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
220 am MDT Thursday Jul 10 2014

Short term...today through Friday night
issued at 220 am MDT Thursday Jul 10 2014

Active westerly flow will continue in the period as
several impulses advance around the periphery of the western Continental U.S.
Ridge. Ll frontal zone will waver across the area...providing the
focus for shra/ts...with some storms possibly becoming severe. One
such impulse is in the process of advecting through the western
forecast area...supporting elevated positive Theta-E advection...evidence well at 700 mb. This
impulse will help lift the nearly stalled frontal boundary back
north as a warm front...with another impulse later this afternoon
ejecting into the area and supporting a surface trough through the
area...and providing the focus for renewed ts development this
afternoon. Stalled upper trough over the eastern Pacific will continue
to support SW flow impulses into the region through Friday.

Today...shra/ts cluster will continue to shift east across the
western half of the forecast area...being aided by vigorous positive Theta-E advection at
the base of a staunch eml. Convection is expected to spread into
western South Dakota...possibly lingering into late morning. Ample deep layer
moisture will build into the region...with ll Gomex moisture
coupling with upper level monsoon moisture from the SW Continental U.S.. this
will support precipitable water values well over one inch across much of the
forecast area...approaching 2 inches over scentral South Dakota. Some threat for
localized heavy rain...and potential flash flooding if back build
cells develop. However...certainly not high enough for issuance of a
Flash Flood Watch...given storm motion vectors. The main concern
today will be the threat for severe storms. Morning convention may
support a hail threat with stronger cores given deep layer bulk
shear values in excess of 40 knots. However...the main concern for
severe weather will be with afternoon and evening ts/S as the next
impulse advects into the region. Ample ll moisture under steep middle
level lapse rates will support ml cape in excess of 2000 j/kg over
much of the area...especially if sufficient insolation is reached...which
may be an issue early in the afternoon given elevated convection and
clouds. Surface trough will be in place across the region this afternoon
per this morning/S impulse. This feature will provide the focus for
new convection this afternoon...with the next approaching impulse.
Storms will also likely fire over the northern/central Black Hills
where capping will be weak and ll convergence strong. Passing upper
jet streak will support deep layer shear in excess of 35 knots
across most of the region and when coupled with ml cape expected in
excess of 2000 j/kg...storms will have a good chance to grow upscale
and become severe...especially across the Black Hills and southeast into scentral
South Dakota. Have adjusted probability of precipitation for this. Convection will trend east through
evening...with the lingering ll frontal zone providing focus for
possible elevated storms overnight across southern areas.

Friday...another impulse will support an undulation of the ll
frontal zone in place...supporting chances for shra/ts...especially in the
late afternoon and overnight. Storms will likely fire over Wyoming and
shift east across the forecast area through through Friday night. Increasing
fast flow aloft per the settling middle level jet will support a severe
threat across the area...especially when coupled with ample ll moisture and
resulting cape along and near the stalled frontal zone across the
region. Adjusted probability of precipitation accordingly. Also adjusted high temperatures down Friday
given concerns on cloud cover/precip/and ll easterly moist upslope
flow.

&&

Long term...Saturday through Wednesday
issued at 220 am MDT Thursday Jul 10 2014

Upper level ridging will be in place across much of the western
Continental U.S. During the extended period. Northwesterly flow aloft will also
persist over the northern plains as an upper low drifts across south
central Canada into the Great Lakes. A series of shortwaves will
move southeastward across the area Saturday into Sunday...bringing a
chance of showers and thunderstorms. Temperatures will be near to
slightly above average this weekend. Cooler and drier weather is
expected for the first half of next week as cold front pushes into
the region.

&&

Aviation...for the 12z tafs through 12z Friday morning
issued at 220 am MDT Thursday Jul 10 2014

Scattered showers and thunderstorms are expected today through this
evening across much of the area. These storms could produce brief
MVFR conditions. 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