Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 170510

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1110 PM MDT Tue May 16 2017

.DISCUSSION...(This Evening Through Tuesday)
Issued at 153 PM MDT Tue May 16 2017

Latest upper analysis shows another upper low moving onshore into
the pacific northwest while the previous upper low gradually
weakens over the four corners region. As the week progresses, the
four corners system will move out to the northeast as it deepens
again over central plains and the pacific Northwest system will
continue to drop southward, reaching the four corners area by
Thursday morning. This will result in the unsettled weather
continuing through the rest of the work week, with a noticeable
cooldown for the second half of the week and some snow possible
over the higher elevations of the Black Hills and northeastern WY
late in the week.

At the surface this afternoon a secondary sfc cold front has
pushed southward across most of the forecast area today and is
currently oriented W-E across parts of southwestern and south
central south Dakota, continuing to move southward. MLCAPE to the
south of the front ranges from 1000-1500J/KG and the CIN has
eroded. Are starting to see some convective development near the
boundary again this aftn. Latest WV images show another upper
shortwave heading northeastward toward the forecast area so expect
to see an increase in coverage and strength of the convection
again through the rest of the afternoon. The best chance for any
severe thunderstorm development this afternoon and evening will be
south of the sfc boundary, over swrn and south central SD with
the strongest storms most likely nern the SD-NEB border.

Wednesday could be a relatively wet day for some areas as the
first upper low moves into sern SD and the second upper low moves
into srn Idaho. Cool and moist easterly upslope flow and energy
ahead of low to the west could bring fairly widespread light to
moderate rainfall. A few thunderstorms are also possible. High temps
will be on the cool side, highs mostly in the 50s, some 40s
across the BH. As the upper low remains to the southwest of the
area through late week, good chances for pcpn will persist
through at least Thursday and across at least parts of the area
into Friday as a series of upper shortwaves affect the region in
southwesterly flow aloft. Temps will likely be cold enough for
some snow across the higher elevations of the Black Hills and
northeastern WY, especially during the overnight and morning
hours on Thursday and Friday. Expecting mainly light accumulations
at this time, but timing and track of various disturbances
rotating through the area could change things a bit.

Overnight temps late in the week will approach freezing across some
of the plains, especially Thursday night and Friday night, with some
frost possible. Still looks like drier weather will return for the
weekend, with a gradual warming trend into early next week. Chances
for showers and storms will likely return by the end of the weekend
and especially early next week.


.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1105 PM MDT Tue May 16 2017

A few showers/isolated thunderstorms will linger overnight, mainly
over southwest and south central South Dakota. Widespread
MVFR/IFR ceilings will develop overnight with some LIFR
conditions around the Black Hills. IFR ceilings will remain across
portions of northeast Wyoming, the Black Hills, and southwestern
South Dakota through Wednesday morning, with some improvement late
morning/early afternoon. Coverage of showers will increase
Wednesday across northeast Wyoming into southwest South Dakota.




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