Area Forecast Discussion
Issued by NWS Rapid City, SD

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196
FXUS63 KUNR 061813
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1113 AM MST Tue Dec 6 2016

.UPDATE...
Issued at 1112 AM MST Tue Dec 6 2016

Current surface analysis shows strong area of low pressure
centered over far northeast ND, with secondary arctic front
stretching southwest to southwest SD and into northern WY. Upper
level analysis shows the low over northern MN. Fast zonal flow in
place across the southern half of the country, with another
disturbance over the Northern Rockies moving east-southeast. Gusty
northwest winds continue across the Northern Plains, with some
gusts to over 40 mph continuing in our area to the northeast of
the Black Hills. Webcams over Perkins and Ziebach Counties
continue to show some blowing snow, with reduced visibilities at
times, so will extend the winter weather advisory for blowing snow
across these areas through 300 pm today. Winds will gradually
decrease late this afternoon and evening as low moves further away
from the region. Main updates to the forecast this morning were to
extend the advisory, and add patchy blowing snow to a good portion
of the rest of northwest SD where there is some snow cover. Clouds
will increase late today and this evening as the Rockies system
approaches. It still looks like most or all of the snowfall with
this system will stay south and west of the forecast area later
tonight and early Wednesday, but will keep low pops over far
southwest SD and far southern portions of northeast WY.

&&

.SHORT TERM...(Today Through Wednesday Night)
Issued at 306 AM MST Tue Dec 6 2016

Upper level analysis has closed low over eastern ND, with broad
trof across the northwestern and north central CONUS. Skies are
partly to mostly cloudy across the northern Plains with light snow
and blowing snow across northern portions of SD into ND. At the
surface, deep low pressure is located across northwest MN with
arctic high centered over western MT. Tight pressure gradient
between these two features is keeping winds very gusty over
northwestern SD. Temperatures at 3am are mainly in the single
digits and teens. A few locations across northeast WY have dipped
below zero in the past hour.

Arctic air will continue to surge into the area over the next 36
to 48 hrs, with the coldest air aloft pushing in late tonight into
Wednesday morning. Temperatures will not rise much today, with
weak cold air advection still taking place. Some sun will help to
raise temps into the teens to lower 20s across southern SD. But
brisk winds to the northeast of the Black Hills will keep wind
chill values near or below zero during the day. With the gusty
winds, areas of blowing snow will persist across northwest SD
through the morning hours. Have extended the Winter Weather
Advisory for far northwest SD through 11 am this morning. Winds
should decrease just a bit across the area for the afternoon, with
only a few isolated areas still seeing some blowing snow issues.

A weak shortwave will move quickly across the northern Rockies
and into the Central Plains tonight. Majority of models have pcpn
staying south of the forecast area late tonight, but the EC does
have some light qpf clipping far southern portions of northeast WY
and far southwest SD. Lows will be near or below zero in most
areas, with wind chills 10 below to 25 below zero. A wind chill
advisory may be needed for a few areas, especially far northwest
SD.

Coldest core of air settle across the area for Wednesday. Most
locations will struggle into the single digits for highs, with
maybe a few lucky spots topping 10 degrees. Unfortunately,
northwest winds will still be breezy on Wednesday, keeping wind
chill values below zero across the area for the entire day. Clear
and cold conditions will persist into Wednesday night, with lows
below zero and wind chill readings once again, ranging from 10
below to 25 below zero.

.LONG TERM...(Thursday Through Monday)
Issued at 306 AM MST Tue Dec 6 2016

Mainly zonal flow sets up for the extended period, with periodic
waves bringing small chances for snow. The best chance looks to be
late Friday and Saturday. Temps will begin to modify on Friday in
our wrn zones as brunt of arctic air shifts slightly eastward, but
given our close proximity to the arctic boundary it will likely
meander back and forth into our cwfa over the weekend into early
next week. This may create large temp differences at times between
northeast WY and the SD plains.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1042 AM MST Tue Dec 6 2016

Gusty northwest winds will continue on the South Dakota plains
through the period. Mainly VFR conditions will dominate over
northeast Wyoming and southwest South Dakota. Areas MVFR CIGS are
expected across northwest into central South Dakota with local IFR
conditions near the ND border in blowing snow.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until 3 PM MST this afternoon for SDZ002-
     013-014.

WY...None.
&&

$$

Update...26
SHORT TERM...15
LONG TERM...Johnson
AVIATION...JC



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