764 
fxus63 koax 030858 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
258 am CST Wednesday Dec 3 2008 


Discussion... 
precipitation is moving into eastern Nebraska this morning as upper trough drags much 
colder air into the plains. Subjective 00z upper air analysis 
indicates deepening upper trough across WY/co/UT...with ripples in 
the flow in western South Dakota...AZ...and Nevada. Upper-level jet streak was 
digging behind the trough...with up to 135kt in northern British Columbia...and with 
exit region of jet diverging/branching across the ctrl plains. 
850mb cold front was located from northern ont through southeastern Minnesota/northwestern 
Iowa/eastern Nebraska...then wswd through KS/cy/UT. Strong temperature gradient 
across the front was noted...with 13c at klbf/11c at koma and -5c at 
krap/-6c at kabr. Band of snow in response to frontogenetic forcing 
extended from ctrl Nebraska through southeastern South Dakota into southern Minnesota at 08z...with a 
lighter band of reflectivities across S ctrl to eastern Nebraska that was 
struggling to reach the ground. Surface cold front was well through the 
County Warning Area at 08z...with surface low centered in S ctrl Kansas as well as in northern 
ont and cold front extending between the two. Winds in ctrl Nebraska 
were gusting as high as 30-40+ miles per hour behind the front. 


Main forecast challenge lies in precipitation today. NAM has struggled to 
capture ongoing precipitation trends...thus have leaned more toward the 
GFS. Northern snow band was tied fairly closely to 700mb fgen...while 
southern band struggling to reach the ground was tied to 850mb fgen. 
Saturation improves further back into the cold air...thus northern band 
has been more productive with snow...with visible as low as 3/4 Michigan in 
South Dakota. Expect strongest 700mb fgen to diminish from the northern County Warning Area and 
intensify across the ctrl County Warning Area by 12z as baroclinic zone pushes 
through the region. Though ongoing band in ctrl Nebraska is struggling 
to reach the ground...it is likely contributing to saturation of the 
column by persistent lifting. Thus...think ctrl to southern County Warning Area will 
still see a few hours of lt snow this morning. Have pushed probability of precipitation northward in 
12-15z window. Have also pushed probability of precipitation out faster after 15z and 
especially after 18z as fgen forcing pushes out of the County Warning Area and less 
favorable q-vector field overspreads the area. Did hold onto flurry 
mention behind the snow as low-level lapse rates increase under cold 
air advection. Models depict a reinforcing shot of cold air 
accompanying a shortwave moving through the back side of the trough 
on Thursday morning...with quantitative precipitation forecast just NE of the County Warning Area. Low-level lapse rates 
remain steep through Thursday...but with dry profile in place atop very 
shallow low-level moisture...think it will be tough to squeeze out 
measurable snow. Have backed off probability of precipitation in all but nernmost County Warning Area 
06-12z Thursday...and removed altogether 12-18z...with flurry mention 
through the day Thursday. Kept diurnal spread of temperatures today very low 
with strong cold air advection and persistent clouds...and also 
kept temperatures on the cool side Thursday /particularly in the northern-northestern 
County Warning Area/ as reinforcing cold air moves through and potential for 
lingering clouds persists. 


Surface high is prognosticated to pass through ctrl plains near southern County Warning Area on 
Thursday nt/Friday morning as conditions clear...setting up more ideal 
radiational cooling. Continued to indicate mins Friday well below 
guidance...and will need to watch any areas that end up with snow 
cover from today/S event for pockets of stronger cooling. Return 
flow becomes established briefly on Friday before yet another clipper 
moves through the plains/Midwest on Friday nt/Sat. Kept County Warning Area dry for 
now with this clipper...though a stray snow shower could sneak into 
the County Warning Area if clipper dives a bit further south than current forecasts. 


Made no changes beyond Sat. 


&& 


Aviation... 
for taf sites kofk/koma/klnk through 04/12z. 


A band of snow in northeast Nebraska will move south through the early 
morning. IFR visibilities in snow are likely for a few hours as this band 
passes through Oma and lnk around 12z...with IFR already observed at 
ofk. After the snow band passes...expect MVFR ceilings through 18z. After 
18z expect surface winds to back and diminish with ceilings slowly lifting 
to low end VFR. Winds will increase somewhat from the northwest and ceilings 
may lower to MVFR after 06z tonight as a weak clipper drops from the Dakotas 
into southern Minnesota and brings another push of Arctic air into the area. 
Also expect scattered light snow shower. 


&& 


Oax watches/warnings/advisories... 
NE...none. 
Iowa...none. 
&& 


$$ 


Mayes/pollack