Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 192332
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
532 PM MDT Sat Aug 19 2017

.DISCUSSION...(This Evening Through Saturday)
Issued at 216 PM MDT Sat Aug 19 2017

Weak upper ridging is crossing the Dakotas with a low amplitude
shortwave trough pushing into the northern Rockies into central
Montana. Surface trough is drifting across the CWA at this time with
light winds across the western SD plains just east of the Black
Hills. Cold front boundary is farther northwest...just beginning to
push into northwest SD and almost to northeast WY. Cumulus clouds
have developed across the Black Hills with no storm development.
Some isolated storms may still develop over the next two or three
hours...but any that do develop will stay over the Black Hills and
dissipate by early evening. The cold front will push through the CWA
this evening with temperatures cooling into the upper 60s and
70s...and smoke clearing across the area. Overnight lows will be
in the 50s to low 60s. Montana shortwave will cross parts of NE WY
into NW SD with showers and thunderstorms developing late tonight
into early Sunday morning.

Surface high will move into the Dakotas Sunday with cooler temps
in the mid 70s to mid 80s and mostly sunny skies. High pressure
moves off to the east with return flow setting up along with
strong theta E advection Sunday night. Another weak wave will
cross around NW SD late Sunday evening into the overnight hours
with storms developing. Looks like an MCS will push through NW SD
into the west central SD plains and perhaps edging the Black Hills
area. This will push southeast into south central SD Monday
morning. If this scenario pans out...it could leave low clouds
around parts of western SD and more likely into south central SD
around the time of the eclipse. Highs Monday will reach the mid
70s to mid 80s again. Strong high pressure will dominate the
region Dakotas into the middle of next week with drier air and
seasonable temps. Upper ridge axis is progged to cross the region
Wed/Thu with southwest flow developing. This could bring a warmer
and more active pattern to the area for the second half of the
week.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening)
Issued At 529 PM MDT Sat Aug 19 2017

Some patchy MVFR FU tonight. Isolated/scattered -TSRA possible
later tonight/early Sunday across northwest SD with local MVFR
conditions. Additional -TSRA possible late Sunday. Otherwise, VFR
conditions expected.

&&

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

$$

DISCUSSION...13
AVIATION...Helgeson


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