Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 271717
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1117 AM MDT Thu Apr 27 2017

.UPDATE...
Issued at 1026 AM MDT Thu Apr 27 2017

Current surface analysis shows low pressure over western WY and
southeast CO, with frontal boundary stretching between the two
areas. Upper level analysis shows cutoff low remaining over
southwest Canada, with strong jet digging southeastward from the
Pacific NW to the southern plains. Strengthening shortwave energy
noted on water vapor imagery across the northern into central
Rockies. Skies are cloudy or mostly cloudy across much of the
area with temps in the mid 30s to mid 40s. Regional radars showing
showers from south central MT to southeast WY and the Neb
panhandle. A few showers look to be clipping southern parts of
northeast WY, while isolated showers have started to develop over
western portions of the Black Hills.

Mostly minor changes made to the forecast for the rest of today.
Lowered temps a couple of degrees in some areas, mainly southern
and western portions of the CWA, and adjusted pops over western
and southern portions of the CWA. Also raised cloud cover over
eastern areas as low clouds have backed into those areas this
morning. 12Z model runs that have come in so far have not showed
much change to track and timing of upcoming system and where
heavier pcpn and snowfall are expected, so no changes to the
forecast for tonight and Friday for now.

&&

.DISCUSSION...(Today Through Wednesday)
Issued at 358 AM MDT Thu Apr 27 2017

Upper level analysis has large trof across the central CONUS with
weak shortwave ridge embedded in the larger trof. Skies are mostly
cloudy across the Northern Plains with the exception of a sliver
of clear skies across the western Dakotas into central Nebraska.
At the surface, Canadian high pressure resides across the Dakotas,
with low pressure centered across central Wyoming. Temperatures at
4am are in the 20s to lower 30s, and winds are light and variable.

Today...The next spring storm system will begin to impact western
portions of the area, with chances for rain and snow increasing
across northeast WY into southwest SD this morning. Most of the
pcpn should be in the form of rain later in the day as slightly
milder air pushes in. Highs will be in the 40s and lower 50s,
warmest over eastern areas where there will be more sun.

Tonight...Latest model consensus still showing potent system
shifting into eastern Wyoming and spreading into southwestern
South Dakota early this evening. Rain will quickly change over to
snow across northeast WY and the Black Hills this evening as
temperatures cool. With high pressure over the central Dakotas,
most of the precip should be confined to the Black Hills area and
west. Snowfall amounts look to be on the lighter side on the
eastern fringes, with around 1 to 3 inches across the Black Hills.
A little more snow is expected south and west of the Black Hills,
with accumulations up to 6 inches across parts of far western Fall
River County, Weston County, and areas west of Gillette. However,
across southern Campbell County where the heaviest pcpn is
forecast, 6 to 8 inches of snow is possible, especially across
the higher elevations. A Winter Storm Warning has been issued for
southern Campbell County through Friday afternoon, with Winter
Weather Advisories posted for northern Campbell, Weston, and Fall
River Counties. Pcpn will dissipate and shift south of the area
Friday night as system moves into the Central Plains. Lows tonight
will be in the 20s to lower 30s.

The weekend looks mainly dry, but remaining cool, as large trof
lingers over the region. Will see temperatures possibly
approaching average early next week, but unsettled weather will
return for at least the first half of the week. Active northwest
flow on the back side of the trough will bring several
disturbances across the area, with daily chances for showers in
most areas. The bulk of the activity should come during the
afternoon and evening hours.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Friday)
Issued At 1112 AM MDT Thu Apr 27 2017

MVFR ceilings across western into central South Dakota will
gradually improve this afternoon on the plains, with the ceilings
persisting in the vicinity of the Black Hills. Area of
precipitation develops across northeast Wyoming into southwest
South Dakota this afternoon and continues thorugh Friday morning.
Temperatures will be cold enough for snow, especially tonight and
Friday morning. Widespread IFR ceilings and visibility with the
snow.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from 6 PM this evening to 6 PM MDT
     Friday for SDZ041.

WY...Winter Storm Warning from 6 PM this evening to 6 PM MDT Friday
     for WYZ055.

     Winter Weather Advisory from 6 PM this evening to 6 PM MDT
     Friday for WYZ054-058.

&&

$$

Update...26
DISCUSSION...15
AVIATION...7



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