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fxus65 krev 221039 
afdrev 


Area forecast discussion 
National Weather Service Reno Nevada 
240 am PST Sat Nov 22 2008 


Short term... 


Fog has yet to develop in the Truckee area...however with 
temperatures now dropping to the dewpoint some patchy morning fog is 
still possible...and would lift quickly after sunrise. A short wave 
nearing the northwest coast will move across the Pacific northwest through this 
evening. Clouds and some light showers are located ahead of the wave 
this morning over northwestern California-southwestern or. Most of the energy will remain 
north of our County Warning Area...however the southern extent of the wave will move over 
northern California/northern Nevada later this morning into early afternoon. Enough energy 
and moisture may exist to generate a few light showers north of 
Gerlach in Nevada and into the Surprise Valley 15z-21z. Models are 
still not indicating much moisture below 700 mb making it much 
further south than the Oregon border...and even sref guidance for 
6-hour probability of precipitation are only 10-20% right along the Oregon border. The slight 
chance for showers was left in the forecast for northern Washoe County 
and the Surprise Valley...but removed for northern Lassen County. 


This system may should also increase winds a bit and help to mix out 
valley inversions at least north of Interstate 80. Highs on Friday 
only reached the middle 50s across western Nevada which is what the GFS 
guidance was advertising...so the amount of mixing we see today will 
have a great affect on temperatures. If winds do not pick up in the 
Reno area we may not reach much above the middle to high 50s. Where the 
GFS may be too cool if inversions mix out...the NAM is likely way 
too warm. Therefore used a blend and lowered temperatures today only 
a degree or so. 


A ridge builds over the area tonight through Monday ahead of a 
developing trough in the eastern Pacific. Flow will turn more southerly 
Sunday and Monday ahead of this system which will bring gradually 
warming temperatures. The GFS...NAM and sref are hinting at a better 
chance of some showers developing in the Sierra by Monday 
night...therefore a slight chance was added to the forecast along 
with increasing cloud cover starting Sunday night. Gmcguire 




Long term...Tuesday through Friday... 


Medium range models have developed more acute differences for this 
forecast cycle with European model (ecmwf) appearing as an outlier through much of 
the forecast. 


At the outset of the extended period GFS and Canadian remain more 
progressive than European model (ecmwf) with closed low dropping into southern/central California 
then opening rather quickly and spreading east on Tuesday/Tuesday 
night. With ridge to the east and fairly deep trough over the Midwest 
and Great Lakes...not completely convinced low in California will open quite 
that fast and move east. Still...ensembles do show moderate or 
better support for this idea. Can not discount completely but also 
not ready to up probability of precipitation for Tuesday. By Wednesday European model (ecmwf) shows low over the Great 
Basin while GFS is building a short wave ridge into the region. This is 
rather brief though as GFS drops another closed low into the region on 
Thursday. 


This low seems a bit more reasonable but significant differences 
then develop as European model (ecmwf) tries to build a highly amplified ridge into 
the West Coast by Friday as GFS hangs on to the low over the Great 
Basin. Consequences for the forecast range from dry by Friday if the 
European model (ecmwf) is correct to an extended period of cool showery weather if 
the GFS is correct. With little consensus...except better support 
from gefs ensemble suite for the GFS solution long term...am 
inclined to leave most of the extended forecast as is and only make 
minor tweaks such as lowering snow levels. Will not make much in the 
way of changes to probability of precipitation and temperatures. Only lowering snow levels a few 
hundred feet here and there as showery type precipitation should result in 
occasionally lower levels even with temperatures in the 40s. Mlf 
&& 


Aviation... 


VFR conditions will continue through Saturday. Areas of haze will 
still be possible at times vicinity ktvl. Patchy fog also possible 
at ktrk early this morning. Mlf 
&& 


Rev watches/warnings/advisories... 
Nevada...none. 
California...none. 
&& 


$$ 


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