Scientific Forecaster Discussion
fxus63 kunr 192343
Area forecast discussion for western South Dakota and northeastern Wyoming
National Weather Service Rapid City South Dakota
443 PM MST Tue Nov 19 2019
Discussion...(this evening through tuesday)
issued at 201 PM MST Tue Nov 19 2019
Water vapor shows dirty ridge extending through the northern
rockies into the northern plains, with splitting trof along the
West Coast. East-southeast surface winds are in place in between
ridge over the far eastern Dakotas and Lee trof along the Rocky
Mountain front. Mild temps once again this afternoon with readings
in the upper 40s and 50s.
Northern stream trof quickly advances into the northern rockies
by late tonight with surface front pushing into our western zones.
Could be a bit of fog ahead of the front but majority of models
keep the boundary layer relatively dry, so have cut back on fog
mention from previous forecast.
Low stratus will spread south across the area behind the front on
Wednesday with relatively dry air above. There will likely be
some light precip developing behind the front, and without much if
any ice in the cloud layer precip type may be more drizzly. Temps
behind the front should remain fairly steady or slowly fall. Best
chance for freezing drizzle will be across northeast Wyoming and
northwest SD, but there is some chance that temps could fall near
or below freezing further south on the South Dakota plains during the day,
and subsequently result in freezing drizzle. Deeper moisture
should arrive later in the day and evening to switch any freezing
precip over to snow. Snow should then end from north to south by
Thursday morning. Best chance to see a couple inches of
accumulating snow will be across northeast Wyoming and the northern
Black Hills. Aside from the precip, expect gusty northwest winds
especially on the South Dakota plains. Strongest winds should be just east
of the Black Hills and could be near advisory criteria.
A stretch of dry weather is then expected through the weekend.
Chilly highs on Thursday will transition to temps into the 50s
over the weekend. Next trof moves in early next week for next
chance of precip and cooler weather.
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 443 PM MST Tue Nov 19 2019
VFR conditions will continue this evening. Late tonight, winds
will become northwesterly and breezy behind a cold front. Fog,
drizzle, and freezing drizzle is expected to develop ahead of
this system. Snow will then begin moving into the area on
Wednesday from the west. Northwesterly winds will increase to 20
to 30 kts, with gusts of 30 to 40 kts, particularly across the
western South Dakota plains.