Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 171907

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
107 PM MDT Sun Sep 17 2017

.DISCUSSION...(This Evening Through Sunday)
Issued at 106 PM MDT Sun Sep 17 2017

Water vapor images showed a trough over central MT/WY moving
toward the CWA. Although moisture is limited with this system,
surface observations indicated low-level moisture returning over
southwestern SD. Strong southerly flow and surface pressure falls
will lead to further destabilization and moisture return through
this afternoon/evening. Therefore, expect scattered showers and
thunderstorms to develop by late this afternoon over southwestern
SD and then move across southern SD this evening, which the CAMs
have basically converged on. Given the weak instability do not
expect any severe storms.

Monday will be dry and warmer than today as the 850-mb temperatures
rise to the lower 20s Celsius. South winds could become a bit breezy
late in the day as a low-level jet develops, continuing through
Monday night. Models then agree well on a strong trough approaching
the CWA on Tuesday. However, they differ on the timing of a cold
front that ultimately will move through the CWA by Tuesday night.
Scattered showers and a few thunderstorms should result behind the
front over much of the CWA Tuesday afternoon and evening, although
precipitation amounts generally will be light.

Wednesday will be another dry day as a short-wave ridge moves across
the CWA. Unsettled weather is then expected for the rest of the week
as a big trough becomes established across the West, and southwest
flow aloft prevails over the CWA. Best rainfall chances appear to
be on Friday and Saturday. Temperatures also will be at least 10
degrees below average.


.AVIATION...(For the 18Z TAFS Through 18Z Monday)
Issued At 1127 AM MDT Sun Sep 17 2017

Scattered low clouds around the Black Hills area will continue to
dissipate over the next couple hours. MVFR conditions will be
possible in showers/storms today across southwestern into west
central SD. Otherwise, VFR conditions are expected through the


Issued At 106 PM MDT Sun Sep 17 2017

Highs Monday will be in the upper 70s to lower 80s with afternoon
relative humidities falling to 15-20 percent across northeastern
WY and much of southwestern SD. The winds, however, should only
reach 10-25 mph, with the windiest conditions across Campbell
County. Thus, the weather will be somewhat conducive to wildfire,
although not critical. A cold front will move across the area
Tuesday, bringing gusty northwest winds.




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