Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota
226 PM MDT Friday Jul 25 2014

Short term...this evening through Saturday night
issued at 224 PM MDT Friday Jul 25 2014

Weak surface ridge over the region is supporting clear
skies and drier air into the area. Potent northern stream closed
upper low will continue to slowly advect/propagate southeast through the
period...with upper level flow gradually veering northwest. Northern stream
closed upper vortex will slowly shift southeast tonight and partially phase
with a weak impulse rotating around the northern periphery of the SW
Continental U.S. Upper level ridge...supporting chances for rain showers/ts mainly over
scentral South Dakota. Secondary cold front will push southeast across the forecast area Sat
morning as a reflected surface low pushes int the Great Lakes.
Cold air advection/pressure rises/and strong ll flow with deep mixing will support
a breezy day Sat...with cooler conditions expected...especially across the
northwest half as another surface ridge builds into the region.

Tonight...reflected ll positive Theta-E advection per veering ll flow will
support chances for rain showers/ts across much of the southeast half...especially late
tonight. Although lift from passing impulse will be fairly
weak...jet dynamic forcing from a passing jet streak should be
enough to compensate for this...especially in the far southeast. Retained a pop
mention...highest over Tripp County. MUCAPE values at or above 1500 j/kg in
the far southeast coupled with steep middle level lapse rates and ample
effective shear may be enough to support a rotating storm or
two...especially closer to dawn when the best overlap of forcing will be in
place...the timing of which has been pushed back in latest guidance
output. Hence...have trended higher probability of precipitation after 12z in the far
southeast...with a downtrend late morning.

Sat...lingering activity should wane by late morning in the southeast.
However...latest NAM/nmm guidance suggest that a few storms could
linger into early afternoon extreme southeast. For now have left the
afternoon dry there. Secondary cold front will push through the area
with weak cold air advection ensuing...especially the northwest. Deep mixing per clear skies and
decent pgf across the region will support breezy conditions on the
South Dakota plains...especially the northwest portion. A wind advection may be needed there if
current trends continue. Slightly cooler conditions expected
Sat...mainly northwest areas. Cool conditions forecast Sat night with drier
air/clear skies/and slackening winds supporting decent radiational
cooling...especially northwest half. Have lowered mins some.

&&

Long term...Sunday through Friday
issued at 224 PM MDT Friday Jul 25 2014

Upper ridging will dominate across the western Continental U.S. Through the
extended. With the main axis remaining west of the region...overall
northwest flow aloft is expected with a few weak waves crossing through.
This could bring slight chances of storms periodically...but overall
a dry extended period is expected. Temperatures will be near average.

&&

Aviation...for the 00z tafs through 00z Saturday evening
issued at 224 PM MDT Friday Jul 25 2014

Isolated to scattered storms are possible tonight over central South
Dakota. Otherwise VFR conditions are expected through the forecast
period.

&&

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

$$

Short term...jc
long term...13
aviation...13

National Weather Service Glossary of Abbreviations