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

Short term...today through Friday night
issued at 231 am MDT Thursday Sep 18 2014

Ridge flattening disturbance will push through the
region in the period...supporting warm conditions with a slight
chance for a shra/ts. Massive western Continental U.S. Ridge will shift east
today...with the associated thermal ridge advecting over the forecast area
today. Weak positive Theta-E advection combined with steep middle level lapse
rates and ample middle level moisture has supported a few rain showers/ts
earlier over the eastern forecast area. Associated forcing will trend east of
the forecast area as the ridge builds east...ending any precipitation chances before
dawn most places. Otherwise...upper level ridging will be ongoing
into this afternoon ahead of the Pacific northwest shortwave trough. This
trough will push into the region this evening and support ejection
of the Lee side trough in place...with slight chances for showers
and ts spreading northwest to southeast across the forecast area through Friday.

Today/tonight...dry weather expected today with weak shortwave
ridging through this afternoon. Thermal ridge will time over the
region at peak heating...supporting warm temperatures most places...with
80s and 90s expected. Breezy southerly winds expected given ongoing
surface pressure falls and associated gradient flow...breeziest over
scentral South Dakota. Upper level trough and associated jet streak will
approach the region this evening...with a ll Theta-E ridge
present....mainly across the northern zones. Isolated to scattered convection
will push into the northwest zones this evening...with the best chance for
any activity over the far northwest South Dakota zones through tonight. Given ml
convective available potential energy at or above 1000 j/kg with bulk 0-6km shear in excess of 40 knots...a
few stronger cells are very well possible over northwest South Dakota. Warm overnight
lows expected most places given partially mixed bl with warm thermal
fields...especially in Lee of the Black Hills where terrain induced
downsloping is expected per pressure falls.

Friday...ll Theta-E ridge and associated ll trough will shift southeast
across the forecast area with slight chances for rain showers/ts at or above this feature given
synoptic forcing and instability. Not too excited about precipitation
chances given lack of appreciable upper level forcing with the bulk
of lsa passing north of the forecast area. Hence...relegated probability of precipitation to slight
chance outside the Black Hills. Cooler conditions expected western
half with cold air advection ongoing there. Ll Theta-E ridge will slowly shift
south through Friday night with lingering chances for shra/ts...especially
as another jet streak pushes southeast into the northern plains and forces
additional lsa. Retained low probability of precipitation across the far south through much
of Friday night for this. Cooler conditions expected all places with
cold air advection ongoing across the forecast area.

&&

Long term...Saturday through Wednesday
issued at 231 am 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.
Medium range model solutions for next week bring a weak cut-off low
into the Central Plains late Monday into Tuesday. Surface high
shifts east during this time...so southerly return flow should bring
some moisture back into the area. This combination should bring at
least a small chance for some showers and thunderstorms to parts of
the area for Monday afternoon into Tuesday. Temperatures should
remain close to seasonal averages through much of next week.

&&

Aviation...for the 12z tafs through 12z Friday morning
issued at 231 am MDT Thursday Sep 18 2014

VFR conditions are expected through Friday morning. The exception
may be some fog/low stratus from early this morning through 18z
across southern portions of South Dakota...from Pine Ridge through
Winner.

&&

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

$$

Short term...jc
long term...15
aviation...15

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