Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 210913

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
313 AM MDT Wed Mar 21 2018

.DISCUSSION...(Today Through Tuesday)
Issued at 238 AM MDT Wed Mar 21 2018

Latest upper analysis depicts an upper ridge building over the
western CONUS. At the surface, light southwesterly winds will
become southeasterly this afternoon as a high pressure center
strengthens over the central plains. With the ridge building to
the west, dry and warmer weather is expected today with highs
mainly in the mid 40s to mid 50s. Cooler temperatures will occur
over northwestern South Dakota where the coverage of the snow
pack is most extensive.

Due to relatively moist southeasterly flow have added a mention
of fog for tonight into Thursday morning. On Thursday synoptic
scale subsidence associated with the upper ridge building over the
forecast area will lead to dry weather and warmer temperatures.
As the upper ridge shifts eastward on Thursday night as series of
disturbances in the southwesterly flow aloft will bring a good
chance of precipitation to much of the area. Due to strong low and
mid level warm advection, is appears that the precipitation will
be all in the form of rain from Thursday night into Friday.
Saturday appears to be dry again with warmer than average
temperatures as weak upper ridging develops over the area. After
that ridge shifts off to the east, another series of weak
disturbances will cross the forecast area in southwesterly flow
aloft, bringing chances of rain or snow into early next week.


.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 238 AM MDT Wed Mar 21 2018

VFR conditions are expected at KGCC/KRAP through the TAF period.
Light southerly winds tonight into Wednesday.

Tonight, patchy BR/FG may again develop, particularly in low-lying
areas of the SD plains with relatively fresh snowpack. Should fog
develop, MVFR/IFR and localized LIFR conditions will be possible.
Have kept mention of fog out of KRAP TAF as confidence that fog
will set in at the terminal is low.




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