Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 192031

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
231 PM MDT Wed Sep 19 2018

.DISCUSSION...(This Evening Through Wednesday)
Issued at 231 PM MDT Wed Sep 19 2018

Stationary front continues to reside over the region with ample
deep moisture just south of the front. Stronger/deeper impulse
will eject out of the Rockies tonight and support another round of
showers and few storms. Heaviest precip is expected across
scentral SD, closer to the deeper moisture in place, along with
growing elevated instability. An isolated severe TS or two will be
possible in extreme eastern scentral SD with large hail the main
threat. Further west, moist NE upslope flow is supporting moderate
to heavy drizzle on the east side of the Black Hills with dry
downslope flow in parts of NE WY. Drizzle and fog will continue
this evening until showers develop overnight and scour some of the
ll moisture. Best chance for showers in western areas will be
across NW SD late tonight as the upper trough pushes east. Sfc dry
trough will push through the far SW FA Thur, supporting breezy NW
winds with some clearing there. This will be the warmest spot in
the FA with temps in the low 70s expected from NE WY into far SW
SD. Further NE, cool moist easterly flow will dominate supporting
a very cool day there, esp across far NW SD. A few diurnal showers
will be possible in the SW third where things mix out given
lingering cold pool aloft. Things will dry out by Friday as
shortwave ridging commences with a dry and mild weekend expected.
Another upper trough will push through Sunday into Monday with a
cooling trend for the early part of next week. This system looks
to be mostly dry with PAC moisture being the main moisture source,
with only low pops in the forecast at this time, mainly across
the western third including the northern Black Hills.

Semi-blocking pattern is favored toward the middle of next week,
which would support a local pattern change. This would favor mid
CONUS toughing with long trajectory northerly flow bringing much
cooler conds to the region, bringing the potential for a
widespread frost. If current models trends favoring massive
ridging across the north Atlantic verify, the cool pattern could
linger well into next weekend with even some snow possible in the
Black Hills.


.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1130 AM MDT Wed Sep 19 2018

Moist easterly upslope flow will result in widespread IFR
conditions today and tonight, with LIFR conditions for the Black
Hills. Scattered rain showers will continue into Thursday
morning. Conditions will begin to improve across parts of
Northeast Wyoming late Thursday morning.




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