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Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota
1059 am MDT Wednesday may 27 2015

Short term...today through Thursday night
issued at 308 am MDT Wednesday may 27 2015

Water vapor shows upper low over Washington with negatively tilted wave
rotating rotating through Mt/WY. At the surface...high is centered
over the Central Plains with trough taking shape over eastern Montana/eastern Wyoming.
Scattered rain showers/thunderstorms extend from the Nebraska Panhandle into far southwestern South Dakota in
region of low/middle level Theta-E advection ahead of upper wave.

Today...upper wave will continue its northeastward progression with surface low
developing over the Black Hills by midday. MLCAPE expected to increase
to near 1000j/kg over much of the County warning forecast area with cin eroding quickly by
late morning over northestern Wyoming and far western South Dakota. Convection will intiate
early in the higher terrain of the Black Hills as well as northestern
Wyoming...then intensify as it shifts eastward across the western South Dakota plains. An
area of enhanced MLCAPE of near 1500j/kg along with better shear
will develop along a developing warm front extending from the Black Hills
low into central South Dakota and may result in a few severe storms...and cant
rule out an isolated tornado given intensifying frontal boundary east
of the Black Hills. Heavy rain also a threat...especially across northwestern
South Dakota north of the warm front. Activity will quickly shift North/East of
the County warning forecast area this evening.

Thursday...upper low shifts into the northern rockies with surface front
pushing through our eastern zones. Fairly widespread diurnal convection
expected...with a few severe storms possible along the surface front over
scntrl South Dakota.

Long term...Friday through Tuesday
issued at 308 am MDT Wednesday may 27 2015

Upper level trough shifts east of the northern plains on
Friday as surface high pressure drops south out of Canada. Lingering
showers are expected early on Friday...shifting south and east early
as drier air moves in. By the weekend...cool high pressure resides
across the northern plains with broad upper level ridging developing
late in the weekend. A warm up is expected the following week along
with a return of showers and thunderstorms.

&&

Aviation...for the 18z tafs through 18z Thursday
issued at 1059 am MDT Wednesday may 27 2015

Isolated/scattered -shra/-tsra over south central South Dakota
will continue to shift east. More widespread showers and
thunderstorms are expected this afternoon. VFR conditions expected
outside of precipitation...with MVFR ceilings/visibilities near any storms.

&&

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

$$

Short term...Johnson
long term...15
aviation...pojorlie

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