Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 181657
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1057 AM MDT Tue Apr 18 2017

.SHORT TERM...(Today Through Wednesday Night)
Issued at 350 AM MDT Tue Apr 18 2017

Current surface analysis shows low pressure over northeast SD
now, with cold front now through the CWA, just moving through
Winner in the last hour. Upper level analysis shows shortwave over
the central Dakotas, with the last of the shower and thunderstorm
activity now moving east of the forecast area. Skies have quickly
become mostly clear behind the pcpn with temps mostly in the
upper 30s and 40s. Gusty winds earlier behind the front have
diminished to less than 15 mph in most areas except for south
central SD.

Shortwave ridge will quickly cross the area this morning, bringing
fair conditions into the afternoon. Highs will be slightly above
average today, mostly in the 60s across the plains and 50s over the
Black Hills. The next system will approach quickly late today and
this evening, with showers and isolated thunderstorms developing
over northeast WY and the Black Hills late this afternoon, then
spreading east across most of the area tonight and continuing
through much of Wednesday in most areas. Models are and have been in
good agreement on general nature of this system, but still some
slight differences on track and where the heavier pcpn will fall.
GFS and NAM are a bit further south than the EC, which is weaker and
faster with the system. However, all of them focus a good amount of
pcpn across the Black Hills area and eastward onto the western SD
plains later tonight into Wednesday, where the best forcing and
frontogenesis are forecast. An inch or more of rainfall looks likely
across a good portion of this area, including parts of northeast WY
as well, with some locations close to 2 inches if the system leans
toward the stronger solutions. To the south and north of these
areas, amounts will generally taper off, with the least amounts of
pcpn at this time looking to be across far southern SD and far
northwest SD near the ND border. Any shifts to the north or south
will greatly affect amounts in these areas, but most of the CWA
should see beneficial rainfall from this system. Across the higher
elevations of the Black Hills, mainly near or above 6000 ft,
temperatures could become cold enough late tonight and Wednesday
morning for accumulating snowfall. Several inches or more is
certainly possible across the highest elevations of the northern and
central Black Hills, especially from Deerfield to O`Neil Pass to
Terry Peak, if pcpn changes over early enough later tonight.

Highs on Wednesday will be on the cool side, 40s and lower 50s with
some upper 30s across the highest Black Hills. Rain will begin to
taper off from west to east late Wednesday afternoon and evening as
the system exits. Clouds will only slowly decrease overnight with
lows back into the 30s.

.LONG TERM...(Thursday Through Monday)
Issued at 350 AM MDT Tue Apr 18 2017

A brief break from the unsettled weather can be expected on
Thursday before the next system digs southeast from the Northern
Rockies to the Central Plains Thursday night and Friday. Latest
models, except for the GEM, have persisted with the more northward
track. This system will likely bring a good chance for rain to
northeast WY and southwest SD, with chances tapering off rather
quickly to the northeast. The higher Black Hills could see
additional light snow late Thursday night into Friday morning if
pcpn makes it that far east. This system will exit the region
Friday night, but additional energy in active flow could bring
some showers across the area through Saturday. Dry and warm
weather is still anticipated for Sunday before another series of
disturbances bring chances for showers Sunday night into early
next week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1055 AM MDT Tue Apr 18 2017

A storm system will approach from the west tonight spreading
showers into the area. TSRA possible across the south. Mainly VFR
conditions this afternoon will deteriorate tonight with widespread
MVFR CIGS developing; local LIFR/IFR conditions will occur with
the heaviest precipitation and near the Black Hills where some
snow will occur late.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

SHORT TERM...26
LONG TERM...26
AVIATION...Johnson



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