Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 152321

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
421 PM MST Wed Nov 15 2017

.DISCUSSION...(This Evening Through Wednesday)
Issued at 305 PM MST Wed Nov 15 2017

Current surface analysis shows frontal boundary nearly
stationary across the area, from far northeast WY to south central
SD, with high pressure over south central Canada. Upper level
analysis shows trough over the Great Lakes region, with ridging over
the Rockies, and a low off the Pacific NW coast. Skies are partly
cloudy to mostly sunny across the area as some high clouds spill
over the ridge. Temps range from the mid 30s across far northwest SD
to near 50 over far southwest SD. Winds are mostly northerly to the
north of the boundary, southerly over northeast WY to southwest SD.

Mainly dry weather will continue through at least the first half of
next week as relatively dry west-northwest flow aloft persists.
Temperatures will continue the roller-coaster trend of late, with
warmer air returning tomorrow, then the next cold front dropping
temps back to near average levels for Friday and Saturday. Highs
Thursday will be in the mid 50s to upper 60s, with gusty
southwesterly winds from northeast WY to far southern SD.

The main chances for pcpn during the period will come late Thursday
night and Friday as a shortwave passes quickly through the area
behind the cold front. The better chances for pcpn still look to be
from far northeast WY to northwest SD and the Black Hills. Pcpn
should mostly start as rain and then convert over to snow in many
areas Friday morning as colder air pushes in. A mix is then expected
into the afternoon before ending in the evening over eastern areas.
Not expecting much in the way of pcpn amounts in most areas, but a
decent band of frontogenesis is expected behind the front early
Friday and could produce at least a band of light accumulating snow
somewhere from far northeast WY to northwest SD.

Sunday and Monday both look dry and mild as weak ridge to the west
slides over the region. Medium range models diverge significantly
toward midweek and Thanksgiving. Latest GFS is an extreme outlier
compared to the EC and Canadian models. EC and GEM keep at least a
weak ridging pattern in place over the Rockies and high Plains, with
milder and mainly dry weather persisting through the holiday. 12Z
GFS brings a strong trough southward out of Canada midweek, with
very cold and unsettled conditions in place by Thanksgiving day.
Previous runs of the GFS were more in line with the other models, so
will generally disregard this latest run at this point.


.AVIATION...(For the 00Z TAFS Through 00Z Thursday Evening)
Issued At 421 PM MST Wed Nov 15 2017

VFR conditions are expected through the period. As southwesterly
flow increases tonight, some low-level wind shear will be possible
across parts of the area.


Issued At 305 PM MST Wed Nov 15 2017

Gusty southwesterly winds are expected Thursday, especially
across northeast WY and far southern SD, with minimum relative
humidities in the 20s creating elevated fire danger in these
areas. Colder and moister air settles in Thursday night into
Friday as a cold front moves through.




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