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
934 PM MDT Thursday Jul 31 2014

Update...
issued at 931 PM MDT Thursday Jul 31 2014

A small cluster of thunderstorms just east of Rapid City continues to push
southeastward...with radar trends suggesting a decrease in this activity.
Only change to forecast was to add small probability of precipitation into parts of southwestern South Dakota to
account for this activity.

&&

Short term...this evening through Friday night
issued at 216 PM MDT Thursday Jul 31 2014

A ridge will move over the western Continental U.S. Through Saturday. Weak
short-wave troughs/subtle disturbances will rotate around this
ridge and move southeast across the forecast area. Forcing for
upward/downward motion will be weak...and moisture and instability
will be marginal. Thicknesses will be steady to slowly rising
through the short term. As a result...only small chances of
thunderstorms are expected...along with temperatures near average.

For this afternoon/evening...MLCAPE of near 500 j/kg and limited
forcing for upward motion will bring a few thunderstorms to the
Black Hills and parts of western South Dakota. Anything that does develop
should diminish early in the evening...and weak cape/shear
indicates severe weather will not occur.

Later tonight..a subtle short-wave trough moves toward the County Warning Area with
weak q-vector convergence by 12z over the western County Warning Area. Low-level warm
advection will be focused over northwestern South Dakota as a surface low moves to
near far northwestern South Dakota. With MUCAPE around 250 j/kg...may see development
of thunderstorms late over the northeastern County Warning Area.

On Friday...weak q-vector convergence is prognosticated as the short-wave
trough progresses across the County Warning Area. Moisture and instability will
increase relative to today...and thus there will be a somewhat
better and more widespread chance of thunderstorms...especially in
the afternoon. However...cape and deep-layer shear will continue to
be relatively weak and thus do not expect organized severe weather.

On Friday night...the short-wave trough will slowly exit the
County Warning Area...but thunderstorms will linger through the evening...especially
in parts of south-central South Dakota where a surface low will be
present. Otherwise...clearing skies will work into northwestern
areas.

&&

Long term...Saturday through Thursday
issued at 216 PM MDT Thursday Jul 31 2014

Upper level ridge remains across the western Continental U.S. Through the
weekend. With lack of forcing...minimal thunderstorm activity
expected Saturday/Sunday. Temperatures will be near average for
the weekend. Models in decent agreement with ridge breaking down
Monday/Tuesday...with middle level moisture plume and embedded
trough/weak closed low lifting northeastward through the Great Basin
into the northern plains. This will bring an increase in
thunderstorm activity and slightly cooler temperatures.

&&

Aviation...(for the 06z tafs through 06z Friday night)
issued at 931 PM MDT Thursday Jul 31 2014

Mainly VFR conditions will prevail through the forecast period.
Isolated -tsra are possible tonight...with local MVFR visibility. A
slightly better chance of -tsra expected Friday afternoon...with local
MVFR visibility.

&&

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

$$

Update...Johnson
short term...bunkers
long term...7
aviation...Johnson

National Weather Service Glossary of Abbreviations