Area Forecast Discussion
Issued by NWS Rapid City, SD
FXUS63 KUNR 271128
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
428 AM MST Sun Nov 27 2016
.SHORT TERM...(Today Through Monday Night)
Issued at 245 AM MST Sun Nov 27 2016
Current surface map places elongated area of low pressure from
southern Montana into eastern Colorado. Upper level trof is moving
into the central Rockies. Models in decent agreement in the short
term. Upper trof moves into the central/northern plains this
afternoon with 700-500mb low closing off over central/eastern South
Dakota this evening. Surface low deepens across Nebraska this
afternoon and tracks into eastern South Dakota this evening. Low
become vertically stacked across northeast South Dakota/southeast
North Dakota Monday/Monday night.
Steep mid level lapse rates and strong forcing will bring showers
to the area this afternoon and evening, mainly across south
central South Dakota. For much of tonight, main area of
precipitation will be east of the forecast area. However, some
rain/snow showers possible across northwest and south central
South Dakota along with snow showers for the Black Hills.
Monday/Monday night Trowal develops on back side of upper low,
with snow wrapping back into northeast Wyoming/western South
Dakota. Far northwest South Dakota may see some light snow
accumulation Monday afternoon. Increasing low level moisture and
steep low level lapse rates Monday night will result in upslope
enhancement across the northern Black Hills.
Tight pressure gradient will result in strong northwest winds
Monday into Monday night. With combination of wind and falling
snow, poor visibility expected across northwest South Dakota.
Will likely need winter weather advisory for northwest South
Dakota with later forecasts.
.LONG TERM...(Tuesday Through Saturday)
Issued at 245 AM MST Sun Nov 27 2016
Stacked low pressure system will likely be positioned
somewhere over far eastern SD or west-central MN Tuesday morning,
very slowly moving east through Tuesday night. Bands of wrap-around
precipitation will slide south across a good portion of the CWA
Tuesday, then gradually diminish Tuesday night. The heaviest
snowfall will be over the northern Black Hills, where upslope
enhanced snowfall can be expected. Gusty winds across the plains
will produce some areas of blowing snow. Snowfall totals of 6 to 12
inches are likely over much of the northern hills by the time the
snow tapers off late Tuesday night, with locally higher amounts
possible. Portions of far northeast WY into northwest SD will see up
to a few inches of accumulation, as well as along the Pine Ridge.
The Rapid City area, the southern Black Hills, and far southwest SD
will likely see little in the way of snowfall with dry downsloping
flow in place.
Conditions will improve in most areas by Wednesday morning, with
lingering areas of light snow or flurries possible in some areas. A
drier, but colder, pattern is then expected through the rest of the
week. The next west coast system is progged by most models to slide
south into the southwest US late in the week, keeping our area in
drier and weaker northern stream flow. Highs will mostly be in the
upper 20s and 30s through the end of the week.
.AVIATION...(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 428 AM MST Sun Nov 27 2016
VFR conditions are generally expected through the afternoon
hours. There will be a chance for rain showers late this afternoon
over southern SD and the Black Hills, becoming a chance for rain
and snow showers over a good portion of western SD tonight. Local
MVFR/IFR conditions are expected tonight. Gusty northwesterly
winds will develop from west to east across the forecast area
late this afternoon and evening behind a passing area of low
SD...Winter Storm Watch from Monday afternoon through late Tuesday
night for SDZ024-025-028.
WY...Winter Storm Watch from Monday afternoon through late Tuesday
night for WYZ057.