Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 070525

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1025 PM MST Tue Dec 6 2016

Issued at 640 PM MST Tue Dec 6 2016

01z surface analysis had 1044mb high over western Canada nosing
deep into the northern and central Plains. Weak cold air
advection continues. Shortwave entering southeast WY will brush
against CWA later tonight with small chances for -SN in the south,
but main effect will be an increase in cloud cover.

Latest guidance and collaboration with CYS indicates wind chills
will reach -25F across all of northeast WY and parts of southwest
SD Wednesday morning. Thus, will expand wind chill advisory to
account. BLSN ending across the north, so will drop those
headlines on-time.


.SHORT TERM...(This Evening Through Wednesday Night)
Issued at 322 PM MST Tue Dec 6 2016

Current surface analysis shows strong area of low pressure
centered over northwest MN, with secondary arctic front stretching
southwest to northwest Neb and WY. Upper level analysis shows the
low now 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 toward the Central Plains.
Gusty northwest winds continue to the northeast of the Black
Hills, though winds are starting to slowly decrease. Webcams still
showing some blowing snow and reduced visibilities in portions of
Perkins and Ziebach counties, so will extend the advisory to 700
pm for these areas. Temps range from the single digits over
northwest SD to the lower 20s over far southern SD, with near or
below zero wind chills across northern portions of the cwa.

Arctic air will continue to push into the area through Wednesday,
with well below average temperatures continuing through the short
term period. Lows late tonight will generally be a few degrees
either side of zero in most areas, with colder spots over snow
covered areas of northeast Wyoming, the Black Hills, and northwest
SD. Clouds will help keep temps up a bit later tonight over far
southern SD. Winds will gradually decrease, but still remain breezy
over far northwest SD overnight. Wind chill values over far
northeast WY, the northern and central Black Hills, and much of
northwest SD will drop to 20 below to 30 below zero later tonight
into Wednesday morning. Have issued a wind chill advisory for these
areas late this evening through Noon Wednesday. Shortwave system to
the west will move into the Central Plains later tonight and
Wednesday morning. Still looks like most or all of pcpn will stay
south of the forecast area, but will keep some low pops across far
southern portions of northeast WY and far southwest SD late tonight.

Highs on Wednesday will be in the single digits and lower teens,
mildest over far southern SD. Brisk winds will develop again over
the SD plains, but not as strong as today. This will keep wind
chills near or below zero through the day. Lows will be near or
below zero again Wednesday night with very cold wind chills. Wind
chill advisories may be needed again for portions of the area.

.LONG TERM...(Thursday Through Tuesday)
Issued at 322 PM MST Tue Dec 6 2016

Mean troughing over northern NOAM will remain in place through
the period with the region on the northern edge of the jet
stream/storm track. This will support very cold conds as a
modified arctic airmass remains in place. Active shortwave storm
track will support chances for snow once again across the area
this weekend, as a pac origin system traverses fast westerly flow.
The main belt of snow associated with this system will be over or
near the fa, with the latest model runs trending more south into
the fa. This could support a quick 1-3 inches of snow Sat, esp
given high snow ratios are under very cold profiles. Otherwise,
the GFS, CMC, and ECMWF have started to converge toward early next
week, supporting another arctic outbreak stronger than the current
version. This would bring sig colder air into much of the fa
toward the middle of next week with highs below zero possible at
many locations esp over the NE third. The bulk of CAA looks to
remain north of the fa, but still cold nonetheless.


.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1022 PM MST Tue Dec 6 2016

Gusty northwest winds will continue on the South Dakota plains
through the period. Mainly VFR conditions will dominate
southwestern South Dakota. Areas MVFR CIGS are expected across
northwest South Dakota and northeast Wyoming through Wednesday
afternoon with improvement Wednesday night.


SD...Wind Chill Advisory until noon MST Wednesday for SDZ001-002-012-

WY...Wind Chill Advisory until noon MST Wednesday for WYZ054>058-071.



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