVIATION...Connelly

Hazardous Weather Outlook
National Weather Service Aberdeen SD
442 AM CDT Tue Mar 12 2019

MNZ039-046-SDZ003>011-015>023-033>037-045-048-051-130945-
Traverse-Big Stone-Corson-Campbell-McPherson-Brown-Marshall-Roberts-
Walworth-Edmunds-Day-Dewey-Potter-Faulk-Spink-Clark-Codington-Grant-
Hamlin-Deuel-Stanley-Sully-Hughes-Hyde-Hand-Jones-Lyman-Buffalo-
442 AM CDT Tue Mar 12 2019 /342 AM MDT Tue Mar 12 2019/

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

.DAY ONE...Today and tonight.

Areas of fog are expected overnight.

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

A significant storm will bring rain, freezing rain, heavy snow and
strong winds to the region for Wednesday and Thursday. Blizzard
conditions are possible over the James and Missouri river valleys
Wednesday night and Thursday. Heavy rain is possible over the Big
Sioux valley Wednesday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.