Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 211716
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1116 AM MDT Fri Jul 21 2017

.UPDATE...
Issued at 1036 AM MDT Fri Jul 21 2017

Smoke from fires in central Montana is currently reducing the
visibility across parts of the region, especially in areas along
the northern Black Hills, foothills and adjacent plains. Have
added the mention of smoke in those areas for today.

&&

.DISCUSSION...(Today Through Thursday)
Issued at 222 AM MDT Fri Jul 21 2017

08z surface analysis had low pressure over southeast MT with
"cold" front into northwest WY and trough into central NE.
Convective complex moving east along trough early this morning.
Should be out of the CWA by 12z. Shortwave scooting across eastern
MT into the Dakotas will push surface low into eastern ND today
dragging "cold" front through the CWA. Much drier air will move in
behind the front with 20-30kt boundary layer winds. Expect deep
mixing given strong surface heating and weak cool air advection
from 800-600mb. Gusty northwest winds will result. Leftover
instability on tail end of shortwave may pop a few -TSRA in
central SD late this afternoon and early this evening. Clearing
skies are expected tonight. Temperatures will be above guidance
today and near guidance tonight.

Saturday and Sunday, upper ridge will rebuild over the Rockies as
westerly flow Saturday becomes northwesterly Sunday. Dry air in
place, so PoPs not warranted. Few breezy spots Saturday afternoon.
Temperatures will be near guidance.

Next week, upper ridge shifts into the plains and flattens. Series
of shortwaves moving across the US/Canadian border will push a few
frontal boundaries into the CWA, which may be the focus for
convection. Temperatures will peak early in the week and then cool
to near normal for the rest of the week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Saturday)
Issued At 1113 AM MDT Fri Jul 21 2017

Isolated thunderstorms will be possible this afternoon and evening
across central South Dakota which may result in localized MVFR
conditions. Smoke from fires in central Montana are reducing
visibility across portions of northeast Wyoming and far western
South Dakota and may result in occasional periods of MVFR VSBY.
Otherwise VFR conditions are expected.

&&

.FIRE WEATHER...
Issued At 222 AM MDT Fri Jul 21 2017

Much drier air will push into the area this afternoon. Minimum
relative humidities in the teens will be common across the
northwest. Deep mixing will promote gusty northwest winds across
far northeast WY and northwest SD. Critical fire weather
conditions will result, so will hoist Red Flag Warning.

Few breezy spots will occur again Saturday with minimum relative
humidities from 15-25%.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Red Flag Warning until 6 PM MDT this evening for SDZ261.

     Heat Advisory until 7 PM MDT /8 PM CDT/ this evening for SDZ032-
     043-046-047-049.

WY...Red Flag Warning until 6 PM MDT this evening for WYZ297-298.

&&

$$

Update...10
DISCUSSION...Helgeson
AVIATION...13
FIRE WEATHER...Helgeson



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