Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 190930

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
330 AM MDT Sat Aug 19 2017

.DISCUSSION...(Today Through Friday)
Issued at 137 AM MDT Sat Aug 19 2017

Upper ridge axis is moving over the northern plains, while a
trough pushes into the Pacific Northwest. Water vapor shows dry
air over the CWA, also depicted by the clear satellite. Surface
trough sits over eastern WY/MT. Winds are southeasterly around 10
kts, and temperatures are around 60.

Thermal ridge axis over the CWA today will result in very warm
temperatures in the 90s. Upper trough will flatten the ridge, and
the surface trough/cold front will push through the area. A mainly
dry day is expected, except for an afternoon shower/storm over the
Black Hills, and the potential for Nebraska`s storms to clip south
central SD in the evening. Then after midnight, a few showers/storms
will be possible across northwestern SD.

Sunday will be slightly cooler, with highs in the 80s. Surface high
will slide across ND, and southeasterly winds will increase across
the CWA. Models have lowered their MLCAPE forecasts for Sunday
afternoon/evening, but best instability still looks to be across
south central SD. A weak disturbance moving through zonal flow may
spark a few storms, and a few strong to severe storms will be
possible in the evening and overnight.

A stronger wave will push through the northern plains Monday,
bringing additional chances for showers and thunderstorms. Both the
ECMWF and GFS are showing precipitation beginning in the morning,
while the Canadian holds off until the afternoon. Models have come
in cloudier than previously. Following this wave, an upper ridge
will bring drier weather for much of next week, along with near
average temperatures.


.AVIATION...(For the 12Z TAFS Through 12Z Sunday Morning)
Issued At 329 AM MDT Sat Aug 19 2017

Isolated thunderstorms are possible over the Black Hills this
afternoon and into portions of northeast Wyoming and northwest
South Dakota tonight. Local MVFR conditions with the
thunderstorms, otherwise VFR conditions through tonight.


Issued At 137 AM MDT Sat Aug 19 2017

Today will be hot and dry. As temperatures warm into the 90s,
minimum RH will drop to around 15 to 20% across much of the CWA.
However, winds will be light for most places. A cold front will
bring some breezy winds to far northwestern SD, but they are
expected to remain below criteria.




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