Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 281712

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1112 AM MDT Fri Apr 28 2017

Issued at 956 AM MDT Fri Apr 28 2017

Current surface analysis shows low pressure over far southeast WY,
with high pressure over northern ND. Upper level analysis shows
elongated area of low pressure over southern WY, northern CO, and
northeast UT, slowly digging southward. Strong upper jet wraps
around the low from the Pacific NW to the Southern Plains. KUDX
radar shows snow over much of northeast WY into mainly far
southwest SD at this time, with the pcpn beginning to shift back
to the south and west now and starting to gradually decrease in
intensity. Current temps are mostly in the 30s, with some lower
40s over southeastern portions of the CWA. Winds are mostly from
the northeast at 10 to 20 mph.

Snowfall amounts since last night have been highly variable
across northeast WY and southwest SD. The highest totals appear to
have been from the Gillette area into parts of southern Campbell
County, where 6+ inches have been reported, with around 12 inches
in parts of the Gillette area. Localized areas of the southern
Black Hills into Fall River County have seen close to 6 inches of
snow as well. Otherwise, up to a few inches of snow has been seen
in other areas from Campbell County to the Black Hills and far
southwest SD.

Have updated forecast to adjust pops for the rest of today,
lowering or eliminating them through the afternoon across
southwest SD into far northeast WY. The main area of light
snowfall by early afternoon should be across Campbell County,
especially the southern half. Additional accumulations through the
afternoon look to be light, possibly another inch or two across
parts of Campbell County. Will likely cancel the winter wx
advisories across far southwest SD by Noon. May keep them going
across northeast WY through the early afternoon. Otherwise,
lowered high temps a bit across western areas.


.DISCUSSION...(Today Through Thursday)
Issued at 401 AM MDT Fri Apr 28 2017

Upper level analysis has weak cutoff low remaining over eastern
Wyoming, with strong jet rounding the base of the main trof into
the central Plains. Skies are cloudy or mostly cloudy across
northeast WY and southwest SD, with a steady stream of moisture
moving northwestward into the area. Temps are mostly in the 30s,
with some upper 20s over the higher Black Hills.

Today...Storm system will continue to spin over eastern WY
today, then track southeast into northeast CO late this afternoon
before getting swallowed up by stronger trof and low developing
across the Great Basin and Four Corners area. Latest medium range
models still showing some differences with regard to the eastern
and northern extent of pcpn shield across western South Dakota.
Will lean more towards the majority of models that have the main
precip band sinking south by late this afternoon. SREF is the
outlier with precip much further north than most. The heaviest
snow still looks to fall over southern Campbell County, with snow
gradually taper off in the afternoon. Snowfall amounts in southern
Campbell County look to mostly be in the 5 to 10 inch range, with
areas south and west of Wright possibly seeing higher amounts.
The advisory area should see 2 to 6 inches of snow, with locally
higher amounts possible, especially the further south and west
across those areas. Up to 2 or 3 inches of snow is possible across
the rest of the Black Hills into portions of far northeast WY and
toward portions of Oglala Lakota County. With the sharp gradient
in precip, temperatures will range widely from the mid 30s across
parts of Northeast Wyoming, to the lower 50s across northwest
South Dakota.

Snow will finally diminish across Northeast Wyoming this evening
with mostly cloudy skies remaining across much of the area.
Temperatures will fall into the mid 20s to lower 30s.

The weekend looks to be dry, but cool, as main trough and low
pressure system move east-northeast across the central and southern
plains and into the upper MS valley by Monday morning. A few showers
could clip far south central SD on the back side of the system
Sunday night. Highs will be in the mid 40s to mid 50s Saturday,
50s to around 60 on Sunday. The first half of next week still
looks to be unsettled with temps slightly below average. Daily
chances for showers are expected, especially for the afternoon and
evening hours, as a series of weak disturbances pass through on
the back side of the exiting trough. Latest longer range models
showing a nice warmup for late week, possibly into the first half
of the weekend as well, as a ridge finally moves over the area.


.AVIATION...(For the 18Z TAFS Through 18Z Saturday)
Issued At 1108 AM MDT Fri Apr 28 2017

Area of snow across northeastern Wyoming, the Black Hills area
and southwestern South Dakota will dissipate this afternoon.
Widespread IFR conditions expected with the snow. As the snow
ends, MVFR ceilings will remain across this area. The MVFR
ceilings will gradually improve to VFR by late evening. VFR
conditions expected through the period for the remainder of
western/northwestern South Dakota.


WY...Winter Storm Warning until 6 PM MDT this evening for WYZ055.

     Winter Weather Advisory until 6 PM MDT this evening for WYZ054.



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