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Area forecast discussion 
National Weather Service Aberdeen South Dakota 
954 am CST Thursday Dec 4 2008 


Update... 
temperatures are struggling to warm today...with cold air advection in place 
coupled with the new powder that fell last night. Given that Sat 
pictures show band of clouds working into eastern County Warning Area...and clouds already 
persist in the west...not going to be a good warming day. Have 
knocked about a category out of highs...especially across the 
east...for today. Have also removed mention of flurries for the 
rest of the morning...as clouds have yet to advect in. With cold 
temperatures aloft...expect clouds to move in/develop across the 
east...so flurries still possible this afternoon. 


Updated aviation discussion below. 




&& 
Previous discussion... 
short term...today through Saturday 
good agreement with the models through the short term with the 
upper level flow and surface features to affect the County Warning Area. Expect it 
to be blustery today across the County Warning Area with cold air advection. Surface 
temperatures upstream of the County Warning Area were in the single digits early 
this morning. Models all show high low level relative humidity throughout the day 
in this cold air advection pattern. Thus...expect low clouds to move in/develop 
over the County Warning Area this morning with some scattered flurries as the 
cloud layer will be in the -15 to -20c range. Also...with the 
steep low level lapse rates and 20 knot 925mb winds...expect winds 
to be in the 15 to 25 miles per hour range across the County Warning Area today. With the 
cold air advection...new snow cover along with low clouds...it will be difficult 
for a lot of rise in the temperatures through the day. Highs 
should be mostly in the teens. 


For tonight and Friday...a surface high pressure area in the 
western part of the region will slide southeast of the region. 
This will result in the surface and low level winds turning from 
west/northwest to the south/southwest. These winds will bring in 
warmer and drier air across the County Warning Area tonight through Friday. 
Thus...expect the low clouds to break up or move out tonight from 
west to east with skies becoming mostly clear. With the new snow 
cover across most of the County Warning Area...the inversion is expected to form 
quickly with winds decreasing to less than 10 miles per hour most areas. 
Expect lows across the area in the single digits with maybe lower 
in the favored low spots if winds drop off enough. 


For Friday through Saturday...the models all show a surface low 
pressure area coming across southern Canada and then southeast 
across northern Minnesota and into the northern Great Lakes 
region. The warmer and drier air will be drawn into the low 
pressure area for Friday and Friday night. The models also show a 
decent surface pressure gradient developing for this time which 
would bring some breezy/windy south winds for Friday into Friday night. 
Temperatures will be tricky on Friday with mostly sunny skies and 
warm air advection over snow cover. Went with middle 20s to middle 30s at this point 
and may have to raise them even more. Otherwise...the models show 
the middle levels moistening up through the day with middle level warm air advection. 
The models also show some light quantitative precipitation forecast in the County Warning Area by 00z Saturday. 
Think some light snow could develop across the northern County Warning Area by 
late Friday afternoon and move east into northeast South Dakota and west 
central Minnesota through Friday night. Increased probability of precipitation across the area 
and mainly across far northeast South Dakota and west central Minnesota for Friday 
night. 


As the surface low pressure area moves off to the east Friday 
night and Saturday...winds will become northwest again with 
another shot of cold air advection through Saturday. Again with high low level relative humidity 
in this cold air advection pattern...expect low clouds to overtake the area again 
Friday night and Saturday. There also may be some flurries. May 
have to drop highs even more for Saturday. 




Long term...0z Sunday through Wednesday 


Forecast challenges include precipitation chances early in 
extended...and temperatures Sunday night and Monday. 


The period begins with a surface high pressure over Minnesota. The 
eastern half the County Warning Area should be pretty cold come Sunday morning 
with light winds and mostly clear skies. Middle level relative humidity values 
increase some as the night GOES on...as a weak short wave slides 
across the western Dakotas. HPC does give my western half of the 
County Warning Area about one inch of snow for Saturday night. Models have been 
fairly consistent with generating a band of qfp along the Missouri 
River so have increased probability of precipitation to low chance in that location. This 
short wave dives into eastern Kansas on Sunday as the surface high 
slides into Illinois. Most of Sunday may end up being dry as we 
wait for the next system to move into the region on Sunday night. 
Both the GFS and European model (ecmwf) indicated a warming trend developing late 
Sunday afternoon and continuing through Sunday night as a weak middle 
level ridge builds into the area with southwest winds. The European model (ecmwf) 
is showing Sunday night's lows only falling into the middle 
20s...while 0z mex guidance continues to show lows in the middle 
teens. Did increase lows some given the fact that 850 mb temperatures 
increase to +1 with good mixing winds and a weak Theta-E ridge 
poking into the County Warning Area. All this occurs ahead of a low pressure 
systems that drops into North Dakota. The balk of the 
precipitation appears to be across the eastern Dakotas and much of 
Minnesota. This low pressure looks to open The Gates to some 
Arctic air with 850 mb temperatures falling to -30c by Tuesday night. 




&& 


Aviation... 
widespread VFR ceilings through much of the am...however there will be 
brief periods of MVFR ceilings at or above 2kft as well. Winds will remain from 
the northwest with gusts to 25 miles per hour shifting out to the west this 
afternoon while dropping off. 








&& 


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


$$ 
Update...Hintz 
short term...mohr 
long term...South Dakota 
aviation...Connelly 


Weather.Gov/Aberdeen 

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