Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 212316

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
516 PM MDT Thu Sep 21 2017

.DISCUSSION...(This Evening Through Thursday)
Issued at 137 PM MDT Thu Sep 21 2017

A large trough across the western CONUS will influence our
weather through the upcoming weekend. At 19z a cold front had
pushed through over 1/2 of the CWA and was from roughly KD07 to
KIEN. This will move rather slowly tonight and Friday, reaching
KICR around 18z Friday, and pushing southeast of the CWA Friday
evening. Aloft, southwest flow will prevail with periodic short-
wave troughs ejecting out of the western CONUS trough about every
24 hours. It looks like one impulse will bring a round of showers
and embedded thunderstorms late Friday and Friday night, with the
best chance of thunderstorms over south-central South Dakota.
Ensemble data then suggest a stronger wave Saturday night into
Sunday with fairly widespread precipitation.

Temperatures will be notably lower this weekend, with 850-mb
temperatures dropping from around 14-18C today to 2-6C by Sunday
morning. This will result in a chance of snow for the highest
elevations of the Black Hills and northeastern WY for the overnight
periods, especially late Saturday, Sunday, and Monday nights.

It looks like the final noteworthy short-wave will eject Sunday
night into Monday with the upper low moving northeast of the CWA
later on Tuesday. This will be followed by slowly building heights
and gradually warmer weather toward the end of next week.


.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 512 PM MDT Thu Sep 21 2017

VFR conditions can be expected this afternoon and tonight. Areas
will experience breezy northwesterly winds as the cold front
slowly moves east across the area.




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