Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 212321

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
521 PM MDT Wed Sep 21 2016

.SHORT TERM...(This Evening Through Thursday Night)
Issued at 150 PM MDT Wed Sep 21 2016

Upper analysis shows a deepening upper low/trough over the Pacific
northwest with weak ridging currently over the forecast area.
Latest sfc analysis shows numerous weak boundaries across the
forecast area this afternoon. The main sfc feature is a nw-se
oriented trough across northeastern Wyoming into southwestern
South Dakota.

Tonight through Thursday, the upper low will continue to deepen
over the pacific northwest tonight, moving into UT Thursday, then
ejecting quickly northward on Thursday night. A surface low will
persist along a frontal boundary from WY into CO and NEB as the
edge of a 1026mb sfc high slips southward from Canada into nrn
MT,ND and MN. Persistent easterly boundary layer flow is expected
with increasing moisture given theta-e advection and converging
T/Td. Expect widespread stratus by tonight with areas of drizzle
and fog at times, especially late tonight and Thursday morning
along the eastern slopes of the Blkhls. Upper forcing will
increase ahead of the approaching upper low with southwest flow
aloft. Shower and embedded thunderstorm chances increase overnight
and especially Thursday night ahead of upper low with relatively
high pops warranted. Temperatures will be around 10F cooler than
average on Thursday.

.LONG TERM...(Friday Through Wednesday)
Issued at 150 PM MDT Wed Sep 21 2016

A strong upper low over the Great Basin will slide NE
toward the nrn Plains for the end of the week into the weekend.
Strong warm air advection across wrn SD will bring weak instability
and decent shear to the SD plains...with chances of elevated
showers/storms to the CWA. Models then show dry slotting moving into
the CWA Saturday with colder air pushing in. There are some big
changes in both the ECM/GFS heading toward midweek. Both now show a
strong upper low stalling across the region bringing more cool and
wet weather. Will wait to see better run to run consistency before
considering significant increases in pops.


.AVIATION...(For the 00Z TAFS Through 00Z Thursday Evening)
Issued At 518 PM MDT Wed Sep 21 2016

MVFR/IFR conditions are expected to redevelop this evening
through the night especially as areas of fog redevelops. lifr
conds will be possible late tonight in the lee of the black hills
in drizzle and fog. conditions will trend mvfr most areas thurs
morning and continue through much of Thursday. There is a chance
of showers across ne WY and portions of wrn SD.




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