654 
fxus63 koax 211949 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
249 PM CDT Thursday Aug 21 2008 


Discussion... 
main forecast challenge will be the next frontal boundary moving 
into the area on Friday and its impact on local weather over the 
next few days. 


In the meantime...upper trough noted across the plains continues 
to shift east today with latest water vapor imagery/88d mosaic 
indicating all measurable precipitation remains well east of the County Warning Area. 
Lingering spotty drizzle has all but ended with just some clouds 
remaining across the region with temperatures in the upper 60s to middle 
70s. Feel that these clouds could scatter out a bit this evening... 
but then probably fill back in after midnight with some status 
developing by daybreak based on low level humidity forecasts. Was also 
somewhat concerned with fog development given only a degree or two 
temperature/dewpoint spreads. However...tightening pressure gradient in 
response to advancing front should help to keep the boundary layer 
mixed enough for most areas...except southeast Nebraska and 
southwest Iowa where areas of fog may develop...which could be 
locally dense in areas from kfnb to kicl...and possibly even 
locally at ktqe. 


Models are in pretty good agreement with the front moving from 
northwest to southeast Friday afternoon and evening. Healthy cap in 
place along and ahead of the front should hold off development 
until middle to late afternoon north of i80...then with decent precipitation 
chances Friday evening as cap weakens aloft. While instability 
appears modest...bulk shear is not that impressive resulting in 
scattered multi cells with just an isolated severe threat due to 
high freezing/wet bulb zero values. NAM/sref suggesting upwards of 
60 to 70 percent probability of precipitation while GFS only hinting at 20 to 30 percent 
probability of precipitation. Will go middle of the Road with a 50/50 chance with precipitation 
possibly lingering into early Saturday southern County warning forecast area. Temperatures ahead 
of the front could make a run at 90 due to warm tongue aloft and 
compressional heating. 


Beyond then...the forecast doesn't appear as clean as previously 
thought. The front essentially stalls just to our south across 
northern Kansas/Missouri. Given its close proximity to our 
western/southern areas with potential for weak impulses to move 
through the region...along with 850mb front remaining in the area... 
have decided to mention slight chance probability of precipitation Saturday night through 
Sunday...but tried to keep northeast County warning forecast area dry during this time. 


For the extended...based most of the forecast on HPC guidance 
which used a blend of various models and their ensembles. Went dry 
for Tuesday...but then included small probability of precipitation for Wednesday/Thursday 
as a couple of fronts move through the region. 


&& 


Aviation... 
for taf sites koma/klnk/kofk through 22/18z. 


Low level clouds and MVFR conditions will exist briefly early this 
afternoon due to continuing moisture advection into the region. 
Later this afternoon and evening...should see clouds begin to 
dissipate and VFR ceilings at all sites through the rest of the day 
into the early morning hours. A new frontal system will begin to 
move across our area early tomorrow morning with the Prospect of 500 
feet ceilings and IFR conditions at all sites by 11z. By 13z...VFR 
conditions are expected to return at all sites through the end of 
the period. 


&& 


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


$$ 


Forecast...Dewald 
aviation...Kurtz