Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 110417
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1017 PM MDT Thu Aug 10 2017

.DISCUSSION...(This Evening Through Thursday)
Issued at 250 PM MDT Thu Aug 10 2017

Broad upper trough continues across the eastern half of the CWA with
upper ridging/rex block centered across the Pac NW. Quiet weather is
across the area today as surface high sits across the northern High
Plains. Quiet weather will continue tonight with lows in the mid 40s
to mid 50s. Light winds today will become southeasterly overnight as
the surface high pushes into the eastern Dakotas. A shortwave across
Alberta will swing down into central/eastern Montana tonight into
Friday morning. Surface low developing over eastern MT Fri morning
will reinforce S/SE low level flow across the CWA bringing some
warmer/more moist air in. Highs will reach the mid 70s to mid 80s.
Storms are progged to develop in the early afternoon across the
Black Hills area...the across the plains during the late
afternoon/evening. MLCAPE looks weaker for Friday than it did
yesterday...at 700-1500 J/KG. Still decent shear...so while overall
severe threat appears to be marginal, think isolated severe storms
will still be possible especially with damaging wind potential as
boundary layer mixes out to inverted V profile.

Storms will redevelop Saturday as the strong upper wave slowly
crosses the Dakotas. The storm potential will largely depend on
the path of the surface low which latest models seem to be
favoring a more southerly track. The best Theta E will be south of
the CWA...and perhaps into edging into the Black Hills area
through south central SD where MLCAPE values will be more
appreciable. Models also showing PWATs increasing to 125-150% of
normal...so there could be good amounts of rainfall in the
stronger storms despite storm motions of 20-30 kt. Upper wave will
leave the area Sat night with quieter weather Sunday. Upper ridge
axis will cross the central plains Monday with deep southwesterly
flow aloft develop heading into the middle of the week. Could see
another round of storms during the time range before cooler and
drier weather return.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 1014 PM MDT Thu Aug 10 2017

VFR conditions are expected through the period. Thunderstorms will
develop across portions of the region Friday. Local MVFR-IFR conds
possible in/near thunderstorms.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION...13
AVIATION...JC



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