Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 050420

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1020 PM MDT Tue Aug 4 2020

.DISCUSSION...(This Evening Through Tuesday)
Issued at 119 PM MDT Tue Aug 4 2020

Upper level analysis shows compact shortwave pushing eastward across
southern Saskatchewan with trough axis extending southward into the
northern plains. Surface trough axis extends from developing low
pressure across NE Colorado this afternoon. Modest MUCAPE
(1000-2500 J/kg) will be in place this afternoon and evening,
although shear will be marginal. Broad upper level ascent via
shortwave trough coupled with convergent flow along the southern
Black Hills will provide impetus for thunderstorm development. The
overall environment will be conducive to a few strong to severe
storms through the evening before tapering off later tonight.
Widespread severe weather is not anticipated this evening.

Northwest flow continues Wednesday with chances for a storm or two
through the day Wednesday, mainly across SW SD, although the best
chances will remain to our northeast and south of the forecast area.
Mid-level warm air advection spreads into the northern Plains
overnight Wednesday as upper level ridge builds Thursday into
Friday. Temperatures will warm back into the upper 80s to 90s for
most locations to end the week.

Southwesterly flow aloft becomes the dominant pattern moving into
the weekend with embedded waves rippling through the flow. While the
best upper level forcing will remain well off to the north,
orographic forcing coupled with subtle waves will likely be enough
to support at least a small chance of thunderstorms each day Thursday
through the weekend. A thermal ridge will be in place across the
region Thursday into Friday, with warm air aloft and subsequent
capping concerns likely limiting more widespread storms.
Additionally, bulk shear looks rather weak through Saturday (20 to 35
knots), further limiting overall severe potential. At this point,
greatest likelihood for showers and storms looks to remain across
south-central into eastern SD each day where higher quality boundary
layer moisture will be in place.

Westerly to southwesterly flow will continue through the weekend
into next week with temperatures near normal and generally dry
conditions expected. Dry westerly flow will likely result in
elevated fire weather concerns beginning this weekend. At this point
winds look to remain below criteria, however minimum daily RH values
will likely fall into the teens, particularly across SW SD and NE WY
this weekend into early next week.


.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1018 PM MDT Tue Aug 4 2020

Areas of MVFR/IFR cigs and vsbys possible over central SD
overnight. Otherwise, mainly VFR conditions expected through
Wednesday. Isolated thunderstorms are possible over parts of
northeast WY and southwest SD Wednesday afternoon/evening.




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