Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 202342
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
442 PM MST Mon Nov 20 2017

.DISCUSSION...(This Evening Through Monday)
Issued at 158 PM MST Mon Nov 20 2017

Large upper ridge will remain nearly fixed over the western
conus, with ridge topping impulses bringing very changeable
weather to the region as the area remains on the edge of the
impulse path. Overall, very mild wx can be expected the next 7
days, with bouts of cooler/colder weather behind passing systems.
Clipper system now traversing the Northern Plains, with an
associated thermal ridge and prefrontal trough over the fa. CAA
will ensue quickly late this afternoon far NW as a strong cold
front surges toward the region tonight. Associated LSA and
moisture pocket aloft will interact over the area tonight to
support some rain and snow. Light snow accums are expected over
portions of NE WY and the northern Black Hills, where 1-2 inches
are forecast, highest over the higher elevations of the northern
Black Hills. Precip should be out of the area by sunrise Tues,
with a sfc high expected over the region, bringing clearing skies
and much colder weather. Many places will see high in the 30s
Tuesday, quite the difference from today. WAA will ensue aloft Tue
night, with a fast moving low pressure system expected to allow
good mixing Wed. This will bring another warm, but breezy day to
the area once again Wed. Deeper/stronger low pressure system will
then take aim at the region Thurs, with the region being on the
WAA side of the system Thanksgiving. Westerly flow, decent
insolation, decent mixing, and very warm thermal fields aloft will
allow record to near record temps, on the plains east of the
Black Hills where low 70s are forecast. Another cold front will
move through Thurs night, possibly bringing some light rain to
areas Friday morning. Given mean storm track, the bulk of CAA
looks to stay east of the region, with only a modest cool down
Friday before the the next deeper system and associated upper
trough pushes into the region and WAA ensues once again. This
system may bring another day of record warmth to the region Monday
with 60s and 70s possible once again if low level flow veers
westerly. A pattern change looks more likely next week as a deeper
trough progresses across the western CONUS and supports a strong
low pressure system on the plains, bringing snow accums, wind, and
cold to a portion of the plains at some point later next week.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening)
Issued At 442 PM MST Mon Nov 20 2017

VFR conditions will continue across the area through the early
overnight hours before conditions deteriorate. CIGS will lower to
MVFR across northeastern WY/northwestern SD by 03-05z as virga
moistens low levels. MVFR VSBYS are likely after 06z at GCC and
surrounding locations as snow begins to reach the surface. IFR
CIGS and VSBYS are likely across higher elevations overnight.
Currently have a few hours of MVFR CIGS at RAP, though it is
possible that dry downslope winds may maintain VFR CIGS. Will
monitor this potential as the night goes on.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION...JC
AVIATION...Sherburn


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