Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 182015
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
215 PM MDT Sat Mar 18 2017

.SHORT TERM...(This Evening Through Sunday Night)
Issued at 211 PM MDT Sat Mar 18 2017

20z surface analysis had low over central AB with warm front
extending south into western NE. Decent gradient along warm front
with 2-4mb/3hr pressure falls supporting gusty winds where
boundary layer is fully mixed - out of the southwest in northeast
WY and out of the southeast from northwest into south central SD.
Upper ridge over the northern plains per latest water vapour
matinee.

Tonight, upper ridge shifts east as thermal ridge peaks under
southwest / downslope flow behind warm front. AB low moves east,
which pushes pre-frontal trough into the CWA. Temperatures tonight
tricky with readings struggling into the 40s where the wind stays up
and dropping into the 30s elsewhere. Gusty winds over the higher
terrain at times given low level jet development over western SD.

Sunday, shortwave moves from western WY into ND pushing the pre-
frontal trough into the southern half of the CWA where it will stall
as it becomes parallel to upper level flow. Cold front develops over
MT/ND and shifts south into trough by evening, which is in response
to high building out of southwest Canada into the northern plains.
Combination of shortwave and frontal boundary may be focus for -SHRA
in the afternoon and -SHRASN Sunday night over the western two-
thirds of the CWA. Perhaps a rumble of thunder over the Black Hills
given 100J/kg SBCAPE.

.LONG TERM...(Monday Through Saturday)
Issued at 211 PM MDT Sat Mar 18 2017

Monday into Tuesday morning, aforementioned frontal boundary
remains stalled near the SD/NE border and then west into southwest
WY. Shortwave energy moves from NV into WY under right entrance
region of departing 120kt upper level jet over the northern
plains. Narrow band of lift along baroclinic zone behind frontal
boundary will link up with synoptic support to produce a band of
-RA changing to -SN later Monday into Tuesday morning, especially
from 06z-18z Tuesday. Latest guidance is further north than
previous runs. Shifted higher PoPs north with potential for 1-2"
of snow from the Black Hills to south central SD. Temperatures
will be tricky given cloud cover, cold air advection, and
precipitation.

Tuesday afternoon into Wednesday, progressive upper ridge allows for
warmer temperatures Wednesday, but some precipitation still possible
given southwest aloft developing ahead of next upper trough over the
Rockies.

Thursday and Friday, significant differences in operational models
with evolution of upper trough. GFS progressive with upper low over
IA. Canadian slower, but weaker with split energy. ECMWF shows
split energy with much stronger upper low in the southern plains,
passing well south to be of any consequence. Confidence low for
sensible weather for this time period.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 211 PM MDT Sat Mar 18 2017

VFR conditions will continue through Sunday morning. Gusty
southerly winds will continue through tonight over northeast WY. A
trough will push into the region tonight, supporting LLWS over
western SD where boundary layer decoupling occurs. Gusty southwest
to west winds may occur on the eastern slopes of the Black Hills
later tonight.

&&

.FIRE WEATHER...
Issued At 211 PM MDT Sat Mar 18 2017

Critical to near critical fire weather conditions will end early
this evening over northeast WY into southwest SD. Low relative
humidities and unseasonably warm temperatures are expected again
Sunday, but the best support for red flag conditions will remain
south of the area.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...Red Flag Warning until 7 PM MDT this evening for WYZ259-297.

&&

$$

SHORT TERM...Helgeson
LONG TERM...Helgeson
AVIATION...Helgeson
FIRE WEATHER...Helgeson



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