Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 220437

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
937 PM MST Tue Feb 21 2017

.SHORT TERM...(This Evening Through Wednesday Night)
Issued at 250 PM MST Tue Feb 21 2017

Upper ridging across the central CONUS continues to slide eastward
into the upper Midwest. Over the Pac upper trough is moving
onshore with upper flow across the western CONUS and the CWA
transitioning to a more active southwesterly flow. In the low
levels...strong thermal ridge is crossing the northern Plains with
gusty W/SW flow across northeast WY and far western SD. Temps are in
the 60s across northeast WY into northwest SD...and low to mid 70s
across the rest of the western SD plains. Temps in the Black Hills
are in the 50s to low 60s at this time. Temps across some areas are
reaching near or breaking daily records for today. Winds have been
reaching near advisory criteria and occasionally gusting above
45mph...but most locations are staying under advisory so will end
the advisory for the foothills with the afternoon package. Winds
across northeast WY have dropped below warnings criteria, so will
also end headlines there. Rain showers are expected develop over the
next few hours ahead of a wave crossing WY/MT and a cold front
crossing the area. Showers will continue overnight with the frontal
passage with the Black Hills area seeing the best chance for
measurable QPF. Chances for precip will lower Wednesday as
subsidence takes over behind the departing wave. NW SD could see
some showers develop during the day into the evening as a backdoor
cold front slides into northwest to central SD. Temps will be cooler
tomorrow with highs in the upper 40s to upper 50s.

.LONG TERM...(Thursday Through Tuesday)
Issued at 250 PM MST Tue Feb 21 2017

Models continue to show a winter storm affecting the CWA Thursday
into Friday morning. GFS/ECMWF have both continued to show a
northward shift in the heaviest snow...which agrees with the GEM
solution from yesterday and today. This solution brings the track
of the 700mb low across southeast WY into the NE panhandle. This
brings the heaviest snow to southwest/south central SD into
NE...with the max sitting along the SD/NE border. The one outlier
is the NAM which is holding onto a more southerly track keeping
the bulk of snow over Nebraska. There is still uncertainty as to
what impacts the area will see given the lack of run to run
consistency within the models. But considering the agreement with
the 12z runs and this storm is only two days away...will go ahead
and issue a Winter Storm Watch for some portions of northeast
WY...the southern half of the Black Hills...and areas of the
western SD plains generally south of I-90. Snowfall amounts
generally appear to be in the 6 to 12 inch range with the heaviest
amounts probably closer to the Nebraska border in south central
SD. The Rapid City area seems to be on the fringe of the heavier
snowfall. Some guidance shows 6- 8" which others show around an
inch. At this time think it will be somewhere in the 3-5" range,
but will go with a watch in case model solutions shift slightly
northward. Snow will continue through Thursday night and end
across most areas Friday morning. Winds don`t seem to be an issue
with this system since it doesn`t really get wrapped up until it`s
east of our not anticipating a lot of blowing snow.
Heading into the weekend into early next week...with the main
upper flow across the region and several waves crossing the
area...could see occasional chances for snow. Will continue with
low pops across portions of the area. Temps will generally be in
the 30s to low 40s.


.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 934 PM MST Tue Feb 21 2017

Scattered showers will diminish late tonight. Local MVFR ceilings
with the showers. There will be some IFR visibility with snow
showers over the higher elevations of the Black Hills. VFR
conditions expected on Wednesday.


Issued at 250 PM MST Tue Feb 21 2017

River levels along the White River between Interior and the Missouri
River remain elevated due to the ice jams impacting the river this
past weekend. However, most of the ice is now out of the White
River, and the river has returned to below bankfull conditions.
Therefore the flood advisory has been cancelled.


SD...Winter Storm Watch from late Wednesday night through Friday
     morning for SDZ027-029-030-041-042-044-074.

     Winter Storm Watch from Thursday morning through Friday morning
     for SDZ026-028-031-043-046-047-049.

WY...Winter Storm Watch from late Wednesday night through Friday
     morning for WYZ055-058.



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