Area Forecast Discussion
Issued by NWS Rapid City, SD

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155
FXUS63 KUNR 142122
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
322 PM MDT Tue Aug 14 2018

.DISCUSSION...(This Evening Through Tuesday)
Issued at 322 PM MDT Tue Aug 14 2018

Current surface analysis shows cold front south and east of the
forecast area. Upper level analysis shows an area of low pressure
over eastern portions of the Central Plains, with a shortwave
trough over the eastern half of MT. High pressure remains across
the Four Corners region. Skies are variably cloudy with an area of
showers and thunderstorms over parts of southwest into south
central SD, gradually dissipating. Regional radars show storms
developing west of the forecast area, especially over the higher
terrain. Temps are in the mid 60s to upper 70s, with winds
southeasterly or becoming southeasterly across much of the area.

Unsettled weather will continue over the next couple of days as the
upper level system slowly moves across the Northern Plains. Storms
to the west will move into northeast WY late this afternoon/early
evening and into western SD this evening/overnight. The best
instability late this afternoon and evening will be across eastern
WY to far southwest SD, 1000 to 1500 j/kg MUCAPE. Shear will be
quite favorable for stronger storms/supercells across northeast WY.
There is a slight risk for severe storms across northeast WY with
large hail and strong wind gusts the main threats. Shear profile in
the lower levels would suggest that a tornadic storm cannot be ruled
out over northeast WY as well late today. With precipitable water
values 125 to 150 percent of average, there will be locally heavy
rainfall with stronger storms today and tonight.

The trough will close off over the Northern Plains Wednesday and
Wednesday night, with scattered to numerous showers and
thunderstorms expected in many areas. The exceptions will likely be
across western parts of northeast WY and far northwest SD. Forecast
instability will be sufficient for stronger storms from the Black
Hills eastward in the afternoon/early evening. Highs will
generally be in the 70s to around 80. Activity will slowly end
from west to east late Wednesday and Wednesday night. Will keep
some low chances across south central SD into Thursday. Otherwise,
warmer and mainly dry weather is expected Thursday into Friday as
a shortwave ridge moves across the region.

Another fairly strong upper level system for this time of year will
move across the area over the weekend, bringing good chances for
showers and storms Saturday and Sunday. There is potential for some
severe storms and heavier rainfall across at least portions of the
area. That system will exit early in the week, with some drier
weather returning for the first half of the week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1110 AM MDT Tue Aug 14 2018

A broken line of thunderstorms will move across western SD with
local MVFR conditions through the afternoon hours. Additional
strong thunderstorms will develop across northeast WY later this
afternoon, moving through  SD this evening with local IFR
conditions. Outside of storms, VFR conditions are expected through
the period.

&&

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

$$

DISCUSSION...26
AVIATION...Helgeson



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