Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 140921
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
321 AM MDT Thu Sep 14 2017

.DISCUSSION...(Today Through Wednesday)
Issued at 300 AM MDT Thu Sep 14 2017

Latest upper level analysis shows an upper trough swinging across
southwestern Canada and into the northwestern CONUS which is
turning the upper flow over the forecast area from zonal to
southwesterly. At the surface, low pressure is centered over
South Dakota. A disturbance over ND is swinging some weak showers
across central SD.

Beginning today and continuing into the weekend, moist and cooler
air will move into the region as the upper trough approaches and
swings across the northern plains. Chances for precipitation will
increase significantly, especially tonight and on Friday.
Precipitable water values Thursday night and Friday across the
forecast area look to be 1.0 to 1.2" or 175% to 200% of average.
The chance for showers and a few thunderstorms will continue into
next week, but warmer temperatures will return for Monday and
Tuesday.

The system over the next few days is just the start to an overall
weather pattern shift for the area that should last through the end
of the month. It appears as if the typical fall/late September
pattern begins to set up. Zonal to southwesterly flow aloft will
allow moisture and energy to stream into the area from the Pacific
Northwest. This will bring some chances for precipitation, some
windy days, and widely fluctuating day to day temperatures for the
area during the next couple of weeks.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Friday Morning)
Issued At 300 AM MDT Thu Sep 14 2017

Areas MVFR FU will continue through the period.
Isolated/scattered TSRA over northwest SD will end by 12z.
Additional TSRA with local MVFR conditions will develop in the
afternoon over northeast WY and then spread east into western SD
Thursday night. MVFR CIGS will move into northeast WY after 06z
Thursday night.

&&

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

$$

DISCUSSION...10
AVIATION...15



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