Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 210533
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1033 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 06Z TAFS Through 06Z Tuesday Night)
Issued At 1033 PM MST Mon Nov 20 2017

VFR conditions continue across TAF sites for now. However, IFR
CIGS and/or VSBYS are ongoing across northeast WY and the northern
Black Hills and should continue through most of the overnight.
Expect GCC to fall to MVFR by 06z as lower CIGS upstream approach.
Should also begin to see sufficient moistening for snow to reach
the ground around this time. Not currently expecting IFR
CIGS/VSBYS at GCC, but it is plausible that IFR conditions could
briefly occur through 10z. Snow should end by 12z as mid and upper
levels dry rapidly, but low CIGS will continue into Tuesday
afternoon. Western SD (outside of the Black Hills) may temporarily
drop to MVFR CIGS/VSBYS with light rain/snow showers tonight, but
conditions should improve to VFR for most of Tuesday.

&&

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

$$

DISCUSSION...JC
AVIATION...Sherburn



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