Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 191051

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
451 AM MDT Sun Aug 19 2018

.DISCUSSION...(Today Through Saturday)
Issued at 254 AM MDT Sun Aug 19 2018

Current upper level analysis places a strong trough centered over
the western Dakotas and eastern Wyoming and Colorado, extending
southward into the southern Plains. Current surface analysis has low
pressure centered in north-central South Dakota with surface
trough extending southward into Nebraska with a cold front near the
North Dakota-South Dakota border. Widely scattered showers and a few
thunderstorms are ongoing across the area.

Cool, cloudy, wet, and blustery weather will continue today as the
upper level trough pivots out of the region. Showers and a few
thunderstorms will end by late morning in the northwest portion of
the forecast area and by late evening for our southeastern counties.
In addition to the rainfall today, winds will be rather gusty
with gusts up to 40 mph possible over parts of the South Dakota
plains. Additionally, much cooler air will filter in today behind
the cold front with temperatures struggling to get out of the 60s
for most areas except for the Black Hills where highs will be even
cooler - only in the mid 50s.

Another quick moving wave will clip the area late Monday into the
overnight hours with showers and a few rumbles of thunder possible.
Following this system, flow turns more zonal with a weak ridge
building back into the region for the latter half of the week.
Temperatures will warm to slightly above normal with generally drier

The upper level ridge will flatten out by midweek with another wave
forecast to move through the region Thursday. While guidance differs
slightly on timing, the European a bit slower than the GFS,
showers and thunderstorms look likely Thursday. The CAPE/shear
parameter space does hint at a possible severe threat Thursday
afternoon and evening, particularly east of the Black Hills into
central South Dakota.

For the end of the week into the weekend, ensemble guidance shows
zonal flow dominating the northwest US, albeit with some
differences. Regardless, conditions will likely be warmer and drier
moving into the weekend.


.AVIATION...(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 447 AM MDT Sun Aug 19 2018

Showers and isolated thunderstorms will continue through this
afternoon, then end from east to west...with showers lingering
across south central South Dakota tonight. MVFR/local IFR
ceilings will persist across northeast Wyoming and western South
Dakota through this afternoon, with the lowest ceilings around the
Black Hills. Northwest winds gusting to 30-40 kt will continue
through mid-afternoon on the South Dakota plains.




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