Weather

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Area forecast discussion 
National Weather Service Aberdeen South Dakota 
1110 PM CDT Wednesday Aug 27 2008 


Update... 
have updated this evenings grids to account for isolated showers 
and thunderstorms over the southwestern County Warning Area. 


New aviation discussion below. 




&& 
Previous discussion... 
short term...through Saturday morning 


Surface high pressure moving northeast allowing stalled cold front 
to nudge its way northwards. Meanwhile...broad upper trough with 
embedded shortwave resulting in mainly middle/high clouds to spread 
across the western Dakotas. With shortwave nearing warm front 
seeing surface based thunderstorms closer to fsd County Warning Area...although southeast 
corner of County Warning Area seeing temperatures into middle 70s/dew points to low 60s so 
could see additional surface based development there. Also...with 
700 mb flow becoming southerly north of surface warm front...could see 
some elevated development to Katy/keth. 


Upper trough persists across the County Warning Area overnight. Despite steepening 
middle level lapse rates/middle level frontogenisis...dry sub cloud layer 
6-8kft thick will limit any precipitation to the odd sprinkle. 
Surface high moves out of northern rockies for Thursday and 
persist through Friday. Will see fast moving front across County Warning Area 
late Friday...however upper support for this feature remains too 
far north of the County Warning Area to suggest the inclusion of any probability of precipitation. 


Temperatures will remain seasonally cool with 850 mb temperatures 
only in the teens until late Friday. Late Friday and early 
Saturday warmer air from The Rockies will begin to return 
northwards. 


Long term...Saturday through Wednesday 


Medium range models are doing pretty good at least in the near 
term. Again the difference is in the details which will be 
difficult to resolve. Either way it looks like precipitation late 
in the extended period is a good bet. In the near term of the 
extended an 500 mb upper level trough digs along the West Coast of the 
United States. A Lee side trough forms along the Front Range 
Sunday with a southerly wind developing to bring warmer moist air 
into the area. The trough eventually moves east with the GFS 
closing off an 500 mb upper level low early Monday. The European model (ecmwf) closes 
off a low that cuts off and slows and deepens. Of importance to 
the forecast is when the upper level energy moves east and pushes 
the surface system through. Tried to leave some wiggle room for 
upcoming shifts. Kept with the idea of precipitation onset late 
Sunday night. If the European model (ecmwf) verifies this will be a little early. 
Also continued the mention of precipitation through the rest of 
the period. While this event has the potential to be a significant 
event it will take some time and some model convergence before 
confidence will improve enough to hit this hard. 




&& 


Aviation... 
an isolated shower or thunderstorm may affect kpir until 06z 
tonight. Otherwise expect VFR conditions for the rest of the 
evening at all terminals. Winds are expected to increase tomorrow 
afternoon at kpir and kmbg were gusts may rest 30 miles per hour. 


&& 


Abr watches/warnings/advisories... 
South Dakota...none. 
Minnesota...none. 
&& 


$$ 
Update...South Dakota 
short term...Connelly 
long term...Keefe 
aviation...South Dakota 


Weather.Gov/Aberdeen