Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 161818
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1218 PM MDT Wed Aug 16 2017

.UPDATE...
Issued at 1035 AM MDT Wed Aug 16 2017

Current surface analysis shows low pressure over far northeast NE,
with surface trough stretching west-northwest from the low into
central SD. Upper level analysis shows main upper trough now
located across central SD to eastern CO, slowly moving to the
east-northeast. Skies range from clear across northeast WY to
cloudy over south central SD. KUDX radar continues to show showers
from eastern Jackson and Bennett counties through Tripp County.
This activity is not moving much at this time and has expanded in
coverage over the last hour. Temps are mainly in the mid 60s to
lower 70s right now with northerly winds mostly in the 5 to 15 mph
range, a bit stronger across parts of the western SD plains.

Have updated the forecast to mainly extend shower coverage across
south central SD through the early afternoon. Latest models have
activity eventually shifting east of the CWA around 21z. There
could be a few rumbles of thunder this afternoon before activity
ends, but will keep just a shower mention for now. Have also made
some adjustments to cloud cover over the eastern CWA, with south
central SD staying mainly cloudy through late afternoon. Temps may
need to be adjusted a bit as well later today, especially over
the eastern CWA.

&&

.DISCUSSION...(Today Through Tuesday)
Issued at 349 AM MDT Wed Aug 16 2017

Upper level analysis has a trof across the western CONUS, and
another across New England with weak ridging across the Great
Lakes region. Skies are mostly cloudy across the Northern Plains
with a large thunderstorm complex producing rain from central
Nebraska into south central South Dakota. At the surface, weak low
pressure and weak trof reside across the central and eastern
Dakotas, with main low across Kansas. High pressure is settling
into the Northern Rockies behind the surface trof. Temperatures
across the area at 3am are in the 50s and 60s with light northerly
winds. Some patchy fog is present across parts of northwest South
Dakota.

Upper level trof across the western CONUS will shift into the
Northern Plains as the surface trof move east of the area. Patchy
fog across parts of northwest SD will dissipate early this morning
as drier air moves in. Light shower activity will persist across
south central SD this morning, pushing east by late morning as
northwest flow aloft and surface high pressure takes over. With
clearing skies, temperatures will respond nicely, rising into the
70s to lower 80s across the area. Clear and cool conditions are
expected tonight with low temperatures in the 50s.

Northwest flow aloft will persist into Thursday, with temperatures
finally rising closer to seasonal normals. A shortwave
disturbance will bring isolated to scattered showers and storms
Thursday afternoon and evening to most areas. The threat for
severe storms looks low at this time, with the best potential at
this time looking to be across southwest SD late in the day.

Near zonal flow and weak ridging is expected for the end of the week
and this weekend, with mainly dry weather and near to slightly above
average temperatures. An isolated thunderstorm or two will be
possible over the Black Hills area this weekend. Some chances for
showers and storms could return early next week as flow is
progged to turn more northwesterly. Temperatures look to be near
average early next week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1218 PM MDT Wed Aug 16 2017

VFR conditions are expected through the forecast period. Breezy
northwest winds across the western SD plains will decrease early
this evening.

&&

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

$$

Update...26
DISCUSSION...15
AVIATION...13



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