Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 142325
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
525 PM MDT Thu Sep 14 2017

.DISCUSSION...(This Evening Through Thursday)
Issued at 159 PM MDT Thu Sep 14 2017

Current surface map shows cold front through south central South
Dakota into southwest Nebraska. Smoke/hazy skies along with a few
clouds across the area this afternoon. Water vapor places deep
trof along the west coast. Weak shortwave moving through Wyoming
with strong shortwave lifting into southern Utah. Initial
shortwave will bring a few showers overnight, mainly across the
western half of forecast area. Strong shortwave lifts through
eastern Wyoming/western South Dakota Friday. Strength of
shortwave combined with steep mid level lapse rates and high
precipitable water will result in widespread precipitation Friday.
Highest rainfall amounts focused across northeast Wyoming into
northwest South Dakota. Clouds/precipitation will keep highs
Friday in the 50s for northeast Wyoming/northwest South Dakota.
Best forcing shifts north of the forecast area late Friday, though
a few showers will linger into Friday night. Temperatures
marginally cold enough for some light snow in the higher
elevations of the Black Hills with a mix possible for portions of
northeast Wyoming. Upper trof moves across the area Saturday.
Steep lapse rates will result in diurnal trend to showers.

Models in decent agreement next week with another deep trof
moving into the western CONUS. Some timing differences, especially
last half of next week. Shortwave ridging ahead of the trof will
bring warm and dry days Monday-Tuesday. Cooler and unsettled for
last half of the week with increasing chances of precipitation.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 522 PM MDT Thu Sep 14 2017

Areas of MVFR FU will diminish tonight as a storm system
approaches the region. SHRA/TSRA with local MVFR conditions will
continue to develop over northeast WY and then spread east into
western SD tonight. MVFR/IFR CIGS will develop over northeast
WY/western SD overnight with local LIFR conditions over the higher
terrain of the Black Hills due to upslope ST/FG.

&&

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

$$

DISCUSSION...7
AVIATION...Helgeson



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