Area Forecast Discussion
Issued by NWS Rapid City, SD

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812
FXUS63 KUNR 191757
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1157 AM MDT Wed Jul 19 2017

.DISCUSSION...(Today Through Tuesday)
Issued at 255 AM MDT Wed Jul 19 2017

Current surface map places high pressure across Minnesota.
Stationary front located across northern Nebraska into Wyoming
with area of low pressure along the front in southern Montana.
Isolated thunderstorms continue to weaken across southwest South
Dakota, while thunderstorm activity increasing across northwest
South Dakota into eastern Montana and North Dakota.

Shortwave across Montana rides through North Dakota today.
Warm front lifts into western South Dakota as Montana surface low
tracks to the Black Hills this afternoon. Short range models in
decent agreement with thunderstorms increasing in coverage this
morning north of the forecast area with a few clipping northwest
South Dakota. As surface sets up near Black Hills this afternoon,
thunderstorms expected to develop around the Hills and expand
eastward along the warm front. Moisture pooling along the warm
front will provide plenty of instability, with MLCAPE of 3000+
J/KG from the Black Hills into central South Dakota. Sufficient
shear for a few supercells, especially east of the Black Hills.
Thunderstorms will linger into tonight mainly south of I-90. Will
continue with Heat Advisory across south central South Dakota this
afternoon and evening with Heat Index around 105F.

Another active day on Thursday as upper level shortwave crosses
western South Dakota. Sufficient instability and shear for more
severe thunderstorms. Area will remain under flat upper ridge
through Friday. Strong wave topping the ridge Saturday/Sunday
will allow for some cooling as cold front moves through. Ridge
builds back early next week with above average temperatures and
small chances for thunderstorms.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1157 AM MDT Wed Jul 19 2017

Isolated thunderstorms will redevelop this afternoon and evening
across the Black Hills and portions of the northeast Wyoming and
western South Dakota plains. A cold front will continue to cross
the western SD plains this afternoon with winds gusting up to 50
mph behind the front in the vicinity of KRAP. VFR conditions
expected outside of any thunderstorm development.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 7 PM MDT /8 PM CDT/ this evening for SDZ032-
     043-044-046-047-049.

WY...None.
&&

$$

DISCUSSION...7
AVIATION...13



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