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


Discussion...current surface analysis shows low pressure remaining 
over far southeastern Montana...with trough stretching southward across 
eastern Wyoming. Cold front is located further west across central Montana and 
northwestern Wyoming. Upper level analysis has low pressure over southern 
British Columbia...with trough covering much of the Pacific northwest. Skies are clear to 
partly cloudy across the area...with a few showers and storms moving 
across eastern Montana and into western ND. A tight pressure gradient 
across the South Dakota plains is resulting in breezy conditions east of the 
hills. Temperatures remain warm across the area...60s and lower 70s. 
Dewpoints are in the 50s and lower 60s ahead of the surface trough and 
in the 30s and 40s behind it. 


A hot day is on tap across the area ahead of the cold front...with 
highs in the 90s across the plains...80s in the hills. Gusty 
southerly winds will persist across eastern portions of the County Warning Area 
today...especially central South Dakota. Surf trough will make its way into far 
western South Dakota later today...switching winds to the west and southwest 
and bringing drier air in. The lowest humidities will be across 
the southwestern County Warning Area. With winds picking up in the afternoon across 
southern Campbell County in Wyoming...conditions will approach red flag 
criteria in that area. However...am not planning to issue a red flag 
warning at this time...as it looks like the winds will not quite 
reach criteria levels there. 


Chance for storms will generally hold off until tonight...mainly 
during the overnight hours...when cold front crosses the area. Upper 
low will move quickly east along the US/can border today and 
tonight...with bulk of upper level energy staying north of the County Warning Area. 
With the low remaining so far north...dry airmass over our area will 
also limit storm chances. Have kept storm chances limited to 
northern half of forecast area...with main chances likely to be 
across far northwestern South Dakota and points to the north after midnight. 
Threat for severe storms should stay north and west of the County Warning Area. 
Gusty northwest winds will develop behind the front late tonight. 


Gusty northwest winds will persist into Friday...especially across 
northwestern South Dakota during the morning and early afternoon hours. Much 
cooler air will be in place...with highs only in the 70s to middle 
80s...warmest across far southern South Dakota. Will see some puffy cumulus 
clouds around across the northern County Warning Area...but should be little or no 
threat for showers with drier air in place. Saturday will remain on 
the cooler side before temperatures warm back up late in the weekend. Highs 
on Saturday will mainly be in the upper 70s to lower 80s. 


Extended...warmer than normal temperatures will return for the 
extended forecast period as an upper level ridge builds over the 
northern plains. Models continue to show ll moisture and instability 
increasing west of the surface high over portions of northeastern 
Wyoming and western South Dakota on Sunday/Monday aft/eve...although 
it looks like the capping inversion will be strong enough to limit 
any thunderstorm development to over and near the Black Hills. Dry 
weather then expected again for Tue/Wed. 


&& 


Aviation...there is a chance of thunderstorms over portions of 
northeastern Wyoming and northwestern South Dakota from late this 
afternoon through tonight. Otherwise VFR conditions are expected 
through the aviation forecast period. 


&& 


Unr watches/warnings/advisories... 
South Dakota...none. 
Wyoming...none. 
&& 


$$