Area Forecast Discussion
Issued by NWS Rapid City, SD

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127
FXUS63 KUNR 201104
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
504 AM MDT Thu Sep 20 2018

.DISCUSSION...(Today Through Wednesday)
Issued at 144 AM MDT Thu Sep 20 2018

Water vapor shows upper trof working into the Northern Rockies
with broad large scale ascent extending eastward into the
Northern Plains. Monsoonal moisture plume extends from Mexico
through the Four Corners and north/northeast through the Northern
Plains. At the surface, broad northeast boundary layer flow
continues across the region. Widespread showers (and isolated
storms) and drizzle cover the entire CWFA.

It will remain very wet across the area this morning. Some
elevated instability will produce a few thunderstorms, but most of
the precipitation will fall in the form of showers/drizzle. Drier
air will then begin to work in from the west/southwest later
today as upper trof axis pushes into the Northern Plains and the
monsoonal moisture plume shifts east. The majority of
precipitation should end by this evening, with only a few
lingering showers in northwest SD. Breezy northwest winds expected
by tonight behind surface trof. With temps falling into the 30s
tonight from northeast WY into northwest SD, some frost is
not out of the question if the post frontal northwest winds
become light enough towards morning. Will let day shift
forecasters examine this further to determine if frost needs to be
added to the forecast.

Dry and warmer weather expected Friday through the weekend with
flat upper ridge overhead in between upper trofs. Next upper trof
then brings cooler and more unsettled weather for early/mid next
week. Longer range guidance quite consistent with deep long wave
trof developing over the central/eastern CONUS by late week which
could bring us even colder weather for the tail end of the
forecast period and beyond.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Friday Morning)
Issued At 454 AM MDT Thu Sep 20 2018

Widespread MVFR/IFR conditions in fog and drizzle will continue
this morning, with LIFR conditions around the Black Hills. Showers
and isolated thunderstorms will also continue today, gradually
diminishing this afternoon and evening. MVFR ceilings could
persist across northwestern SD through tonight, but VFR conditions
are expected most places by 03Z or so.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION...Johnson
AVIATION...Pojorlie



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