Area Forecast Discussion
Issued by NWS Rapid City, SD

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110
FXUS63 KUNR 152138
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
338 PM MDT Tue Aug 15 2017

.DISCUSSION...(This Evening Through Tuesday)
Issued at 338 PM MDT Tue Aug 15 2017

Current surface analysis shows low pressure over northwest NE,
with warm front extending east across northern NE and cool front
south and west of the area. Upper level analysis shows low
pressure across southwest SK, with upper trough now extending
south across the Northern Rockies into the central Rockies. KUDX
radar shows scattered showers now across mostly northwest SD, with
isolated showers and thunderstorms developing elsewhere. Regional
radars show more activity moving northeast across southeast WY
and parts of western NE. Temps range from the 60s over northeast
WY and the Black Hills to the low to mid 80s across south central
SD. Winds are north to northwest across northeast WY and far
western SD, south to southeast over central SD.

The main shortwave to the southwest of the region will move
northeast into the Central Plains by early this evening. The
northern edge of shower and thunderstorm activity associated with it
will affect southwest and south central SD this evening. Locally
heavy rain is possible with plenty of moisture in place and
precipitable water values above average. The threat for severe
storms across our area still looks greatest near the surface low as
it tracks across northern NE. MLCAPE values southeast of the Black
Hills are progged to be in the 1000 to 1500 j/kg range later this
afternoon with favorable shear, especially toward south central SD.
Hail and strong wind gusts will be the main threats from any severe
storms. Timing for the severe storm threat now looks to be late
afternoon and early evening. Further north, activity should be more
isolated and weaker, with dry conditions across the far northern and
western CWA. Activity will end from northwest to southeast
overnight, with some activity possibly lingering across south
central SD into early Wednesday.

Northwest flow aloft will persist Wednesday and Thursday, with
cooler conditions persisting Wednesday behind exiting system. 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. Some chances for showers and storms could
return early next week as flow is progged to turn more
northwesterly. Temperatures look to be near to slightly below
average.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1127 AM MDT Tue Aug 15 2017

Scattered to numerous SHRA/TSRA will continue through this evening
with mainly MVFR CIGS/VSBYS. Local IFR conditions may occur with
the strongest storms. After 04z, expect mostly VFR conditions with
leftover local MVFR CIGS possible given moist boundary layer.

&&

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

$$

DISCUSSION...26
AVIATION...10



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