Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 161720

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1120 AM MDT Mon Apr 16 2018

.DISCUSSION...(Today Through Sunday)
Issued at 255 AM MDT Mon Apr 16 2018

Current surface analysis shows low pressure over central MT, with
frontal boundary nearly stationary from southeast MT to eastern
CO. Upper level analysis shows ridge axis over the high plains,
with low pressure systems along the Pacific NW coast and over the
western Great Lakes. Skies are clear across much of the area, with
some low clouds trying to clip far south central SD and a few mid
level clouds over far northwest SD. Temps range from the teens
over south central SD to the 30s over northeast WY.

Frontal boundary to the west will edge eastward into northeast WY
today, with high pressure to the east of the region. Tightening
pressure gradient between low pressure over MT and high pressure to
the east of the region will produce breezy to windy south to
southeast winds today. The strongest winds look to be across far
northwest SD. A wide range of temperatures can be expected across
the area again, with highs in the upper 30s across south central SD
to the lower 70s across Campbell County WY. Temperatures will
continue to be tricky across snow covered areas of western SD, but
milder air aloft should allow for warmer temperatures than

The next system will approach the area late tonight and Tuesday
morning as low pressure aloft over the Pacific NW moves into
southwest Canada and ejects a shortwave trough across the Northern
Rockies into the Northern Plains. Low pressure and accompanying cold
front will also move southeast across the region on Tuesday. Areas
of rain and snow will develop across the area Tuesday into Tuesday
night, with gusty northwest winds also developing behind the front.
Pcpn on Tuesday will mostly be on the lighter side, but some areas
will receive a tenth of an inch or more of pcpn, with light snow
amounts also possible, especially across the Black Hills. As the
trough moves east of the region Tuesday night, it is expected to
intensify over eastern portions of SD and NE. Some enhanced pcpn and
snowfall is possible over south central SD Tuesday night, with the
heavier snowfall east-southeast of the forecast area. Amounts up to
a few inches are possible by Wednesday morning, especially in the
Winner area.

The rest of Wednesday through the day on Thursday will be dry as
another shortwave ridge moves across the region. Temperatures look
to remain below average through the rest of the week, as the next
strong system digs southeast across the western US late week. Medium
range models still showing differences with regard to track and
intensity, with the EC and Canadian tracking it further south across
the Rockies and Plains than the GFS. The brunt of the system looks
like it will stay south of the forecast area. However, shortwave
energy lifting northeast of the system from late Thursday night into
Friday night could bring some rain and snow to at least parts of
northeast WY and much of southern SD. Temperatures look to be
marginal for snowfall on the SD plains, but some accumulations
certainly look possible across the higher elevations further west. A
ridge behind the exiting system should bring drier weather and more
seasonable temperatures by Sunday.


.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1116 AM MDT Mon Apr 16 2018

VFR conditions will continue through this evening with gusty
south winds across much of the area. Stratus/patchy fog may
develop across the plains of western South Dakota tonight. Low
confidence in this stratus affecting the KRAP terminal...but did
throw some lower scattered clouds overnight. Cold front moves into
northeast Wyoming/northwest South Dakota Tuesday morning with
MVFR/IFR conditions with scattered rain/snow.


Issued At 255 AM MDT Mon Apr 16 2018

A period of elevated fire wx conditions is likely during the mid
to late afternoon across fire zones 259 and 297 in WY. Breezy
southerly winds of 15 to 25 mph with gusts to 35 mph can be
expected with relative humidities falling to 15 to 20 percent,
mainly across western and southern portions of Campbell county.




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