Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 182319
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
519 PM MDT Fri May 18 2018

.DISCUSSION...(This Evening Through Friday)
Issued at 116 PM MDT Fri May 18 2018

Water vapor shows large upper trof covering much of the western
CONUS with an upper low over southwest WY. Cool/moist boundary
layer flow is from the north/northeast across northeast WY and
western SD behind main surface trof, and satellite imagery shows a
secondary low over northwest SD with frontal boundary westward
along the MT/WY border. Some -shra beginning to develop near that
boundary, as well as in the central Black Hills along convergence
boundary.

Atmosphere is having somewhat of a hard time recovering from last
night`s MCS, but there is still a few more hours of heating to
go. Airmass to the south of the aforementioned secondary low/front
is destabilizing with MLCAPE currently around 500 J/KG to near
1000 J/KG towards the NEB border, and those values should continue
to creep upwards this afternoon. Convection is expected to
increase this afternoon into the evening, mostly from northeast WY
and southwest SD into the Black Hills and west central SD, as
short wave embedded in southwest flow aloft approaches. While
shear is quite modest, a few stronger to possibly severe storms
are expected mainly over far southwest SD and the Black Hills, and
possibly southern portions of Campbell and Weston counties.
Airmass further to the north, generally near and north of I-90,
does not look to support much severe threat. Activity will
gradually weaken later this evening and overnight.

Upper low will form over eastern CO and track into central NEB on
Saturday, with chilly temps and some gusty northerly winds for our
area. Best chance for -shra will be south of I-90 across western
SD.

Upper level ridge building into our region should bring warmer and
mainly dry conditions for the end of the weekend into early next
week. Southwest flow aloft returns for mid/late week bringing more
unsettled weather.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Saturday Evening)
Issued At 518 PM MDT Fri May 18 2018

Scattered showers and thunderstorms are expected ahead of a cold
front through the early overnight hours, particularly across
southwestern SD and near the Black Hills. MVFR cigs and brief
reductions in vsbys are possible in any showers/storms.

Behind the cold front tonight, gradually deteriorating cigs are
expected, becoming MVFR to IFR area-wide. Some limitations to
vsbys due to BR/FG are also expected. In addition, gusty north to
northeast winds will develop late tonight through tomorrow.

&&

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

$$

DISCUSSION...Johnson
AVIATION...JC



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