Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 261711

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1111 AM MDT Sun Mar 26 2017

.SHORT TERM...(Today Through Monday Night)
Issued at 216 AM MDT Sun Mar 26 2017

08z surface analysis had low over central CO with cold front into
western SD. Water vapour had upper trough from MT into CO, moving
east. Main energy south of the CWA, but lift under right entrance
region of 90kt jet streak producing light precipitation in the
west. Evolution of system continues to be slower with lift being
wasted on saturation and thus, lots of virga.

Today, aforementioned system moves east and weakens. Still looks
like western portions of the CWA will see precipitation, but
amounts will be light. An area of stratus and fog east of the CWA
will push west early this morning into far eastern portions of the
CWA, but then mix out by midday. Temperatures will be seasonal.

Tonight through Monday afternoon, upper ridge builds into the
northern plains ahead of another upper trough moving from the west
coast into the Rockies. Mainly dry weather expected.

Monday night, upper trough splits with several pieces of energy
moving into the plains states. Main piece should stay well south of
the CWA with another piece along the US/Canadian borders. Middle
piece of energy main concern with 00z guidance is good agreement
bringing precipitation to the CWA, especially over southwest SD.
Temperatures will be marginal for snow.

.LONG TERM...(Tuesday Through Saturday)
Issued at 216 AM MDT Sun Mar 26 2017

Upper trough continues to affect CWA Tuesday. Inverted surface
trough pokes into the Black Hills with increasing low level
upslope flow in response to weak mid-level circulation over
eastern WY. Models in good agreement with blob of precipitation
over the CWA, especially over the Black Hills and southwest SD.
1-2" liquid forecast by some guidance with some guidance showing
significant snow over the higher terrain. Not convinced given
splitting upper trough scenario and marginal low level
temperatures. Snowfall would have to develop mainly due to
dynamic cooling, which the models do show, but may be overdone.
Bottom line, high PoPs warranted along with accumulating snow over
the higher Black Hills. Accumulations on the plains looks minimal
right now.

Wednesday and Thursday, weak upper ridge brings drier weather. Next
system drops by as another splitting trough for Friday and Saturday
with chances for precipitation.


.AVIATION...(For the 18Z TAFS Through 18Z Monday)
Issued At 1107 AM MDT Sun Mar 26 2017

Widespread MVFR and areas of IFR conditions in rain and higher
elevation snow will continue for much of the aftn hours across
the Blkhls and wrn SD. MVFR conditions across nern WY will become
VFR this aftn. VFR conditions will then spread into the Blkhls and
far wrn SD this evening, but MVFR cigs may remain on parts of the
SD plains through the night.




SHORT TERM...Helgeson
LONG TERM...Helgeson
AVIATION...Johnson is the U.S. government's official web portal to all federal, state and local government web resources and services.