Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 151743
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1143 AM MDT Fri Sep 15 2017

.DISCUSSION...(Today Through Thursday)
Issued at 215 AM MDT Fri Sep 15 2017

Latest analysis shows upper trough over western CONUS with a
number of disturbances rotating northward on the eastern side of
the trough and across the forecast area. The upper trough will
slowly cross the region, finally moving off to the east of the
forecast area on Saturday night. A relatively strong shortwave
will lift northward across the forecast area today. The strength
of the lift associated with the shortwave combined with steep mid
level lapse rates and high precipitable water values will result
in widespread showers, and a few thunderstorms. The highest
rainfall amounts are expected to be located over northeastern
Wyoming and northwestern South Dakota. High temperatures will
vary greatly across the region today, ranging from the lower 50s
over parts of northeastern Wyoming and northwestern South Dakota
to the lower to mid 70s over south central South Dakota. As the
shortwave crosses the region this afternoon the best forcing will
shift northward, leading to high pops north and lower pops across
the south this afternoon. There remains a chance of showers across
much of the area tonight as the upper trough continues to affect
the region. Low temperatures on Saturday morning may be cold
enough for some light snow in the higher elevations of the Black
Hills with a mix possible for portions of northeastern Wyoming. As
the upper trough crosses the area Saturday, steep lapse rates
will result in diurnal trend to showers.

The models remain in decent agreement next week with another deep
trof moving into the western CONUS. The models continue to show
some timing differences, especially during the second half of next
week. Shortwave ridging ahead of the trof will bring warm and dry
days Monday and Tuesday, followed by cooler and unsettled weather
for the second half of the week with increasing chances of
precipitation.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Saturday)
Issued At 1141 AM MDT Fri Sep 15 2017

Showers and isolated thunderstorms will continue to produce
MVFR/IFR/local LIFR conditions through the forecast period. Lowest
CIGS will be across the Black Hills and portions of northeast
Wyoming.

&&

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

$$

DISCUSSION...10
AVIATION...13



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