Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 122317

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
517 PM MDT Sun Aug 12 2018

.DISCUSSION...(This Evening Through Sunday)
Issued at 124 PM MDT Sun Aug 12 2018

The upper ridge is starting to break down, as the Pacific NW
trough pushes eastward. Skies across the region are mostly sunny,
with some smoke persisting. Surface low over western ND is
resulting in some breezy southerly winds across the western SD
plains this afternoon. Temperatures are in the 90s.

A cold front will begin moving into the CWA this evening, slowly
crossing the CWA on Monday. Some weak showers/storms will be
possible along the front, mainly across northeastern WY. Skies
tonight will be mostly clear, although some clouds and more smoke
will start to move into the northwestern CWA with the cold front.
Lows tonight will be in the 60s.

Monday will be slightly cooler, with some isolated showers/storms. A
shortwave will bring better chances for precipitation to the area on
Tuesday, along with the coolest temperatures of the week (highs in
the mid 70s to mid 80s). Chances for showers and thunderstorms will
continue into Wednesday. Models are showing another upper ridge
building over the western states for the end of the week, but both
the GFS and ECMWF are in agreement on another shortwave breaking
down this ridge by the weekend. Highs for the latter half of the
week will be in the 80s.


.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 516 PM MDT Sun Aug 12 2018

VFR conditions are expected through the TAF period, although
areas of smoke may lower the VSBY below 10 miles at times.
Southerly winds will diminish this evening. Winds will shift to
the northwest tonight/Monday as a cool front moves over the area.


Issued At 124 PM MDT Sun Aug 12 2018

RH is falling into the teens across much of the CWA, and winds
are gusting to 25 to 35 mph over the western SD plains. Considered
adding northeastern WY to the RFW this afternoon, as obs are
indicating gustier winds than previously forecast. However,
NAM/RAP/HRRR soundings show winds decreasing this afternoon when
RHs fall below 15%. Will keep the RFW as is.


SD...Red Flag Warning until 9 PM MDT this evening for SDZ261>264-266.



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