346 
fxus63 kabr 240237 
afdabr 


Area forecast discussion 
National Weather Service Aberdeen South Dakota 
937 PM CDT Wednesday Jul 23 2008 


Update... 
the thunderstorms have diminished across north central South Dakota this 
evening and believe the severe threat has diminished. Thus...have 
cancelled the watch. Through the rest of the night...thunderstorms 
are still possible as there is a weaker low level jet along with warm air advection and 
elevated cape. Lowered chances some through the night across the 
County Warning Area. 




&& 
Previous discussion... 
short term...tonight through Thursday night 
thunderstorms beginning to develop over the Black Hills this 
afternoon with cumulus development farther north across the western 
Dakotas along a dry line. Dewpoints near 70 noted across the 
western counties this afternoon with low 50s dewpoints west of the 
dry line. Expecting additional development across western and 
eventually into central South Dakota later this afternoon and into 
the evening hours. Cloud cover across the east has kept 
instability at Bay and will await low level jet development overnight for 
any possible thunderstorm activity. Laps data showing 2000-2500 
j/kg cape across western Corson and western Dewey counties with no 
cap. Convective available potential energy drop off significantly east of the Missouri where cloud 
cover was present all day. High precipitable waters  from 1.50 to nearly 2 inches 
this evening indicates potential for heavy rain with any 
thunderstorms that develop. Best instability this evening lies 
along the Missouri River valley...with elevated instability 
developing later tonight across the east as low level jet strengthens. All 
in all...a rather difficult convective forecast this 
evening/overnight thanks in part to the cloud cover today. Did 
back off from the likely probability of precipitation across the east and went with 
generally 40 to 50 percent chances. Could see additional 
thunderstorm activity tomorrow afternoon as the actual frontal 
boundary moves through the area. By Thursday afternoon cape values 
approach 2000-2500 j/kg across the eastern County Warning Area. Decent shear 
values also reside across the eastern counties. Bumped up probability of precipitation 
slightly out of the slight chance category. Frontal boundary looks 
to exit the area to the southeast by Thursday evening but will 
maintain slight chance probability of precipitation near the front into Thursday evening. 


Temperatures will stay on the warm side tomorrow as 850 mb temperatures increase 
slightly. With more sunshine expected...will see highs approaching 
90 degrees in some areas Thursday afternoon. 




Long term...Friday through Wednesday 


Trends in upper level flow during this period can be defined as 
generalized ridging in the west with upper trough in the 
east...marked by several shortwaves traversing this flow. With 
little Faith in guidance ability to handle subtle features with 
this type pattern...have focused eliminating precipitation during several 
periods and in certain areas...however am having difficult time 
not adding slight chance/chance across much of the region over the 
length of the period. Have also made minor adjustments to 
temperature trends over mav/mex guidance for western counties as 
recent wet trend will skew forecast maximum guidance based off a drier 
climatology. 




&& 


Aviation... 
expect mostly MVFR ceilings through the night at abr and aty as 
the low level moisture remains high. Otherwise...scattered showers 
and thunderstorms are still possible through the night across the 
region and may affect the taf sites. Otherwise...the low clouds 
will move out of the eastern County Warning Area with drier air moving in later 
tonight through Thursday morning as winds become west to 
northwest. 










&& 


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


$$ 
Update...mohr 
short term...tmt 
long term...Connelly 
aviation...mohr 


Weather.Gov/Aberdeen