Area Forecast Discussion
Issued by NWS Rapid City, SD

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826
FXUS63 KUNR 201014
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
314 AM MST Mon Nov 20 2017

.DISCUSSION...(Today Through Sunday)
Issued at 250 AM MST Mon Nov 20 2017

Water vapor shows large ridge over the western CONUS, with a
trof extending from Alta southwestward to just offshore the Pac
NW. At the surface, low center is over southern Sask with broad
trof over the Northern Plains, and associated cold front over
southern Alta. Widespread mid and high level warm advection clouds
spilling into the Northern Plains.

Thickness ridge is expected to peak over the cwfa today, with
gusty w/nw boundary layer flow pushing temps into the 60s east of
the Black Hills. Minimum rh`s this afternoon will drop well down
into the 20s, with some teens east of the Black Hills creating
some fire wx concerns.

Cold front is then expected to drop into the cwfa late this
afternoon into tonight. Strong cold advection combined with short
wave at the base of the upper level will create a band of light
pcpn from NE WY through the Black Hills into SW SD tonight. Could
see some light snow accumulations by morning, especially in higher
elevations, but there is not much moisture to work with so nothing
significant expected.

Any pcpn will taper off early Tuesday, with some gusty northwest
winds continuing through the day and highs only in the 30s to
lower 40s.

Upper ridge quickly rebuilds across the western CONUS and leads to
dry and very mild conditions mid to late week. The warmest day
looks to be Thanksgiving where it`s possible a few areas east of
the Black Hills reach close to 70 degrees.

Next upper trof and associated cold front will move through on
Friday with slightly cooler weather through the weekend. Could be
just a bit of light pcpn on Friday with the cold frontal passage,
but moisture once again will be very limited.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Tuesday Morning)
Issued At 250 AM MST Mon Nov 20 2017

VFR conditions will continue through this afternoon. Gusty west
to northwest winds will be the main concern through the first half
of the TAF period as a cold front approaches and crosses the
region. Ceilings will begin to lower late in the afternoon and
evening, with some MVFR ceilings possibly developing after 00z
Tuesday. A few showers may also occur 00-06z Tuesday at GCC, but
confidence is too low to include in the TAF at this time.

&&

.FIRE WEATHER...
Issued At 250 AM MST Mon Nov 20 2017

Very mild and dry conditions expected today, with some gusty west
to northwest winds ahead of an approaching cold front. Relative
humidities will drop into the 20s, with some teens possible east
of the Black Hills. A period of elevated fire wx conditions is
likely across a good portion of the forecast area this afternoon,
with high to very high grassland fire danger across the western
and south central SD plains.

Cooler conditions expected on Tuesday behind the cold front, but
very mild and dry conditions will return for mid to late week with
elevated fire wx conditions at times.

&&

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

&&

$$

DISCUSSION...Johnson
AVIATION...13



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