Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 111005
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
405 AM MDT Fri Aug 11 2017

.DISCUSSION...(Today Through Thursday)
Issued at 326 AM MDT Fri Aug 11 2017

Upper level analysis has broad trof across the northeastern and
north central CONUS, with slight ridging across the West Coast.
Shortwave is currently sliding south across Alberta in the broad
cyclonic flow. Skies across the Northern Plains are mostly clear.
At the surface, high pressure resides across the Northern Plains.
Temperatures at 3am are in the 50s with light south to southeast
winds.

Weak cyclonic upper flow will continue across the area today with
Alberta upper shortwave sliding into Montana by afternoon. At the
surface, high pressure will shift to the east with breezy
southerly return flow winds expected. High temperatures will be in
the upper 70s to mid 80s across the area.

Ahead of the upper shortwave, weak upper disturbances will cross
the forecast area this afternoon, and combined with moderate
instability and shear, should produce scattered thunderstorms
across the area. With MUCAPE values over 1000 J/kg and shear
values ranging from 25-40 m/s, a few storms have the potential to
become severe across parts of Northeast Wyoming and far western
SD, with hail and strong winds the greatest concern.

Showers and thunderstorms will continue across western South
Dakota into the evening hours, with a few strong storms still
possible. Activity will slowly shift east during the night, with
some areas of fog possible across the southwest South Dakota
plains after midnight.

The weekend continues to look unsettled and relatively cool as the
Alberta shortwave slowly slides southeast across the Northern
Plains. Saturday looks to be the more active day with widespread
scattered storms expected as the surface boundary remains over
southern and western portions of the CWA. East-southeast low level
flow will continue to bring increasing moisture into most of the
area, especially over western SD, where CAPE values up to 2000
J/kg are expected. This looks to be the most favorable day for
severe weather potential in most areas, with the Storm Prediction
Center having much of the area in a marginal to slight risk of
severe weather. Additionally, PWs will be higher than we have seen
in recent weeks, so storms should produce some beneficial
rainfall.

Storm potential on Sunday looks to be mostly confined to the
Black Hills area and south central SD at this point as Alberta
shortwave begins to slide southeast of the region. We will begin
to see a warmer and somewhat drier weather pattern early next week
as West Coast ridge builds over the region. Temperatures should
be back to average levels by midweek. We will continue to see at
least isolated thunderstorm activity at times through midweek,
with perhaps more widespread activity Tuesday afternoon and
evening.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued at 1014 PM MDT Thu Aug 10 2017

VFR conditions are expected through the period. Thunderstorms will
develop across portions of the region Friday. Local MVFR-IFR conds
possible in/near thunderstorms.

&&

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

$$

DISCUSSION...15
AVIATION...JC



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