Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 180147

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

Issued at 744 PM MDT Sun Sep 17 2017

Weak convection, on the leading edge of short wave moving eastward
out of WY, has developed a little further north into the area this
evening. Have adjusted pops a bit further north. Expect most
activity to shift east of our zones by or shortly after midnight.


.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 00Z TAFS Through 00Z Monday Evening)
Issued At 747 PM MDT Sun Sep 17 2017

VFR conditions are expected through the period. A few high based
-shra/-tsra across southwest SD will shift east out of the area by
 or shortly after midnight. No pcpn expected at either KRAP or


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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