673 
fxus63 koax 110826 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
325 am CDT Sat Oct 11 2008 


Discussion... 
..main forecast challenges are timing of heavy rain...And 
temperatures... 


Main feature on the 07z surface analysis was the rather sharp 
frontal zone extending from 1005mb low over the southwest corner of 
Kansas to a 1013mb low just west of Sioux Falls. The difference in 
the two airmasses was remarkable both in the temperature and 
relative humidity. Magnitude of baroclinicity is perhaps the 
strongest of the season for this region...with a temperature 
gradient as high as 12f across 18 miles...based just on available 
surface observation. Surface temperatures were in the 30s in north central 
Nebraska at Ainsworth...and lower 60s from Aurora to Columbus. 
Dewpoints were in the middle 50s across southeast Nebraska. 


At 850 mb...kuex radar vwp wind was 50 knots out of the southwest 
with laps 850 temperature of +15c. This compared to the klnx radar 
vwp wind of 15 knots out of the northeast and a laps 850 temperature 
of +8c. This highlights the wide range of highs that will occur 
today across Nebraska...as well as the kinematic differences in the 
warm vs. Cold sectors. 


The strengthening region of baroclinicity...or frontogenesis... 
resulted in a NAM forecast of strong enough ageostrophic circulation 
to squeeze out a few showers this afternoon near the Missouri 
River. Although it will certainly become cloudy from this vertical 
motion...believe the deeper moisture profile is too dry for rain 
until late afternoon and mostly confined to west of 
Lincoln-Wayne. 


Moisture is prognosticated to slowly increase throughout the weekend as 
sub-tropics become tapped with strengthening middle and upper level 
flow ahead of deep long-wave trough over western US. Watervapor loop 
shows this moisture has already reached the Texas Panhandle. The 
general scenario predicted remains consistent with the past few 
days. The upper trough slowly moves east with pockets of shortwave 
energy...a fairly strong jet...and the active frontal zone producing 
lift along and ahead of it. Overall pop forecast changed little... 
with 80+ probability of precipitation going Sunday afternoon into Monday. 


Timing of the heaviest rain still looks to be tied to the 
frontogenetical forcing that is maximized Sunday night...same time 
moisture transport is strongest just above the frontal zone. 
Widespread rains well over one inch seem likely. This could linger 
into Monday in the eastern counties...but slowly decrease with time 
Monday from west to east. 


Temperatures are tricky today through Tuesday. Again...anywhere 
along the frontal zone could see swings of 10-15 degrees...while 
warm sector will be subject to middle-teens 850 temperatures and strong 
mixing. Went a few degrees warmer than guidance deep in the warm 
sector...ie from Omaha south and east...and a few degrees cooler 
than guidance in the cold air mainly northwest of Norfolk. As the 
cold airmass moves south on Monday...temperatures will struggle to 
climb at all and may instead fall during the afternoon...especially 
if it rains all day. 


&& 


Aviation... 


For taf sites koma/klnk/kofk forecast valid through 12/06z. 


Outlook is VFR prevailing all sites through the period. Kofk though may see 
occasional MVFR ceilings at or below fl010 by the way 09z-12z this morning as surface boundary 
moves into NE Nebraska. Do not expect surface boundary to cross through taf sites 
during the period and should remain generally from southeastern South Dakota-southwestern Nebraska. 


&& 


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


$$ 


Nietfeld/Dee