Area forecast discussion for western South Dakota and northeastern Wyoming
National Weather Service Rapid City South Dakota
318 am MDT Wednesday Jun 19 2013
Short term...today through Thursday night
issued at 317 am MDT Wednesday Jun 19 2013
Current surface analysis shows low pressure over western Montana into
eastern Idaho...with warm front extending east-southeast across
southern Montana into the Black Hills area. High pressure is to the
east of the region. Pressure gradient is tightening over the
northern High Plains. Upper level analysis has low pressure along
the Pacific northwest coast...finally beginning to move slowly eastward.
Ridge is in place over the northern High Plains. Weak disturbance
passing through the ridge is bringing showers and storms to much
of central Nebraska...with the northern edge of precipitation clipping parts of
southwestern into south central South Dakota. Strong low level jet is also
in place across these areas. Showers and storms could begin to
develop a bit further north across southwestern into south central
South Dakota early this morning with fairly strong Theta-E advection also
occurring. Skies are partly to mostly cloudy across much of the
area with temperatures in the middle 50s to middle 60s at most locations. Winds
are southeasterly...breezy at times across portions of far
southern South Dakota.
Very warm conditions can be expected across the area today as
thermal ridge passes over the area. High temperatures will be in the
80s for most areas...with some lower 90s likely over portions of
northeastern Wyoming. Southeasterly winds will increase later this
morning as temperatures rise and boundary layer mixes out. The strongest
winds look to be across far northwestern South Dakota...where gusts to around
45 miles per hour are expected in the afternoon. Will issue a Wind Advisory for
Harding and Perkins counties. These winds will conitnue to bring low
level moisture into most of the area...especially east of the Black
Hills...with dewpoints rising to the low 60s and possibly middle 60s in
the afternoon across eastern portions of the County Warning Area. A dry line will
develop across central Wyoming by the afternoon and likely make its way
into at least Campbell Colorado Wyoming during the afternoon...bringing
southwesterly winds and low humidities to western portions of
northeastern Wyoming.
The threat for isolated thunderstorms can be expected throughout the
day acorss far eastern portions of the County Warning Area...but mainly this
morning...as low level jet and strong Theta-E advection remain over
this area. Increasing moisture will produce a very unstable air mass
over western South Dakota by the afternoon...but strong capping inversion and
lack of upper level forcing will make it very difficult for any
storms to develop beyond this morning. However...if a storm were to
get going...it would be in a very favorable environment to become
severe. Will keep a slight chance for storms late this afternoon
over the Black Hills as cap is prognosticated to weaken enough that a storm
would be possible. The better chances for precipitation will generally be
tonight...though any activity should be fairly isolated...as low
level jet strengthens again in the evening and a weak cold front
approaches from the west. The environment would still be favorable
for a strong to severe storm...especially in the evening.
Cold front will move across western areas Thursday morning...slowing
down as it moves further east in the afternoon. Chances for storms
look to be mainly across eastern portions of the County Warning Area in vicinity of
the front...especially in the afternoon. A severe storm or two
looks possible toward central South Dakota. Drier and much more stable air
mass will move into western areas. Highs will be in the middle 70s to
middle 80s...warmest toward central South Dakota. Gusty northwesterly winds are
likely behind the front across western areas in the morning and
midday hours...at least for a brief time. As the upper low moves
into the northern rockies by Thursday night...a shortwave is
prognosticated to move northeastward around the low and across the
northern high plaisn. This could bring a few showers and storms
Thursday night...especially to northern and western portions of
the County Warning Area.
&&
Long term...Friday through Tuesday
issued at 317 am MDT Wednesday Jun 19 2013
Southwest flow aloft is expected over the County Warning Area Friday/Saturday as
an upper low spins over the northern rockies and upper level ridge
is anchored over the Midwest. Several surface boundaries will
meander through the County Warning Area with a series of shortwaves ahead of upper
low. Moderate/strong instability will develop with easterly
component to boundary layer wind supporting increasing low level
moisture. Could be an active period for thunderstorms and rain. Temperatures will be
near guidance.
Sunday...upper low ejects into south central Canada bringing last
round of thunderstorms and rain to the area. Much drier air will filter in behind
system. Monday/Tuesday/Wednesday...large scale upper level ridge
slowly develops over The Rockies and moves into the plains states. A
couple of ridge riders might bring isolated thunderstorms and rain to parts of the
County Warning Area...but it should largely remain dry with temperatures above 90f
over parts of the area.
&&
Aviation...for the 12z tafs through 12z Thursday morning
issued at 317 am MDT Wednesday Jun 19 2013
Low level jet will bring low level wind shear to central
South Dakota early this morning. Gusty southeast winds will then develop on
the South Dakota plains today. Chances for thunderstorms and rain will be small this
afternoon/evening ahead of a cool front...but if any storms develop
they will create local LIFR conditions. The cool front will slowly
move into the County Warning Area overnight.
&&
Unr watches/warnings/advisories...
South Dakota...Wind Advisory from 9 am this morning to 9 PM MDT this evening
for sdz001-002.
Wyoming...none.
&&
$$
Short term...26
long term...helgeson
aviation...helgeson
