Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 221116

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
516 AM MDT Fri Jun 22 2018

.DISCUSSION...(Today Through Thursday)
Issued at 157 AM MDT Fri Jun 22 2018

An upper wave over the northern Rockies is helping to
produce some thunderstorms across southeastern MT/southwestern
ND/northwestern SD/northeastern WY. Surface high rests over central
NE, and with the surface trough approaching from the west, winds are
southerly around 10 kts. Temperatures at 2 AM are in the 50s and
lower 60s.

Showers and thunderstorms will continue across northwestern SD this
morning. Activity will expand across much of the CWA this afternoon,
as the upper wave an its associated cold front slide into the
northern plains. MLCAPE of 1000-2000 J/kg could allow for a couple
strong to severe storms; however, 0-6 km shear is weak. Greater
chances for severe storms will be to the south, where instability
and shear are better. Highs today will be in the 70s to lower 80s,
cooler across the northwestern half of the CWA.

Precipitation will linger across northwestern SD to south central SD
and eastward Saturday, before the first wave finally exits the
region. Weak ridging will allow for a brief period of dry weather
for the western CWA before the next system moves in. Positively
tilted upper wave will dig into the central Rockies late Saturday,
and slowly cross the northern plains this weekend into early next
week. Both the GFS and NAM show the upper low sliding just to the
south of the CWA, while the ECMWF has it farther north.
Showers/storms are expected to begin pushing into the area
Saturday evening, with widespread precipitation on Sunday, and
rain lingering into Monday. Models are showing 1-2 inches of QPF
possible, mainly across the southern parts of the CWA. With PWATs
150% of normal and slow storm motion over a couple of days of
precipitation on already saturated soils, a flood watch may need
to be considered for Sunday/Monday. Will hold off for now, in case
the track of the low shifts. Temperatures through the weekend
will be mainly in the 70s.

Slight ridging/zonal flow is expected for the middle of next week,
resulting in warmer and drier weather.


.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 515 AM MDT Fri Jun 22 2018

Scattered thunderstorms will move across northwest South Dakota
this morning, and across much of the area this afternoon and
evening. IFR conditions with the stronger thunderstorms.




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