Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 161514

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
914 AM MDT Sat Sep 16 2017

Issued at 910 AM MDT Sat Sep 16 2017

The forecast has been updated to lower PoPs substantially through
this morning and early afternoon. The latest radar shows minimal
returns across the area, and satellite images and short-term high-
res models point to mainly dry conditions through the rest of the
morning and the first part of the afternoon. There is a signal of
an area of showers developing over the southwestern CWA by mid-
afternoon as the last short-wave trough rotates around the upper
low. The showers should dissipate by 01z.


.DISCUSSION...(Today Through Friday)
Issued at 243 AM MDT Sat Sep 16 2017

Latest analysis shows an upper trough over western MT/WY producing
moist southwesterly flow aloft over the forecast area. At the
surface, a trough of low pressure extends from MN into sern SD and
then swrn Neb. An area of cool high pressure is moving into the
forecast area from the northwest.

Lift associated with a shortwave rotating around the upper trough
is currently pushing an area of rain northward into parts of
southwestern and south central South Dakota. That precipitation
will continue to move northeastward and out of the forecast area
later this morning, however isolated to scattered showers may
continue over south central SD into the early afternoon. The cool
upper trough will cross the forecast area today and steep lapse
rates will lead to diurnally enhanced isolated to scattered
showers today, although drier air moving into the region may
decrease the chances of showers somewhat later this afternoon.

The cool sfc high will settle across the forecast area tonight
with clearing skies and light winds. Patchy frost may result,
especially in low lying areas on the plains.

The forecast models remain in decent agreement next week with
another deep trof moving into the western CONUS. Shortwave ridging
ahead of the trof will bring warm and dry conditions
Monday/Tuesday with cold front crossing the area Tuesday night.
Temperatures will be cooler for the second half of the week with
increasing chances of precipitation.


.AVIATION...(For the 12Z TAFS Through 12Z Sunday Morning)
Issued At 446 AM MDT Sat Sep 16 2017

Showers and thunderstorms will continue to move across south
central SD this morning, with some additional showers developing
this afternoon. MVFR/IFR conditions in low clouds and
showers/storms will gradually improve to VFR late this afternoon
and this evening as skies clear.




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