Scientific Forecaster Discussion
Area forecast discussion for western South Dakota and northeastern Wyoming
National Weather Service Rapid City South Dakota
1120 am MDT sun Apr 19 2015
issued at 1011 am MDT sun Apr 19 2015
Strong upper trough is sliding southeastward through the northern
plains. Strong mixing combined with a tight pressure gradient has
led to gusty northwest winds across the South Dakota plains. Have
extended the Wind Advisory into south central South Dakota as
Winner is already knocking on the door of advisory criteria. Winds
should persist through the afternoon hours and quickly diminish
early this evening.
Short term...today through Monday night
issued at 313 am MDT sun Apr 19 2015
Current surface analysis shows cold front stretching from eastern
ND to south central South Dakota and the Nebraska Panhandle. Upper level analysis
has low centered over western Kansas...starting to move more quickly
eastward. Northern stream shortwave is located over the western
Dakotas...moving east-southeast rather quickly. Kudx radar shows
lingering light showers over far eastern and southern portions of
the County Warning Area...dissipating as drier air in low levels rushes in behind
the front. Skies have cleared across much of northeast Wyoming and far
western South Dakota. Temperatures are mostly in the 30s across western areas...40s
over most of the western South Dakota plains.
A mainly dry and cool pattern can be expected through early this
week as dry northwest flow from Canada takes over. Gusty northwest
winds can be expected over the next couple of days...especially
during the late morning and afternoon hours...as fairly tight
pressure gradient and deep bl mixing develop.
For today...skies will be variably cloudy in general...some clearing
in the morning...with a good amount of cumulus developing through
the late morning and afternoon as moisture wraps back around the
system from the north. A few light showers or sprinkles are possible
across far northwest South Dakota in the afternoon. Highs will only be in the
upper 40s to middle 50s across the plains...with 40s over the Black
Hills. Northwest winds will increase this morning...with the
strongest winds across the northwest and west central South Dakota plains
during the late morning and afternoon hours. Will issue a Wind
Advisory for these areas...with some gusts to near 50 miles per hour expected.
Winds will decrease toward sunset and clouds will also dissipate.
Lows will be in the 20s and lower 30s with relatively light west to
northwest winds toward morning.
Temperatures will be similar on Monday...though a bit milder over western
areas. Breezy northwest winds will develop across the South Dakota plains
during the late morning and afternoon hours...strongest toward
central South Dakota. Skies will be partly cloudy in general Monday and Monday
Long term...Tuesday through Saturday
issued at 313 am MDT sun Apr 19 2015
Deep eastern noam upper trough will support blocked downstream
flow...as complicated fast flow over the Pacific supports split flow
locally. Large scale upper low over the eastern Pacific will allow a
southern periphery vortex into the SW Continental U.S. By middle next week with
antecedent downstream ridging. This will create a psuedo
baroclinic zone over the region with the warmest conds expected
over the western third of the forecast area. Meanwhile...the eastern Continental U.S.
Upper low will support potential back door cold fronts into the
region...keeping temperatures at Bay. Dry conds will prevail until toward
the end of the week...at which time western Atlantic blocking
looks to diminish...supporting an eastward shift and breakdown of
the western noam ridge and the eventual ejection of the SW Continental U.S.
Upper low. Current deterministic and mean ensemble solutions
continue to track this system through the central/Southern
Plains...with most lsa passing south of the forecast area. Hence...limited
probability of precipitation to low chance and slight chance Thu-Sat.
As alluded to above...given dominant easterly flow...temperatures are
expected to be near or slightly below seasonal norms in the majority
of the period...with a strong influence from the eastern upper low.
Highs will generally be in the 50s and 60s with lows in the 30s.
Aviation...(for the 18z tafs through 18z monday)
issued at 1119 am MDT sun Apr 19 2015
VFR conditions expected through the period. Gusty northwest winds
expected through this evening. Gusty northwest winds will
redevelop on the South Dakota plains Monday.
South Dakota...Wind Advisory until 7 PM MDT /8 PM CDT/ this evening for sdz001-