Scientific Forecaster Discussion
Area forecast discussion for western South Dakota and northeastern Wyoming
National Weather Service Rapid City South Dakota
1029 PM MST Monday Mar 2 2015
Short term...this evening through Tuesday night
issued at 223 PM MST Monday Mar 2 2015
21z surface analysis had low pressure over central Colorado with trough
into eastern ND. Arctic boundary nosing into central Montana. Water
vapour had two shortwaves of interest...one over southern ab and
another over southwest Utah. Models are in decent agreement with
evolution of these features.
Tonight/Tuesday...Utah shortwave ejects into central NE by 12z Tuesday
and then scoots east. Ab shortwave will drop into Montana. Previous
guidance suggested these waves might merge...but latest guidance and
satellite loops indicate this won't happen. As a result...Utah
shortwave will rocket to the northeast on 150kt jet streak. Lift in
left exit region of jet will be quite vigorous causing
cyclogenesis over Colorado as surface low moves into eastern NE 12z
Tuesday and then into the Great Lakes by 00z Wednesday. Low will
grab Arctic air. Narrow band of well-defined frontogenesis
develops at leading edge of Arctic air...linking up with synoptic
lift. Band of light-moderate snow will occur from southwest into
central South Dakota with 3-5 inches likely by midday Tuesday. Additional
lift from secondary shortwave will keep -sn going over northeast
Wyoming/Black Hills through Tuesday afternoon where slightly higher
amounts expected. Some upslope enhancement over the northern Black
Hills per Froude numbers/boundary layer moisture profile.
Main issue will be gradient between 1035mb Arctic high and 1002mb
surface low resulting in gusty northerly winds. Blsn will become a
problem over much of the plains with worst winds/snow from kien to
kphp to kicr...and thus have upgraded to Winter Storm Warning for
those areas. Rest of County Warning Area looks OK with advisory for now...but later
shifts will need to monitor final position of snow band.
Tuesday night...bitterly cold wind chills expected with wind chill
advisories likely over parts of the area.
Long term...Wednesday through Monday
issued at 223 PM MST Monday Mar 2 2015
Arctic high slides southeast across the Dakotas on
Wednesday...with bitter cold air remaining across the area. Warmer
air will begin to build into the region later Wednesday night and
especially on Thursday. Medium range models generally in good
agreement for the rest of the week and the weekend as mainly dry
northwest flow aloft remains through the period. A ridge over the
western Continental U.S. Will slowly move east into The Rockies over the
weekend. Temperatures will be above average Friday through
Monday...with highs in the 40s and 50s.
Aviation...for the 06z tafs through 06z Tuesday night
issued at 1027 PM MST Monday Mar 2 2015
A strong weather disturbance will move into northeastern Wyoming
and southwestern South Dakota tonight...with flight conditions
deteriorating quickly to IFR/LIFR in snow. Snow and IFR/LIFR
conditions will spread quickly north and east across most of the
County Warning Area overnight...with the heaviest snowfall generally expected
across portions of the Black Hills and far southwest South Dakota...eastward
into south central South Dakota. Snow should taper off quickly in most areas
A strong Arctic front will also drop south through the forecast area
tonight...increasing north winds to 20 to 35 miles per hour with higher gusts
through Tuesday afternoon. This will produce blowing snow and
greatly reduced visibilities at times.
South Dakota...Winter Weather Advisory until 5 PM MST Tuesday for sdz024-025-
Winter Storm Warning until noon MST /1 PM CST/ Tuesday for
Winter Storm Warning until 5 PM MST Tuesday for sdz027-029-041-
Winter Storm Warning until noon MST Tuesday for sdz030-031-042.
Winter Weather Advisory until noon MST Tuesday for sdz001-002-
Winter Weather Advisory until noon MST Tuesday for sdz026-073.
Wyoming...Winter Weather Advisory until 5 PM MST Tuesday for wyz054>058-