634 
fxus63 koax 061945 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
245 PM CDT Monday Oct 6 2008 


Short term...tonight through Thursday. 
Latest WV satellite loop showed upper wave lifting out of north central 
Kansas at 18z with showers on the increase across eastern Nebraska 
and southwest Iowa. Surface front was just starting to push into the 
area and extended from eastern South Dakota through central Nebraska 
and western Kansas. Surface wave was located along the front over 
north central Kansas. System is expected to move slowly east tonight 
with both GFS and NAM showing the front over central Iowa by 12z 
Tuesday with most of the rain ending during the morning in the far 
eastern portion of the County Warning Area. Will continue with the high probability of precipitation currently 
in forecast for tonight with a more rapid end to the rain on Tuesday 
as models show strong drying on the backside of the trough. 
Temperatures become main focus after Tuesday as more zonal flow 
develops across the region with trend toward a met/mav blend. Next upper 
trough comes into the western Continental U.S. Late in the period on Thursday 
with surface gradient increasing over the plains as Lee side low 
develops over eastern Colorado. 


Extended period...Thursday night through Monday. 


Uncertainty in the extended forecast has improved little from 
yesterday...and remains very high. The forecast hinges on a large 
upper trough digging into the western U.S. And then ejecting 
northeastward over the weekend. Models now agree on keeping this 
trough somewhere in the western U.S. However...this does not help 
much as strong gradients set up to the east of the upper trough in 
our general region. 


Models do suggest that a return flow regime will prevail by Thursday 
night. By Friday a cold front/inverted trough will set up somewhere in west 
or central Nebraska...possibly reaching northeast Nebraska. From this point 
on...GFS lowers heights more than European model (ecmwf) in central U.S. And 
consequently takes surface front farther east. 12z op GFS is behaving a 
lot better than yesterday. This still leaves a lot of uncertainty about 
the slow progress of the front through the area. With much cooler 
air and higher probability of precipitation on the west side of the trough...have generally 
kept a temperature gradient from west to east with better probability of precipitation in the north. 
This represents an attempt to translate HPC frontal positions into 
graphical fields. However...probability of precipitation will certainly need to be raised 
when it becomes more evident which periods the front will be active 
in the area...and whether a closed surface low moves north along the front. 
Overall chance of rain during the period looks quite high...and heavy rain 
is possible...despite lower probability of precipitation spread out over many forecast 
periods. There seems to be a decent chance that cooler and drier 
air will penetrate the region by Monday so kept it dry for now. 


A quick look at the new 12z European model (ecmwf) shows that it generally supports 
the previous HPC solution. While confidence remains low in later 
periods...will move probability of precipitation somewhat to the northwest Friday into Saturday. 


&& 


Aviation... 
for taf sites koma/klnk/kofk through 07/18z. 


Surface boundary extending NE-SW over central Nebraska will slowly move east into 
eastern Nebraska by the way 00z-03z and be the focus for prevailing MVFR conditions/-shra 
through about 12z all sites. Frontal passage/wind shift from S to northwest expected 22z 
kofk/06z koma/04z klnk...with potential crosswind threat at time of 
frontal passage. Passing rain showers may result in brief IFR ceilings/visible mainly by the way 
02z-08z...but have opted not to include in taf due to low 
confidence. 


&& 


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


$$ 


Fobert/pollack/Dee