Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 122311

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
511 PM MDT Tue Sep 12 2017

.DISCUSSION...(This Evening Through Tuesday)
Issued at 240 PM MDT Tue Sep 12 2017

Water vapor imagery shows compact upper low centered across western
SD pushing E/NE. This system has initiated convection across the
Black Hills which has since shifted eastward into the western SD
plains. With PWATs at 150% of normal...these storms produced
rainfall rates exceeding 3 inches an hour. Activity tonight will
continue to slide eastward as the upper low moves into the central
and eastern Dakotas overnight. Drier weather will return after
midnight tonight. Flat upper ridging will continue across the region
through Wednesday with the next upper wave bringing additional
chances for storms Wed afternoon and evening. PWATs will be at 125-
150% of normal so some of the stronger storms could have locally
heavy rainfall. Like today, a few storms could have small hail and
gusty winds, but severe weather is not expected. Highs will reach
the mid 80s to mid 90s.

A broad upper trough will move into the Pac NW coast Thursday and
cross the western CONUS Friday and Saturday. This will setup a very
active pattern for the region for the end of the week as a synoptic
scale storm system strengthens over the northern High Plains. The
surface low will track somewhere across Nebraska into South Dakota
with wrap around precip affecting much of the region from Thursday
night through Saturday. Colder air will filter into the region
Friday through the weekend with temperatures dropping off
significantly. Temperatures will cool off through the day
Friday...then be limited to the mid 50s to upper 60s Saturday. Drier
air moves back in early next week with temps slowly recovering.


.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 508 PM MDT Tue Sep 12 2017

Mainly VFR conditions expected through period. Isolated -TSRA over
northeast WY/southwest SD will end early this evening. Scattered
TSRA with local MVFR conditions over southwest into central SD
will end by 06z. Isolated to scattered TSRA will develop over the
region Wednesday afternoon.




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