Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 132029
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
229 PM MDT Mon Aug 13 2018

.DISCUSSION...(This Evening Through Monday)
Issued at 144 PM MDT Mon Aug 13 2018

Current upper level analysis shows a ridge axis that is centered
over the Upper Midwest today as a slow moving upper low spins over
Kansas, eastern Colorado, and Oklahoma. A Pacific NW trough is
pushing into southern Alberta and northern Montana this afternoon
and will continue to push south and eastward in the coming days.
Surface low pressure centered in central South Dakota with cold
front extending from central North Dakota into southeastern
Wyoming. Winds have turned northwesterly to northeasterly behind
the front with accompanying wind gusts up to 20-25 mph.

As the cold front exits the region, some showers and
thunderstorms are possible across northeastern Wyoming and
northwestern South Dakota this evening and may linger into early
Tuesday morning. The passage of the cold front will usher in cooler
air Tuesday with highs in the upper 70s to near 80.

The aforementioned shortwave dropping out of the Pacific NW will
move into the region Tuesday into Wednesday. Chances for rain and
thunderstorms will increase Tuesday afternoon ahead of this wave.
There is a chance for severe weather Tuesday afternoon into the
evening with MUCAPE around 1000 J/kg and bulk shear of 30-45 knots.
While conditions look marginal, the severe threat will
be limited to northeastern Wyoming, although a strong to severe
storm cannot be ruled out over the Black Hills and southwestern
South Dakota. Storm coverage will be isolated with hail and wind
the primary threats accompanying any strong storms.

Upslope, southeasterly flow will prevail Wednesday as upper level
trough slowly exits the region. Resulting environment will be
characterized by MUCAPE upwards of 1500 J/kg across western South
Dakota and northeastern Wyoming along with bulk shear around 30-50
knots. While storm coverage is expected to be isolated, severe
weather is possible Wednesday afternoon and evening with any
stronger storms capable of severe wind or hail.

Following passage of the upper level trough on Wednesday, another
weak upper level ridge will build over the region with
temperatures increasing into the mid 80s to near 90 for the
latter half of the week. Guidance continues to remain in good
agreement on another upper level trough pushing into the western
U.S. this weekend. Attendant shortwaves will round the base of
the trough and bring multiple rounds of showers and storms through
the weekend.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1113 AM MDT Mon Aug 13 2018

VFR conditions are expected through the TAF period, although some
areas of smoke may lower the visibility to less than 10 miles at
times. Gusty north/northeast winds will continue through this
evening. Isolated thunderstorms may occur late this
afternoon/early this evening with better chances Tuesday.

&&

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

$$

DISCUSSION...Eagan
AVIATION...Helgeson



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