Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 220442

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1042 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 06Z TAFS Through 06Z Thursday Night)
Issued At 1041 PM MDT Wed Sep 21 2016

VFR to IFR conditions currently ongoing in the region. Model
soundings show cigs/vis deteriorating through the overnight hours
into tomorrow morning before gradually improving tomorrow
afternoon. Isolated showers are possible in northeastern WY and
parts of Western SD during the overnight hours.




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