Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 241135
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
435 AM MST Tue Jan 24 2017

.SHORT TERM...(Today Through Wednesday Night)
Issued at 244 AM MST Tue Jan 24 2017

The winter storm has been slow to develop, but heavy snow is
still expected over parts of the region today into tonight,
especially over southwestern into south central South Dakota.
The snow is expected to increase in coverage and intensity around
daybreak this morning.

Latest upper analysis shows a broad trough over the western Conus
with a 150KT jet streak on the southeast side of the upper trough,
over New Mexico and Kansas, and a 125KT jet streak rounding the
base of the upper trough in California. The upper low appears to
be developing near Casper, Wyoming based on the center of rotation
seen on the regional radar mosaic and the sfc low is deepening in
southeastern Colorado due to the influence of the jet streak. The
upper low will track eastward today, moving into central Nebraska
during the early evening and the surface low will track eastward
across Kansas today. The first band of precipitation is currently
moving into the forecast area from the southwest in the region of
strongest WAA and moisture advection aloft. Expect the snow to to
increase in coverage and intensity aft 12Z this morning as
frontogenesis strengthens. Relatively steep mid-level lapse rates
will support a period of moderate to heavy snowfall rates across
parts of southwestern and south central South Dakota, esp later
this morning. That is where the heaviest snowfall is expected,
with 6-10 inches likely. Some areas could see a foot of snow, esp
from Wanblee to Winner. Snowfall amounts will be lower to the
north and west with adv criteria amounts, except for the northern
Black Hills where some weak upslope enhancement will support
slightly higher totals around warning criteria. Winds will be of
concern on the SD plains, esp east and south of the Black Hills
where blowing and drifting snow is expected. Previously issued
winter weather headlines still look good.

Snow will quickly taper off late this aftn and eve from west to
east, although blowing snow will remain an issue tonight
especially over south central South Dakota. Wednesday will be
cold, with highs only in the 20s. There is a chance of light snow
over the northern Black Hills and the moisture wraps around the
west side of the low pressure system, there is also a chance of
snow esp on Wednesday morning over south central South Dakota
closest to the low pressure system.

.LONG TERM...(Thursday Through Monday)
Issued at 244 AM MST Tue Jan 24 2017

A broad upper level trough will remain across the
eastern half of the US late in the week, with a highly amplified
ridge over the west coast. North-northwest flow aloft will remain
over the Rockies and Plains. Weak disturbances within this flow will
bring clouds and brisk winds at times, along with a few snow
showers. Best chances for snow showers right now look to be Thursday
over the northern Black Hills and late Saturday into Sunday across
western SD. Temps will remain below average Thursday, with a gradual
warmup to near average temperatures over the weekend as ridge slowly
shifts eastward into the Rockies region.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Wednesday Morning)
Issued At 435 AM MST Tue Jan 24 2017

IFR/LIFR conditions will continue across the area today,
with snow continuing to overspread the area from southwest to
northeast this morning. Snow will continue over much of the area
this afternoon, with the exception possibly being over far northwest
SD, then taper off from west to east late today and tonight.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Warning until 11 PM MST this evening for SDZ024.

     Winter Storm Warning until 5 AM MST /6 AM CST/ Wednesday for
     SDZ027-030>032-041>044-046-047-049-073.

     Winter Weather Advisory until 11 PM MST this evening for SDZ029.

     Winter Weather Advisory until 5 AM MST Wednesday for SDZ012>014-
     025-026-028-072-074.

WY...Winter Storm Warning until 11 PM MST this evening for WYZ057.

     Winter Weather Advisory until 11 PM MST this evening for WYZ055-
     056-058.

     Winter Weather Advisory until 5 AM MST Wednesday for WYZ071.

&&

$$

SHORT TERM...10
LONG TERM...26
AVIATION...26


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