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fxus65 krev 210309 
afdrev 


Area forecast discussion 
National Weather Service Reno Nevada 
709 PM PST Thursday Nov 20 2008 


Update... 
updated winds all zones tonight as wind speeds have dropped off 
and gusts have become localized. Lake wind advisories were allowed 
to expire at 7 PM. Ridge gusts around 40 miles per hour around Lake Tahoe and a 
little stronger in Mono County will continue through the evening. 
Skies have cleared for the most part across the region although 
some lower level moisture remains in the far northern zones and a 
few high clouds will move over areas north of i80 overnight. 
Remainder of forecast looks to be on track and no additional 
updates were made. Rc 


&& 


Previous discussion... /issued 228 PM PST Thursday Nov 20 2008/ 


Short term... 
upper trough moving across Oregon late this afternoon will 
continue to pull off quickly to the northeast. Radar indicates a 
few showers across northern California which will continue to decrease in 
coverage through this evening. Winds will continue to gust through 
this evening...especially north of I-80 where areas along the 
Sierra front will gust 35-40 miles per hour. Shortwave ridge will move into 
the Pacific northwest overnight allowing winds to die down and 
skies to clear. Look for a pleasant day on Friday with high 
pressure over western Nevada. Bumped up temperatures around 2-5 
degrees for tomorrow afternoon with westerly flow. 


A shortwave trough is forecast to move into the Pacific northwest 
on Saturday. Track of this shortwave looks to remain well north of 
the area...however GFS and European model (ecmwf) do generate light quantitative precipitation forecast amounts 
across extreme northern California and Nevada. Kept forecast dry for now with 
uncertainty in the amount of precipitation that will be generated this 
far south. Slight chance probability of precipitation may need to be introduced north of 
Susanville if future model runs continue to indicate precipitation. 
Bumped up winds on Saturday across our northern zones with an 
increased gradient across the area as the shortwave passes by to 
the north. Upper ridge will quickly build across the western U.S. On 
Sunday bringing another nice day across the County Warning Area. 


Light surface flow will keep inversions from mixing out on 
Saturday and Sunday. Expect high temperatures to reach the middle to 
upper 50s in western Nevada valleys each day. Mozley 


Long term...Monday through Thursday... 
with the newest model runs forecast confidence has decreased for the 
latter half of the extended period. The medium range models 
continue to be fairly consistent for the early part of the extended 
in showing a strong ridge over the western Continental U.S. And an upper low over the 
eastern Pacific. The GFS and European model (ecmwf) both show this although the Canadian 
continues to be an outlier by placing its ridge farther to the west 
and places it along the entire west CST from Southern California to southeastern 
Alaska. 


The model solutions start to diverge on Tuesday as the GFS keeps its upper 
low nearly stationary near 30n 135w. The Euro however transitions 
its upper low into an open trough and takes it east toward the West 
Coast on Tuesday. On Wednesday the models diverge even further with 
the GFS weakening its low and building a strong ridge along the West 
Coast. The European model (ecmwf) is quite aggressive in bringing its trough to the 
California coast by 00z Thursday. The models are still out of phase 
on Thursday. Both the GFS and Euro forecast a shortwave moving out of 
the Gulf of Alaska. However this feature simply pushes the GFS 
ridge and the euro's upper trough east into the intermountain west. 


With the models so out of phase...confidence in the temperature and 
precipitation forecasts for the latter part of the extended are affected. 
Monday and Tuesday should remain dry with the upper system still so 
far west. The amplified pattern will also help to keep this system 
from moving very much. However by Wednesday the models are hinting 
at a change in pattern. 


With the European model (ecmwf) progging the upper low to move east...while the GFS 
keeps it stationary...will continue to mention only a slight chance 
of precipitation for the western half of the krev County warning forecast area. This will make it 
easier to adjust the probability of precipitation downward if the Euro slows its progression 
of the upper system. Introduced a slight chance of precipitation to the western 
2/3rds of the County warning forecast area for Thursday as both the GFS and Euro show an eastward 
shift in their features. Kept temperatures slightly above normal 
because of the southerly flow and warm air advection expected east of the 
upper low. Cooled temperatures somewhat for Wednesday and Thursday in 
response to the possible approach of the upper trough. O'Hara 


Aviation... 
VFR conditions will continue through Friday. Gusts to 30 kts 
possible through 21/02z. O'Hara 


&& 


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


$$ 


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