988 
fxus65 krev 212238 
afdrev 


Area forecast discussion 
National Weather Service Reno Nevada 
238 PM PST Friday Nov 21 2008 


Short term /tonight through Monday afternoon/... 
minimal concerns for this weekend into Monday with warm days and 
cold clear nights. Expect more fog to develop around Truckee early 
Saturday morning. 


One system will pass north of the area Saturday and bring clouds 
and a low chance of rain/snow along the Oregon border. System may 
also increase winds a bit and help to mix out valley inversions. 
Did not use the GFS high temperature guidance once again as the 
numbers have been several degrees low the last few days. NAM/NGM 
guidance high has been close to reality. 


Ridge builds over Nevada on Sunday ahead of a developing trough in 
the Pacific which turns the flow southerly. This will help 
maintain the warm high temperatures and light winds into Monday. 
Brong 


For Monday night through Wednesday night...the main changes to the 
previous package were to up probability of precipitation Tuesday and Wednesday based on 
the 12z ensemble probabilities of precipitation and the fact that the GFS 
and European model (ecmwf) look more alike in the large scale than in previous runs 
(although the devil will be in the details). 


An upper low near the California coast is now projected to be 
kicked inland by an upstream system and bring general troughing to 
the region starting Monday night/Tuesday. However...exactly when 
and where the smaller scale pieces within the trough wind up are 
dubious at this point. Therefore...I went towards the GFS 
ensemble/climatology concept which would bring a broad chance of 
precipitation to the Sierra...with a general slight chance to chance out 
into the Great Basin Tuesday through Wednesday. Details such as 
snow level or quantitative precipitation forecast amounts (although climatologically light is a 
good bet) are too uncertain to predict given the semi-cutoff 
nature of the system. Snyder 


Long term /Thanksgiving day and Friday/... 
medium range models continue to have differences among them in the 
latter half of the extended. On Thursday the GFS shows a deep 
upper low near 45n 130w. Instead of a deep low the European model (ecmwf) and the 
Canadian both show a weaker trough moving into the Pacific northwest. On 
Friday the GFS continues to show the deep low and has moved the 
center of it to just west of ksfo. The Euro however has a weaker 
low farther east over the Great Basin. 


These differences in strength...and especially location...of the 
respective systems lowers forecast confidence for temperatures and 
precipitation Thursday and Friday. Will continue with a slight 
chance of precipitation over most of the krev County warning forecast area for Thursday due to the 
differences in the model solutions. Both the Euro and GFS show a 
trough in the vicinity of the County warning forecast area on Friday. Even with the 
uncertainty in the location...the progressive atmospheric flow 
should bring the trough near our region. With this in mind have 
increased probability of precipitation to chance over much of the County warning forecast area. Probability of precipitation can be trended 
up or down as the evolution of this scenario becomes more clear. 
However this far out chance probability of precipitation seems reasonable. With this deep 
cold trough near the region we could see mountain snowfall and 
colder temperatures for the Thanksgiving weekend (beyond the current 
seven-day forecast period). O'Hara 


&& 


Aviation... 
VFR conditions will continue through Saturday. Areas of haze will 
still be possible around ktvl overnight. Fog is also possible at 
ktrk mainly from 09z through 14z tonight. O'Hara 


&& 


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


$$ 


Http://weather.Gov/Reno