Area Forecast Discussion
Issued by NWS Rapid City, SD

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338
FXUS63 KUNR 260818
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
218 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 06Z TAFS Through 06Z Sunday Night)
Issued At 216 AM MDT Sun Mar 26 2017

A cold front will spread MVFR conditions and rain from west to
east through this morning before dissipating this afternoon. Local
IFR conditions expected near the higher terrain as clouds
intersect and some snow mixes in. IFR stratus and fog will affect
far eastern portions of the CWA this morning with some improvement
this afternoon. As storm system weakens and moves east,
improvement expected areawide tonight.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

SHORT TERM...Helgeson
LONG TERM...Helgeson
AVIATION...Helgeson



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