Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 100522
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1022 PM MST Tue Jan 9 2018

.DISCUSSION...(This Evening Through Tuesday)
Issued at 338 PM MST Tue Jan 9 2018

Current surface analysis shows low pressure over northern MT,
with warm front stretching east-southeast through northern
portions of the Northern Plains. Weak low pressure is also located
over far northeast WY, with a trough extending southeast into
southern SD. Upper level analysis shows weak ridge axis now east
of the area, with southwest flow developing ahead of an upper low
over southern CA. A northern stream shortwave trough is located
over the Pacific NW. Skies are variably cloudy across the area
with mild temperatures, mostly in the 40s and lower 50s.
Southwesterly winds are gusty across parts of northeast WY. Winds
are south to southeast in most other areas.

Hopefully you have enjoyed the mild and pleasant weather of the last
several days because unsettled and much colder weather is going to
return Wednesday and persist through the end of the week as general
troughing over the west moves across the Central US. Two systems are
expected to impact the area, with the first one tomorrow into
tomorrow night expected to be more potent than the second one coming
Thursday night into Friday.

For tonight, skies will start off partly cloudy, becoming mostly
cloudy by morning. Temperatures will remain mild ahead of cold front
to the northwest, lows in the upper 20s and 30s. The cold front will
move into the forecast area from the northwest during the early
morning, then quickly pass south and east of the forecast area by
early afternoon. Highs during the day will be during the morning
hours, 30s and lower 40s, with temps falling in the afternoon.

Most of the pcpn will be post-frontal as the northern stream
shortwave moves across the Northern Plains during the day and into
Wednesday night. Pcpn could briefly start as a little light rain in
some areas, but should quickly change over to snow as the colder air
rushes in. Snow will be heaviest across far northeast WY into
northwest SD during the late morning and afternoon and across parts
of southwest into south central SD during the later afternoon and
evening. Snowfall totals will mostly be in the 1 to 3 inch range,
with some higher amounts likely across far northeast WY, the
northern Black Hills and far northwest SD. Parts of far south
central SD could also see some locally higher amounts as the impacts
of weakening low moving across the southern Rockies and plains could
clip the area Wednesday night. Winds will be the other issue as 15
to 30 mph winds develop across much of the area, with some gusts to
around 40 mph likely across the northwest and west central SD plains
during the afternoon and early evening. Areas of blowing snow are
expected to develop during the afternoon with reduced visibilities.
Have left headlines generally as is, except for adding northern
Campbell and Crook counties in WY to the advisory. Snow will taper
off from west to east during the evening and into the overnight
hours, with winds gradually diminishing as well. Lows by Thursday
morning will mostly be in the 5 below to 5 above zero range with
wind chills 10 below to 25 below.

Temps are expected to be below average through much of the forecast
period, with the coldest temps to the north and east of the Black
Hills, where highs are expected to be in the single digits and teens
most days. Across northeast WY and the Black Hills, highs will be
milder, mostly in the 20s and lower 30s. The next shortwave system
will move across the area in west-northwest flow later Thursday
night into Friday. Some light snow is looking increasing likely with
the system, with an inch or so of accumulation in spots, possibly a
couple of inches over the northern Black Hills. After that,
relatively quiet wx is expected. However, an upper low will
redevelop over the Hudson Bay region and south central Canada later
this weekend into early next week, keeping cold conditions across
the Northern Plains. A brief warmup is possible on Sunday before a
reinforcing shot of colder air arrives for the early part of next
week. We could also see some light snow or flurries late in the
weekend into the early part of next week as the colder air moves
in.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1019 PM MST Tue Jan 9 2018

VFR conditions expected through 12z Wednesday. A fast moving cold
front and storm system will bring gusty northwest winds along
with a band of snow from northwest to southeast later Wednesday
morning through early Wednesday evening. Conditions will rapidly
deteriorate due to snow/blowing snow with widespread IFR and areas
LIFR conditions expected.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from 8 AM Wednesday to 2 AM MST Thursday
     for SDZ001-002-012>014-024-025.

     Winter Weather Advisory from 5 PM MST /6 PM CST/ Wednesday to 5
     AM MST /6 AM CST/ Thursday for SDZ044-046-047-049.

     Winter Weather Advisory from noon Wednesday to 2 AM MST Thursday
     for SDZ026-030>032-042-043-072>074.

WY...Winter Weather Advisory from 8 AM Wednesday to 2 AM MST Thursday
     for WYZ057-071.

     Winter Weather Advisory from 8 AM to 11 PM MST Wednesday for
     WYZ054-056.

&&

$$

DISCUSSION...26
AVIATION...Helgeson



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