Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 170930

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
330 AM MDT Wed May 17 2017

.DISCUSSION...(Today Through Tuesday)
Issued at 330 AM MDT Wed May 17 2017

Current surface analysis shows low pressure centered over western
KS, with frontal boundary extending northeast of the low into
southern MN. A cold front stretches across southern ND, slowly
moving south into the area. Upper level analysis shows low
pressure over southwest KS, moving northeastward. Another low is
located over northeast OR, sliding southeastward. Regional radars
showing an area of showers and a few storms over north central NE
and south central SD. More isolated shower activity has developed
further north into portions of west central and northwest SD.
Skies are mainly cloudy in most areas with some partly cloudy
skies over toward the Gillette area. Some fog is developing over
the higher Black Hills, with patchy fog potentially developing
down onto the surrounding plains toward morning as upslope east-
northeast winds are slowly increasing. Temps range from the lower
40s at Gillette to near 60 over south central SD.

A complex weather setup is in place for the next couple of days, as
the system over the Central Plains brings some rainfall to mostly
southern and eastern portions of the CWA today and the next system
to the west begins to impact western portions of the area later
today and tonight. Medium range models continue to have some
difficulty with this, but are at least in decent agreement with the
Central Plains system today. The best chances for rainfall and more
significant amounts with this system will be southeast of the Black
Hills into south central SD today. There still will be a good
chance for rainfall across southwest SD and the Black Hills, but
amounts will be less than was expected as the low has remained
further south of the area. A few thunderstorms are also possible
across SD, but forecast instability is quite a bit less than
previous days, so the threat for any stronger storms is minimal at
best. Cold front will slowly move south across the area during
the day. Temps should be a bit warmer than was expected with
slower front and less pcpn in most areas. Highs in the mid 50s to
lower 60s across the plains and low to mid 50s in the Black Hills.
Pcpn with plains system should move quickly out of eastern areas
late this afternoon/early evening as low races to the northeast
and out of the region.

Further west across WY, conditions look mostly dry early today, with
increasing chances for showers and thunderstorms toward the
afternoon as shortwave energy rotates into the area ahead of the
western system. There is a better chance for thunderstorms over
northeast WY this afternoon, with MUCAPE values of 500 to 1000 j/kg
progged across the area. Would not be surprised to see a strong
storm or two with gusty winds and small hail later this afternoon.
The best chances for pcpn will continue across northeast WY and
possibly into southwest SD tonight as upper low moves into the
Central Rockies. Temps look to be a bit warmer overnight, so any
snow should mainly be limited to the higher Black Hills, but pcpn
amounts there will be on the light side. Lows will be in the mid 30s
to mid 40s.

Good chances for rain will persist across northeast WY and southwest
SD Thursday, then slowly spread north and east across much of the
CWA Thursday night into Friday. Colder air Thursday night will
likely bring a better chance for some snowfall across the BH and the
higher elevations of northeast WY into Friday morning. Some
accumulation is possible. Could even see some snow across far
southwest SD into the Pine Ridge if temps become cold enough. Upper
low will pivot northeast into the Central and Northern Plains on
Friday into Friday night, bringing more widespread chances for pcpn.
Highs only in the 40s and lower 50s. Pcpn will diminish and exit the
area Friday night and early Saturday as upper low weakens and moves
northeast of the region. Lows Friday night will be close to freezing
in spots on the plains and if skies clear enough toward morning
there could be some frost.

Much of the weekend looks dry, but on the cool side. More seasonable
temperatures will return for Sunday and into early next week.
Northwest flow will be dominant during this time, with breezy
conditions likely at times and occasional disturbances bringing
chances for showers and storms from late Sunday through the first
half of next week.


.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1105 PM MDT Tue May 16 2017

A few showers/isolated thunderstorms will linger overnight, mainly
over southwest and south central South Dakota. Widespread
MVFR/IFR ceilings will develop overnight with some LIFR
conditions around the Black Hills. IFR ceilings will remain across
portions of northeast Wyoming, the Black Hills, and southwestern
South Dakota through Wednesday morning, with some improvement late
morning/early afternoon. Coverage of showers will increase
Wednesday across northeast Wyoming into southwest South Dakota.




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