Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 131717
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1117 AM MDT Sun Aug 13 2017

.DISCUSSION...(Today Through Saturday)
Issued at 300 AM MDT Sun Aug 13 2017

Upper level analysis has strong shortwave rotating through
central ND in larger broad trof across the Great Lakes area and
the northeast CONUS. Skies across the Northern Plains are partly
to mostly cloudy. Some isolated showers and light thunderstorms
still across eastern parts of the CWA. At the surface, weak low
pressure is located near the Philip area, with high pressure
across ND. Patchy fog has developed across parts of south central
SD, with better areas of fog across far northwest SD.
Temperatures at 3am are in the 50s and lower 60s, with winds light
out of the north at most locations.

Today...Upper level shortwave will continue to slide east of the
area this morning, along with the thunderstorm activity. A
mainly dry day is expected today as a weak upper ridge briefly
builds over the region. A few thunderstorms may develop over the
Black Hills early this afternoon during peak heating. A weak mid
level shortwave will pass through the ridge late this afternoon
and evening, producing additional storms mainly across the
southwestern 1/3 of the CWA. Decent shear and some marginal
instability may result in a few stronger storms. Highs will be in
the mid 70s to mid 80s.

Ridge axis will cross the northern plains Monday, and temps will
warm slightly. A series of waves associated with a Canadian low
pressure system will begin approaching the area in southwest flow,
the first of which is expected to spark another round of showers and
thunderstorms late Monday afternoon and evening. Decent
instability and shear will support a few strong to severe storms
again.

Medium range models are digging a fairly strong trof across the
Northern Rockies by Tuesday, which could produce some fairly
widespread chances for showers/storms for much of the day and into
Wednesday. Both the GFS and ECMWF agree on a broad ridge building
over the western CONUS towards the end of the week, bringing
drier weather. Temperatures are expected to be near average
through the week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Monday)
Issued At 1114 AM MDT Sun Aug 13 2017

Areas of MVFR and even IFR cigs across western SD east of the
Black Hills will slowly dissipate this afternoon...but there may
some redevelopment tonight. Some TSRA may develop over northeast
WY into far southern SD this afternoon and tonight with local MVFR
conditions.

&&

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

$$

DISCUSSION...15
AVIATION...Johnson



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