Area Forecast Discussion
Issued by NWS Rapid City, SD

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867
FXUS63 KUNR 172050
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
250 PM MDT Thu Aug 17 2017

.DISCUSSION...(This Evening Through Thursday)
Issued at 250 PM MDT Thu Aug 17 2017

Current surface analysis shows surface trough east of the Black
Hills, with west-northwest winds behind it and south- southwest
winds toward central SD. Upper level analysis shows weak shortwave
from western ND to eastern WY. KUDX radar shows isolated to
widely scattered showers and storms along and behind the surface
trough from northeast WY to far western SD. Temps range from the
low to mid 80s over northeast WY and far western SD to the low to
mid 90s across parts of south central SD.

Isolated to scattered showers and thunderstorms will spread east
across the rest of the area through the late afternoon and evening
hours, ending from west to east in most areas by midnight.
Instability is relatively weak across the area, 500 j/kg or less, so
any stronger storms should mostly produce small hail and gusty
winds. Lows tonight will mostly be in the 50s.

A warm and dry airmass will spread over the area for Friday and
Saturday. The warmest day will be Saturday as highs reach into the
90s across much of the SD plains. Another surface trough/weak cool
front will cross the area in the afternoon and evening. There could
be isolated showers and storms across the Black Hills area in the
afternoon. Will start to see a more widespread chance for showers
and storms late in the weekend into early next week as flow aloft
becomes more active from the northwest and upslope flow at the
surface brings increasing moisture into the area. There is a slight
risk for severe storms over much of western and south central SD
late Sunday into Sunday evening. Some mid and high cloud cover could
persist across the area Monday morning/midday before chances for
storms increase across parts of the area in the afternoon.
Temperatures will generally be near average through at least the
middle of next week. An upper level ridge is still progged to build
over the Rockies and into the high plains mid to late week, with
thunderstorm coverage expected to mostly be isolated.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Friday)
Issued At 1132 AM MDT Thu Aug 17 2017

A few thunderstorms will move across the area this afternoon into
tonight. Local MVFR conditions with the thunderstorms, otherwise
VFR conditions expected.

&&

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

$$

DISCUSSION...26
AVIATION...JC



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