Area Forecast Discussion
Issued by NWS Rapid City, SD

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522
FXUS63 KUNR 140911
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
211 AM MST Thu Dec 14 2017

.DISCUSSION...(Today Through Wednesday)
Issued at 208 AM MST Thu Dec 14 2017

Initial shortwave is moving over the Rockies and through the Four
Corners region, while the secondary upper wave is approaching the
CWA from the north. Skies across the CWA are mostly cloudy, and
some bands of snow are moving through parts of western SD. At the
surface, winds are northwesterly around 10-20 kts, and
temperatures are in the upper 20s and 30s.

Upper wave will slide through the northern plains this morning,
bringing gusty winds, light snow, and cooler air. Pressure rises,
CAA, and 850 mb winds are not as strong as they were in previous
days, but forecast soundings are indicating the potential for some
strong winds mixing down. Still expecting 20 to 35 mph winds, with
gusts to 50 mph from northwestern into west central SD. Will expand
Wind Advisory into a few more zones. Froude number shows good
upslope enhancement of snow through 18Z, before it gradually
decreases in the afternoon. Another 1 to 4 inches of snow will be
possible for the northern Hills, mainly in the morning hours. Parts
of south central SD could see an inch or two of snow, but other
areas will receive less than an inch. Gusty winds may create some
patchy blowing snow at times. Highs today will be mainly in the 30s,
with 20s in the Black Hills.

Upper ridge will shift over the central states on Friday, as a
trough pushes into the western CONUS. Temperatures will warm into
the 50s. Under partly cloudy skies, westerly winds will be around 10
to 20 mph.

The upper trough will begin crossing the Rockies Friday night into
Saturday, and chances for precip will increase. Light snow will
spread over the CWA through Saturday night, with accumulations
around an inch or less. Colder air will also accompany this trough.
Highs both days will be in the 30s to lower 40s, with lows in the
20s.

Mild and mostly dry weather is expected for the beginning of next
week, as an upper ridge moves over the region. Both the GFS and
ECMWF are showing a trough digging into the western CONUS towards
the end of next week, which could bring much colder weather to the
area for next weekend.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Thursday Night)
Issued At 1013 PM MST Wed Dec 13 2017

Some light snow will spread across northeast Wyoming and western
South Dakota tonight...with snow ending from west to east Thursday
morning into Thursday afternoon. MVFR/local IFR conditions
expected with the snow. Gusty northwest winds will continue into
Thursday afternoon.

&&

.FIRE WEATHER...
Issued At 208 AM MST Thu Dec 14 2017

As temperatures warm into the 50s Friday, relative
humidity will drop to 20 to 30 percent. Westerly winds will be
breezy, gusting above 25 mph at times. Current forecast does not
warrant headlines, but if min RH values drop into the teens,
critical fire weather conditions may result.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until noon MST today for SDZ024.

     Wind Advisory until 3 PM MST this afternoon for SDZ001-002-
     012>014-026-030>032-043-072>074.

WY...Winter Weather Advisory until noon MST today for WYZ057.

&&

$$

DISCUSSION...Pojorlie
AVIATION...7
FIRE WEATHER...Pojorlie



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