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Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota 
521 PM MDT Thursday Aug 21 2008 


Discussion...cold front currently positioned over southeast 
Montana and north central Wyoming will sweep across the County Warning Area tonight. 
Gusty northwest winds will develop behind the front. With strong 
cold air advection and 850 mb winds around 55 kts have decided to issue a Wind 
Advisory for northwest and west central South Dakota from 6z to 
12z Friday. Have tweaked grids for stronger winds across these 
areas. The rest of the forecast is on track. 


&& 


Previous discussion... /issued 250 PM MDT Thursday Aug 21 2008/ 


Discussion...20z surface analysis shows a surface low across far 
southeastern Montana...and a cold front across central Montana 
pushing toward the County Warning Area. Breezy southerly winds were across south 
central South Dakota. Highs have reached the 90s across the 
plains...with kphp reporting 97 in the last hour. 


Tonight...cold front will continue to push southeast as an upper low 
crosses the Canadian rockies. A shortwave moving across southern 
Montana will approach the area...swinging into North Dakota and just 
missing the County Warning Area. Models have been indicating the development of a 
squall line across eastern Montana moving into western North Dakota 
this evening. With a well mixed boundary layer up to 10kft or 
higher...severe winds are likely a threat with a bowing line. It is 
possible that the southern tail end of this line will affect far 
northwest South Dakota...so will leave in chance probability of precipitation overnight and 
along northeast Wyoming for earlier convection late this 
afternoon/early evening. The front will quickly push through the County Warning Area 
tonight reaching krap around 06z with gusty northwest winds behind 
it. Models have showed some indication of borderline advisory 
criteria winds...but since the winds will not last more than three 
hours...will not issued an advisory. 


Much cooler air will also filter in behind the front which will 
bring significantly cooler highs Friday. Skies will become mostly 
sunny Friday as an upper ridge builds across the western Continental U.S.. the 
ridge axis will move through the northern plains Saturday keeping 
quiet weather around and skies mostly sunny across the region for 
the first half of the weekend. 


Extended...an upper level ridge over the region on Sunday and Monday 
will keep above average temperatures over the area. Models continue 
to show some low level moisture and instability over the Black Hills 
and portions of southern South Dakota both days along with a weak wave moving 
through. Therefore...will keep low probability of precipitation over the Black Hills along 
with spreading the chances easterly into south central South Dakota. 
Models push a trough through the region towards mid-week. This will 
bring a daily chance of thunderstorms for various parts of the area 
from late Tuesday through Thursday...along with slightly cooler 
temperatures. 


Aviation...a cold front will push through the area this evening 
bringing gusty northwest winds into Friday...particularly over the 
South Dakota plains. Isolated to scattered thunderstorms and rain will be possible tonight over 
parts of northeast Wyoming and northwest South Dakota...with MVFR 
visible in the heavier precipitation. Otherwise...VFR conditions will prevail. 


&& 


Unr watches/warnings/advisories... 
South Dakota...Wind Advisory from midnight tonight to 6 am MDT Friday for Butte- 
Custer Colorado plains-Haakon-Harding-Jackson-northern foot hills- 
northern Meade Colorado plains-Pennington Colorado plains-Perkins-Rapid 
City-southern Meade Colorado plains-Sturgis/Piedmont foot hills- 
Ziebach. 


Wyoming...none. 
&& 


$$ 


Wetenkamp