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Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota
545 PM MDT Thursday Jul 30 2015

Short term...this evening through Friday night
issued at 229 PM MDT Thursday Jul 30 2015

20z surface analysis shows weak high pressure over the forecast area
producing mostly sunny skies. A weak trough over the eastern
Dakotas has tightened the surface pressure gradient and is helping to
produce breezy conditions over parts of northwestern and central
South Dakota.

Tonight/Friday...the upper ridge will continue to build over the
western Continental U.S. With a thermal ridge expanding eastward over the
forecast area. On Friday southerly return flow will develop as
the surface high shifts east. MLCAPE will increase to 250-750j/kg by
late Friday afternoon over parts of northestern Wyoming...the Black Hills and southwestern South Dakota.
Models indicate that a weak shortwave may provide enough forcing
to overcome the cin by late afternoon so have included a slight chance
of thunderstorms over those areas from late afternoon into early
evening. Highs on the plains on Friday are expected to range from
the upper 80s to lower 90s with middle 70s to middle 80s in the Black Hills.

Long term...Saturday through Thursday
issued at 229 PM MDT Thursday Jul 30 2015

Medium range models are in good agreement through the
first part of the extended period and then differ some toward the
middle of next week...when conditions are expected to become at
least a bit more unsettled. Drier northwest flow aloft will remain
across the region through the weekend and into Monday morning. Other
than the possibility for a few showers and thunderstorms from far
southwest into south central South Dakota on Saturday...mainly dry conditions
should persist through at least early Monday. Temperatures will be above
average through the weekend...with highs in the 90s across much of
the plains...80s in the Black Hills.

As mentioned...the weather pattern will likely become more unsettled
for the middle part of the week...especially Tuesday... as east to
southeast winds bring increasing moisture and flow aloft become more
zonal. Models are still in some disagreement on the timing of
disturbances passing across...with the European model (ecmwf) still showing more
potential for storms then the GFS. Although there is plenty of
uncertainty...Tuesday and Tuesday night still look like the best
periods for precipitation potential at this time. Temperatures will be slightly
cooler next week...but still around average.

&&

Aviation...for the 00z tafs through 00z Friday evening
issued at 542 PM MDT Thursday Jul 30 2015

Clear to scattered clouds through Friday morning. As surface hi pressure builds over forecast
area...north winds will diminish and become lgt/vrbl.

&&

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

$$

Short term...10
long term...26
aviation...55

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