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Area forecast discussion 
National Weather Service Aberdeen South Dakota 
716 PM CST Tuesday Dec 2 2008 


Update... 
have sent out new zones to extend the Snow Advisory east to the 
Minnesota border. Radar continues to show some banding that could 
drop advisory criteria snow along the south east counties in this 
area. 


&& 
Previous discussion... 
short term...tonight through Thursday night 
main forecast challenge in the short range is precipitation tonight...and then 
temperatures and clipper waves the rest of the period. It appears that 
many ingredients are coming together for a quick burst of snow 
over the southwest County Warning Area this evening. Both NAM/GFS show strong middle 
level 2d frontogenesis passing across this region. Potential coupling 
of the 300 mb jet will also likely add to enhanced uvm from 00-03z. 
Bufr soundings and time heights show strong but short lived lift 
at kphp/kpir/k9v9 through the favored snow growth region. 
Meanwhile soundings also indicate that low level dry air will cool 
off and saturate the column quickly once precipitation starts. So even 
though a short period of time with mixed precipitation could occur...will 
go with dominant type and just mention snow in the forecast. 
Earlier issued Winter Weather Advisory still looks on track for 
timing and areal coverage...so no changes planned at the moment. 
Looking ahead...we maintain very steep middle level lapse rates both 
Wednesday and Thursday under cold air aloft. Despite the influx of 
fairly dry air...will likely still see flurries or snow showers 
both days. For Wednesday night I did beef up probability of precipitation. Models are 
showing another clipper dropping through the forecast area...and 
both the GFS and NAM are more bullish on precipitation. Saw no reason to 
object to these latest developments...so upped probability of precipitation along with 
adjacent offices. As for temperatures...it is certainly looking 
chilly through the next couple days as Arctic air oozes into the 
area. Still feel that guidance is a bit on the high side both Wednesday 
and Thursday...but especially on Thursday where 850 mb temperatures will 
struggle to reach higher then -15c. So stayed a bit under the mav 
guidance for highs both days. 


Long term...12z Friday through Tuesday 
main forecast challenge revolves around precipitation potential for 
Friday/Friday night...and again for Sunday/Sunday night. 


County Warning Area remains under a general well established northwest flow pattern for 
the extended. Lead wave exits the County Warning Area at the beginning of the 
extended...with general downglide/subsidence in place Friday 
morning. The next weak clipper system drops quickly through late 
Friday afternoon and Friday night...with next shot of trailing 
cold air advection. The ec and GFS differ with the surface features Friday 
night...with the 00z ec closing off a surface low with the GFS keeping 
more of an open trough sliding through. Inherited grids had slight chance 
probability of precipitation for the period...and with cold air and minor forcing...might 
be able to squeeze out a flurry or two...so kept small probability of precipitation in for 
Friday aftn/overnight. 


Upper level ridging then slides quickly through for 
Saturday/Sunday ahead of next Pacific northwest system moving into northern 
rockies. The models are still differing in their exact solutions...but 
in general agree with 500 mb wave dropping into County Warning Area Sunday night into 
Monday. By 12z Monday...both ec and GFS hint at a potential 
overrunning event with good warm air advection ahead of surface low with low level 
cold air already in place. Have gone with low chance probability of precipitation for this 
time frame...and increased cloud cover accordingly. 


Temperature wise...HPC temperatures seemed a bit warm when looking at fcsted 850 mb 
temperatures...expected cloud cover for the weekend along with potential 
snow for the first part of next week. Undercut HPC temperatures by a 
category which seems a bit closer to latest 12z mex numbers. 


&& 


Aviation... 
IFR conditions in snow and fog are widespread across the area 
tonight. WSR-88D data would suggest the back edge of the snow is 
now moving into South Dakota but will keep snow falling until 
around midnight in the more southern counties. 


&& 


Abr watches/warnings/advisories... 
South Dakota...Winter Weather Advisory until midnight CST /11 PM MST/ tonight 
for Buffalo-Clark-Codington-Deuel-Dewey-Faulk-Grant-Hamlin- 
hand-Hughes-Hyde-Jones-Lyman-Potter-Spink-Stanley-Sully. 


Minnesota...none. 
&& 


$$ 
Update...Keefe 
short term...tmt 
long term...Hintz 
aviation...Keefe 


Weather.Gov/Aberdeen