Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 230520

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1020 PM MST Wed Feb 22 2017

.SHORT TERM...(This Evening Through Thursday Night)
Issued at 239 PM MST Wed Feb 22 2017

Upper analysis shows a weak wave moving through the northern
plains, and a trough pushing in over the west coast. Skies are
mostly cloudy over northwestern SD, with some light rain showers
around the northern Hills. Farther south, skies are mostly sunny.
Somewhat tight pressure gradient behind the surface low is keeping
northwest winds breezy across the CWA. Temps are rising into the
40s and 40s.

Low pressure will deepen tonight as trough swings over the Rockies.
With the 700 mb low over southern WY by 12Z, snow will begin pushing
into northeastern WY and southwestern SD early Thursday morning.
Cold air will wrap into the area with easterly winds, and snow will
expand northward across much of SD as the low moves across NE. Best
frontogenesis still looks to be along the SD/NE border, with the
higher amounts expected there. Easterly winds on Thursday will aid
in upslope snow over the eastern foothills. The tricky part will be
the northern extent of the greater snow amounts. The 12Z NAM has
come in with a slightly stronger low with a more northerly track,
bringing the higher amounts of snow northward. However...the
GFS/EC/Canadian are staying with the more southerly track, and the
12Z EC is even farther south than the 00Z run. Thinking the southern
half of the CWA will see 6 or more inches of snow, with more towards
the NE border and especially across south central SD where more than
a foot of snow could fall. Warnings have been issued for tonight
into Friday, with some advisory criteria snow possible across far
northeastern WY. Did not issue an advisory north of the SD warnings
because of the southerly trend of most of the models and the sharp
cutoff in the snowfall grids, but later shifts can reassess whether
to add advisories to the north.

.LONG TERM...(Friday Through Wednesday)
Issued at 239 PM MST Wed Feb 22 2017

Snow will begin to taper off across the area Friday morning as
low pressure moves quickly into the upper midwest. Models are
showing stronger winds than previously across south central SD
behind the low on Friday. The stronger NAM shows the potential for
blizzard-strength winds, but since this model seems to be the
outlier, just nudged winds up a bit and extended the Winter Storm
Warning through Friday afternoon for blowing snow.

Mostly dry weather is expected over the weekend and Monday as drier
northwest flow is in place. Weak disturbances will bring clouds and
the possibility for snow showers at times, mainly across far
northeast WY, the Black Hills, and northwest SD. Temperatures will
generally be slightly below average Friday into next week, with
highs mostly in the mid 20s to mid 30s. The next upper level system
progged to impact the region will be Monday night and Tuesday. At
this point the Canadian is the only model giving the CWA any
significant precip; the ECMWF and GFS have a weaker system with less


.AVIATION...(For the 06Z TAFS Through 06Z Thursday Night)
Issued At 1018 PM MST Wed Feb 22 2017

MVFR ceilings will deteriorate quickly as the next storm system
begins to impact the area overnight, with snow moving into
northeast WY and southwest SD. MVFR/IFR conditions will develop
across these areas, with areas of LIFR conditions expected by 12Z,
especially across southern parts of northeast WY and far
southwest SD. LIFR conditions in snow will persist through much
of the day on Thursday.


SD...Winter Storm Warning until 11 AM MST Friday for SDZ027-029-030-

     Winter Storm Warning from 6 AM Thursday to 6 PM CST Friday for

     Winter Storm Warning from 5 AM Thursday to 11 AM MST Friday for

WY...Winter Weather Advisory from 5 AM Thursday to 11 AM MST Friday
     for WYZ054-056-057.

     Winter Storm Warning until 11 AM MST Friday for WYZ055-058.



SHORT TERM...Pojorlie
LONG TERM...Pojorlie
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