Area Forecast Discussion
Issued by NWS Rapid City, SD

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240
FXUS63 KUNR 232017
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
217 PM MDT Fri Sep 23 2016

.SHORT TERM...(This Evening Through Saturday Night)
Issued at 200 PM MDT Fri Sep 23 2016

20z surface analysis shows low pressure centered over eastern
colorado with a warm front arcing northward from southwestern into
central and eastern South Dakota. A surface trough extends
northward from the low into northeastern Wyoming. The surface low
is expected to track quickly northward across western South Dakota
tonight and into eastern Montana/western North Dakota on Saturday
morning. The upper low is located over far southwestern Wyoming
this afternoon and will track eastward tonight...reaching the
Black Hills area on Saturday morning. Temperatures have risen into
the mid 90s in the area of sunshine south of the warm front over
south central South Dakota, with lower 60s in the region of
stratus over far northwestern South Dakota. A band of showers and
thunderstorms has already developed in the area of strongest lift
to the west of the sfc trough in central Wyoming. That region will
shift northeastward during the rest of this afternoon and
evening. While instability isn`t all that strong over northeastern
Wyoming and western South Dakota, 0-6km Bulk Shear is around 50kts
already over northeastern Wyoming. The shear is expected to
increase over western SD this afternoon and evening as the sfc low
moves northward and the upper low approaches from the east. Severe
thunderstorms are possible.

A fast moving cold front will push into northwestern CWA Saturday
afternoon with gusty west to northwest winds. NAM weakest with GFS
showing 45-55kt 850mb wind and well-defined cold air advection.
Have issued wind headlines for parts of nwrn SD from late Saturday
afternoon through Saturday night.

.LONG TERM...(Sunday Through Friday)
Issued at 200 PM MDT Fri Sep 23 2016

Upper trof associated with storm system will cross the
western Dakotas Sunday with northwest flow over the forecast area.
Some showers still possible early on Sunday over far northwestern
SD, with clearing skies through the day. Tight pressure gradient
will continue over SD, although NW winds will decrease slightly over
northwestern SD, winds will increase over the rest of the SD
plains. Temperatures will start warming over northwestern WY and
far western SD Sunday, but cool air advection persists over
central SD. An upper ridge will build over the Rockies for warmer
and drier weather through midweek.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Saturday)
Issued At 200 PM MDT Fri Sep 23 2016

Skies are starting to clear acrs the srn half of
the forecast area with IFR cigs/fog contg acrs nwrn SD. Shwrs and
strg tstms wl dvlp ovr nern WY in the aftn, then move into wrn SD by
early even. MVFR/IFR cigs wl form behind the low and cont thru much
of the night alg with shwrs. Gusty NW winds wl incrs behind the low,
then bcm westerly Sat mrng.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory from 5 PM Saturday to 6 AM MDT Sunday for SDZ014-
     025-026-031-032-072-073.

     High Wind Watch from Saturday afternoon through late Saturday
     night for SDZ001-002-012-013.

WY...None.
&&

$$

SHORT TERM...10
LONG TERM...55
AVIATION...55



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