Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 142340

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
440 PM MST Sun Jan 14 2018

.DISCUSSION...(This Evening Through Sunday)
Issued at 315 PM MST Sun Jan 14 2018

Current surface analysis shows arctic front sliding south across
SD, with warm front east-southeast of the forecast area. Upper
level analysis shows low over southern Hudson Bay, with large
trough covering central and eastern portions of Canada and the US.
A ridge is in place along the west coast. Shortwave energy and
moisture in northwest flow aloft is sliding southeast across
eastern MT, northeast WY, and western SD and interacting with the
front. KUDX radar shows areas of snow across far northeast WY
through a good portion of western SD, with some light rain across
parts of far southwest SD. Northern edge of pcpn is pushing slowly
south across northwest SD. Temps currently range from the upper
teens across far northwest SD to the upper 30s across far
southwest SD. Northwesterly winds are mostly in the 15 to 30 mph
range across the area, with some gusts to near 45 mph across the
northwest and west central SD plains.

Front will continue to track south across the area through the early
evening, with much colder air rushing in behind it. Light snow will
continue across northeast WY, the Black Hills, to southern SD, with
some heavier upslope enhanced snowfall continuing across the
northern Black Hills and Bear Lodge Mts into the early evening.
Still looks like an inch or less of total accumulation across much
of the plains, with 1 to 2 inches across far northeast WY into the
adjacent plains of the northern Black Hills. The northern Black
Hills and Bear Lodge Mts will see 2 to as much as 5 inches of
snow, higher amounts generally across favored higher elevations.
Upper level energy and front will slide south of the area by
midnight, with snow tapering off from north to south southern
portions of the CWA during the evening.

The coldest air will settle in late tonight and Monday morning as
clouds decrease, with lows from zero to around 15 below by Monday
morning, coldest over far northwest SD. Northerly winds of 10 to 15
mph late tonight into Monday will produce wind chills of 10 below to
35 below, lowest to the north and east of the Black Hills. A wind
chill advisory is in effect for much of the SD plains through
Tuesday morning. Conditions will likely improve above advisory level
criteria for a time Monday afternoon, but will drop back by Monday
evening again. Highs on Monday will be mostly in the single digits
and lower teens, with parts of far northwest SD staying below zero.
Clear skies and light winds will allow temps to drop below zero
again Monday night, with some lows in the 20s below likely from
northwest into central SD.

Dry weather is then expected through at least Thursday as ridge over
the west coast moves east through the plains. This will also bring
much warmer weather, especially by Wednesday and Thursday, with
temps above average late week. Southwest flow develops by the end of
the week into next weekend as large scale trough is progged to move
into and across the western US Friday into Saturday. Medium range
models are showing differences with the specifics of the trough as
it moves into the plains over the weekend. Latest GFS and Canadian
split the trough, with the northern stream wave possibly bringing
some light snow. Latest ECMWF is more aggressive with bringing the
main southern system into at least southern portions of the forecast
area and keeping the northern wave north of the region. Will keep
chance pops across a good portion of the area from later Friday into
the weekend, with the better chances across southern SD.
Temperatures will likely drop back to near or slightly below average
levels over the weekend.


.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 440 PM MST Sun Jan 14 2018

MVFR/IFR cigs/vsbys will persist within a band of moderate/heavy
snow moving southwest across the area. Heaviest snowband at the
moment is located from roughly KSPF to KRAP. This activity will
persist at KRAP through approximately 0100-0130z before shifting
southwest of the site. Snow still appears on track to clear the
remainder of our area by 06z, with skies clearing rapidly
thereafter. Some wind gusts 25-30 kt will persist overnight
through Monday afternoon across western SD.


SD...Winter Weather Advisory until 11 PM MST this evening for SDZ024.

     Wind Chill Advisory from 11 PM MST /midnight CST/ this evening
     to 11 AM MST /noon CST/ Tuesday for SDZ001-002-012>014-025-

WY...Winter Weather Advisory until 11 PM MST this evening for WYZ057.

     Wind Chill Advisory from 11 PM this evening to 11 AM MST Tuesday
     for WYZ071.



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