Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 232309

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
509 PM MDT Sun Sep 23 2018

.DISCUSSION...(This Evening Through Sunday)
Issued at 153 PM MDT Sun Sep 23 2018

Upper trough is pushing east across the NW CONUS supporting a sfc
cyclone across eastern WY. A backdoor cold front has settled
south into the FA, with low clouds and patchy fog north of the
front. There is quite the temp spread across the FA this afternoon
due to this feature, with 40s and 50s to the NE and 70s and 80s
to the SW. Gusty SW flow will continue across the far SW this
afternoon, with the cold front eventually picking up speed pushing
south this evening. Lead forcing per the upper tough and an
associated jet streak will support increasing lift for high based
showers tonight, with better organization later tonight across the
far SE when better moisture advects into the system. This will
support sct showers, best coverage over scentral SD. Convective
showers under the upper trough are expected Monday afternoon and
evening from NE WY into far western SD. The best chances will be
over the Black Hills where the cold pool aloft will support the
best instability. Some thunder will also be possible. Secondary
cold front will push through the area Monday night. CAA will
continue into Tue on the backside of the upper trough supporting a
very cool day. Dry air, clear skies, and the sfc ridge advecting
over the region will support a good chance of frost most places
Tues night. Have added a mention of frost then.

Mean central NOAM troughing is then expected through the end of
the week as cold air continues to pile up across interior Canada.
This will likely support a baroclinic zone over the region with
the colder air (per NE flow) banking up against the Rockies. This
could support warm breezy conds across the far SW FA, with cold
cloudy conds to the NE. Although forecast models have backed off
the really cold air progged a few days ago, it still looks much
cooler for most of the region toward next weekend. Hence,
continued to side with numbers toward the cool side of the 50
percentile. As for precip, mean jet stream progs would favor the
bulk of activity to the north of the FA.


.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 504 PM MDT Sun Sep 23 2018

A back door cold front will exit the area to the south early this
evening. MVFR/IFR CIGS behind it across northwest SD will likely
persist most of the night in some form, but confidence is low as
winds should slowly become northwest and allow some improvement. A
disturbance will bring scattered rain showers overnight into early
Monday morning with another disturbance bring showers and isolated
thunderstorms Monday afternoon. MVFR conditions may occur with any
of the precipitation. Finally, LIFR fog may develop overnight into
Monday morning near the MT/ND border and possibly at the
intersecting terrain of the Black Hills.


Issued At 153 PM MDT Sun Sep 23 2018

Breezy SW winds will continue ahead of a cold front this
afternoon from far southern Campbell county into SW SD. RH`s ahead
of the front will be tin the 10 to 15 percent range. Will
continue the red flag warning in place.


SD...Red Flag Warning until 7 PM MDT this evening for SDZ262-263.

WY...Red Flag Warning until 7 PM MDT this evening for WYZ259-298.



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