265 
fxus63 koax 050721 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
221 am CDT Sat Jul 5 2008 


Discussion... 
thunderstorm chances through Tuesday remain the primary forecast 
concerns. 


Isolated storms developed this morning...shortly after midnight...in 
plume of increasingly higher Theta-E air in central Nebraska. Some 
of those storms will likely affect western parts of the County Warning Area this 
morning. Storms will end by noon as warm advection regime shifts 
northeast ahead of strong shortwave rolling east along the Canadian 
border. Resultant lowering surface pressure in the Dakotas will 
tighten pressure gradient across our area...causing brisk southerly 
winds and increasingly warmer 850 air. Combination of sunshine... 
mixing and warmer low level air should push temperatures toward 90 in much 
of the County Warning Area this afternoon. 


Thunderstorms are expected to fire in the central Dakotas later in 
the day as moisture advection surges north ahead of surface low 
pressure. Those storms should propagate southeast overnight as 
southwest 850 flow feeds eastward moving lines...with some storms 
possible into northeast Nebraska after midnight. 


Any storms that do make it into our County Warning Area should dissipate Sunday 
morning...but result will be strengthening baroclinic zone across 
eastern Nebraska. Both NAM and GFS show this...and both push surface 
dew points to or above 70f Sunday afternoon. Although low level 
convergence will be weak with minimal 0-6km bulk shear... 
surface-based convective available potential energy will exceed 3000 j/kg. Expect some pulse storms 
to get going in this juicy environment...especially in areas near 
surface convergence where temperatures just south should easily top 
90 and break weak cap. 


Perhaps best chance for organized storms will come Monday when GFS 
and NAM show more significant middle level cooling with a shortwave 
dropping into the plains. Surface dew points will still be near 70 
with bulk shear increasing with approaching wave. Again sbcapes 
will top 3000 j/kg with no cap. Low level convergence should be 
enhanced as induced surface low travels northeast along frontal 
boundary...so should not have a problem getting things going in 
the heat of the afternoon. Storms will shift southeast with time 
overnight on back side of exiting upper trough/surface low with a 
lingering storm possible Tuesday morning in southeast Nebraska. 


The rest of the forecast was left basically unchanged for now. GFS 
shows a relatively cool period Tuesday and Wednesday with highs 
slightly below normal. We could see another round of storms 
Wednesday night or Thursday as warm advection regime in return flow 
overspreads the region...but will not introduce just yet. 


&& 


Aviation... 
for taf sites koma/klnk/kofk through 06/12z. 


Theta-E advection underway with altocumulus castellanus from around Blue Hill (kuex) to 
west of Neligh. Profilers/vwps have 30 to 40kts at 850 mb and 
beginning to see some returns just west of the County Warning Area. Theta-E 
advection will continue overnight and this morning shifting 
eastward with time across eastern Nebraska and western Iowa along with the moisture 
axis. Expect VFR ceilings and possibly some local IFR/MVFR ceilings with 
the shra/tsra. Since there is a large focus area have cumulonimbus in the 
ofk/lnk tafs through 14z and may need to add to the Oma taf. Freezing 
levels are high and storm motions are weak...less than 10 kts...so 
should one of the storms go over a site...visibilties could drop to 
the IFR/LIFR range. Surface winds increase to 15 to 30kts after 14z and 
this should help mix the clouds out to scattered for later in the 
afternoon. 


&& 


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


$$ 


Discussion...dergan 
aviation...zapotocny