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Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota 
300 am MDT Sat Aug 30 2008 


Discussion...current surface analysis places low pressure along the 
Saskatchewan/Manitoba border while high remains over the Midwest. 
Upper level analysis places Flat Ridge over the northern 
plains...with upper trough off the Pacific coast. 


For today...hot...windy...and dry conditions are expected across the 
area as thermal ridge intensifies. NAM and GFS continue to bring 
30+c 850 miles per hour temperatures over northeast Wyoming and western South Dakota. 
With the dry airmass in place...afternoon relative humidity values 
will generally be in the teens. Aforementioned trough will start 
pushing into the West Coast and intensifying while surface low 
stretches to the southwest with secondary low developing. With 
increasing pressure gradient over the area...southerly winds will be 
on the increase...particularly over the South Dakota plains. Will be 
going with a Wind Advisory over south central into parts of western 
South Dakota. With the atmosphere remaining mixed over south central 
South Dakota into the evening...will keep the advisory going 
overnight. Overnight temperatures will be warm...particularly over south 
central South Dakota and over the downslope portions of the northern 
Black Hills. 


On Sunday...aforementioned initial surface low will slide to the 
northeast with southern part breaking off and intensifying near the 
Monday-dak border. This will bring another windy day to the 
area...particularly over south central South Dakota. Aforementioned 
advisory will continue through the day into the early 
evening...through may have to be expanded in coverage to the west 
and push later into the evening depending on how well the atmosphere 
can remain mixed. In the late afternoon/evening surface low/frontal 
boundary starts pushing slowly to the east as upper trough continues 
to dig over the western Continental U.S.. first short wave sliding through 
southwesterly flow aloft will start sliding in bringing a chance for 
showers and thunderstorms to the western County warning forecast area. Strongest instability 
holds to the north...so if any storm were to become severe it would 
be over northwest South Dakota. A wide variety of low temperatures are 
expected with 50s over northeast Wyoming and 70s over south central 
South Dakota. 


On Monday...frontal boundary shifts slowly to the east with high 
temperatures dependant on the frontal position. For now...have gone 
with middle 60s over parts of northeast Wyoming and far northwest South 
Dakota...and upper 80s over south central South Dakota. Upper trough 
pushes over The Rockies towards the plains. This will bring showers 
to the area...particularly in the evening. Will keep isolated 
thunderstorms over much of the eastern County warning forecast area into the evening as 
forecast soundings continue to indicate elevated instability over 
that area. 


Extended...NAM/GFS/ECMWF in good agreement with upper trough swinging 
through the area Tuesday morning. Best chance of precipitation will 
come early...as best lift moves into North Dakota by afternoon. 
Surface cold front south and east of forecast early Tuesday. Cold 
advection and clouds will keep temperatures in the 60s for most 
locations. Surface high across the area Tuesday night with cool 
overnight lows. GFS/European model (ecmwf) show trough digging across the northern 
plains towards the end of the week...though some timing/location 
differences. Cool and unsettled weather expected for the end of the 
week. 


&& 


Aviation...clear skies will continue through today. Southerly winds 
will increase and be rather gusty across the South Dakota plains. 


&& 


Fire weather...hot temperatures and low humidities expected across 
the area today. Highs will be in the middle 90s to near 100 degrees 
across northeast Wyoming along with over western into south central 
South Dakota while minimum relative humidity ranging from near 10 
percent across northeastern Wyoming to around 20 percent across 
south central South Dakota. As a surface low develops to the 
west...gusty winds will increase with strongest winds on the plains 
of western and south central South Dakota. With fuels 
critical...have issued red flag warning late Saturday morning 
through Saturday evening. 


&& 


Unr watches/warnings/advisories... 
South Dakota...red flag warning from 10 am to 10 PM MDT Saturday for badlands 
area-northwestern South Dakota plains-southwestern South 
Dakota. 
... Advisory in effect for south central and parts of western 
South Dakota today through Sunday... 


Wyoming...red flag warning from 10 am to 10 PM MDT Saturday for lower 
elevations of Crook and Weston counties-northern Campbell- 
southern Campbell. 


&& 


$$