Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 271042

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
442 AM MDT Thu Jul 27 2017

.DISCUSSION...(Today Through Wednesday)
Issued at 417 AM MDT Thu Jul 27 2017

Upper level analysis shows high pressure beginning to build over
the inter-mountain west with several shortwaves progged to round
the ridge and make their way into the northern plains through the
end of the week. At the surface, high pressure remains across the
area with a weak lee tough/developing stationary front situated
across eastern Wyoming. A few lingering isolated showers continue
to diminish over eastern Wyoming.

For today, moist southerly flow combined with diurnal heating will
provide instability for the development of afternoon storms across
northeastern Wyoming. Scattered convection will develop along the
weak lee trough/developing stationary front. ML CAPE values of 1000
to 1500 J/KG combined with steep low to mid-level lapse rates may
result in a stronger to isolated severe storm or two.

For tonight, shortwave energy currently over Utah should reach the
convection over northeastern Wyoming shortly before sunset. This
energy will allow the convection to drift east and continue across
parts of western South Dakota overnight.

On Friday, deep moisture and ML CAPE of 1000 to 1500 J/KG will be
around and over the Black Hills. Another impulse combined with
diurnal instability will support afternoon thunderstorm development.
Convection will slowly shift east Friday evening. With low-level
southeasterly flow beneath 25 to 35 kt mid-level westerlies, shear
will be sufficient for a few isolated severe storms during the
afternoon and evening.

The upper ridge looks to persist over the western CONUS for the
entire extended period. Several shortwaves will pass through the
flow, supporting near daily chances for convection in portions of
the forecast area. A stronger trough will push through the far
northern plains from a wave passing through southern Canada on
Monday. This may support the best chance for showers and storms.
High temperatures will be in the 80s to 90s with lows in the 60s
through next week.


.AVIATION...(For the 12Z TAFS Through 12Z Friday Morning)
Issued At 438 AM MDT Thu Jul 27 2017

Scattered thunderstorms will develop across northeastern Wyoming
this afternoon, and move into western South Dakota late this
afternoon into this evening. Local MVFR conditions possible with
the thunderstorms, otherwise VFR conditions are expected through
the period.




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