Weather

776 
fxus63 koax 112002 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
302 PM CDT Sat Oct 11 2008 


Short term...tonight through Tuesday. 
Beginning of a wet weekend is upon the area already today. 
Subjective 12z upper air analysis indicates upper low centered in 
Nevada...with 500mb heat falls up to 70m centered in northern Arizona indicating 
some digging still taking place. Upper jet is still strongest 
behind the low...with 130kt streak punching behind low. Quite a bit 
of upper-level divergence was evident over the ctrl plains...likely 
aiding with ongoing rain showers/thunderstorms and rain activity today. Low at 850mb was 
centered in Utah...with wavy warm front extending through Colorado/western Nebraska 
into eastern South Dakota. WV imagery and 850mb dewpoints indicate moisture 
flowing off Norbert over the Baja California peninsula...with moisture also 
flowing off the Gulf into Texas. Nose of 12c dewpoints reached into 
eastern Nebraska/western Iowa. Surface front at 19z extended from southwestern Kansas through 
khys/khsi/kbvn/kykn toward a secondary low centered in southwestern Minnesota. 
Rain showers/thunderstorms and rain have persisted northwest of a line from kolu to ksux. 


Main forecast concerns are in timing frontal passage and highest 
chances for precipitation...along with rainfall amts and onset times as well 
as impact on temperatures. Forecast for rain is certainly an easy call for sun 
through Monday nt...but as event nears...details in timing and extent 
of precipitation are becoming clearer. 00/12z European model (ecmwf) trended slower than 
previous runs...and 12z GFS has slowed as well...with NAM runs in 
line with slow solutions. Front is retreating into ctrl Nebraska/South Dakota and 
should drag most precipitation with it tonight out of eastern Nebraska/western Iowa...and 
have probability of precipitation tapering from likely in northestern Nebraska this evening to chance after 
midnight. Slow-moving front approaches the northwestern County Warning Area during the day 
sun...but makes little progress toward southeastern Nebraska until sun nt as main 
upper low lifts northeastward across the northern plains and helps drive it 
through. Have continued a rather tight pop gradient across the County Warning Area 
sun...with categorical in the northwest tapering to schc in the southeast. Bulk 
of precipitation looks to arrive between 00-12z Monday in northwestern half of 
County Warning Area...working through the County Warning Area through 12z Tuesday. Models are now more 
consistent in leaving a remnant upper low in the SW as the northern 
stream low ejects...and that remnant low will allow chance for rain showers to 
continue through Tuesday well behind the main front. Evolution of that 
upper wave is still uncertain...but will hedge forecast toward murkier 
side as models continue to depict a lingering system. Have 
continued trend of lowering maximum temperatures Monday and Tuesday...with cold air 
advection/nearly flow and clouds/precipitation allowing little if any warming 
on Monday and also holding back temperatures on Tuesday. 


Long term...Tuesday night through Saturday. 
System finally exiting the region Tuesday night will bring the 
only real chance for precipitation during the extended period. A 
dry and relatively mild forecast remains intact for the rest of 
the week into the weekend. 


Used the European model (ecmwf) for the base of the long term forecast grids. The 
European model (ecmwf) depicts a slightly more amplified upper pattern through next 
weekend as opposed to the more zonal look of the operational 00z 
GFS. While the trend the last couple of runs of the models has been 
toward less amplification over the Continental U.S....a plurality of the GFS 
ensemble members...and especially the European model (ecmwf)...are slightly more 
amplified with the upper air pattern by the weekend. The 12z GFS 
graphical forecasts have trended slightly toward the 00z European model (ecmwf) 
solution...lending some credence to the above reasoning. In sensible 
weather terms...this translates to slightly cooler temperatures 
Friday and Saturday as northwest upper flow drives cooler air from 
the northern plains in to our area. In fact...the 00z operational 
GFS is at the top of the ensemble MOS temperatures through the week. 
So have gone under the GFS MOS temperatures...but not drastically so. 


Upper trough on Tuesday will be exiting the area Tuesday night. 
Could see lingering showers in the southeast then...so have 
maintained a slight chance for showers. Our next potential 
weather-maker is a deepening shortwave trough dropping into the 
plains on Thursday as per European model (ecmwf) forecast. This system is forecast to 
track across South Dakota and Minnesota...keeping precipitation 
north of our area...and resulting in a cold frontal passage on the 
back side on Friday. Moisture looks to be limited in our area...so 
will maintain dry forecast. Have also maintained a relatively cool 
forecast of temperatures in the lower 60s...but could see these 
pushed a bit cooler with later runs if more amplified European model (ecmwf) solution 
is realized. 


&& 


Aviation...for taf sites kofk/koma/klnk forecast valid through 12/18z. 


Periods of MVFR conditions (10/11-12 18z-04z & 10/12 14z-18z) for 
kofk through the first half of the forecast period and then again toward the 
end of the period. Koma and klnk may see MVFR conditions toward the end 
of the forecast period (10/12 14z-18z). VFR conditions will otherwise... 
dominate most of taf sites through the forecast period. Some isolated 
thunderstorms are possible...especially in the next couple of hours 
across areas in and around kofk. The chance for rain continues through the 
period and will increase later in the period. 




&& 


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


$$ 


Mayes/dergan/Reese 

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