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Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota
432 PM MDT Thursday Sep 18 2014

Short term...this evening through Friday night
issued at 222 PM MDT Thursday Sep 18 2014

20z surface analysis had low over central sk with warm front into
western NE...and cold front into eastern Idaho. Shortwave noted on
water vapor over northwest Wyoming...swiftly moving northeast. Lower
60 dew point/S have pooled along warm front creating a good amount of
SBCAPE but thermal ridge building 800-600mb keeping cin rather
high across the plains.

Tonight...shortwave energy whisks into ND pushing cold front into
County Warning Area later this evening. Combination of front/shortwave should
produce a few -tsra across the northwest 2/5ths of the County Warning Area
overnight. Low level jet will crank ahead of frontal boundary...but
best Theta-E advection will be northeast of County Warning Area. Main effect will
likely be warmer temperatures over south central South Dakota for tonight and
possible St intrusion over the far east late.

Friday...cold front exits County Warning Area with a few breezy spots as boundary
layer mixes and weak cool advection continues. -Tsra possible near
cold front given weak shortwave moving through County Warning Area late morning
through mid-afternoon...but chances will be low. Temperatures Friday
tricky with mixing battling weak cool air advection. Have shot
down the middle with forecast.

Friday night...clearing skies expected as -tsra chances quickly push
south of County Warning Area. Temperatures near guidance.


Long term...Saturday through Thursday
issued at 222 PM MDT Thursday Sep 18 2014

Upper level trough quickly shifts east as another upper ridge over the
western Continental U.S. Rebuilds. Northwest flow over the forecast area will
keep conditions dry for the weekend with seasonal temperatures.
Models show agreement with a weak cut-off low crossing the northern
plains Monday into Wednesday. With return flow setting up bringing
moisture back into the area...storms are expected to develop as the
low pushes through. Drier air is expected to return by Wednesday.
Temperatures should remain near to just above seasonal averages
through much of next week.


Aviation...(for the 00z tafs through 00z Friday evening)
issued at 428 PM MDT Thursday Sep 18 2014

Low level jet will develop across the western South Dakota plains this evening
and continue overnight...and will provide a brief period of low
level wind shear during the late evening and early morning time
period. A cold front will then cross the area late tonight/early
Friday morning...bringing an end to the low level wind shear...with
gusty northwest winds behind the front. Some isolated -shra/-tsra are
possible with the frontal passage with MVFR conditions in any
heavy showers. Some IFR stratus is expected to creep northward into
scntrl South Dakota after midnight.


Unr watches/warnings/advisories...
South Dakota...none.


Short term...helgeson
long term...13

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