485 
fxus65 krev 212259 
afdrev 


Area forecast discussion 
National Weather Service Reno Nevada 
259 PM PST Sat Nov 21 2009 


Short term... 
next system to move in tonight is just off the coast with cloud 
shield onto northwest California. System is potent and small...but will deal just 
a glancing blow to the area as it is expected to move into or/WA. 
Decent amount of isentropic lift north of Susanville/Gerlach after 
06z so have increased probability of precipitation to 50/60 percent across these areas. 
Amounts will be light...and precipitation almost all in the form of snow 
despite warming temperatures aloft. Forecast soundings all show near 
isothermal temperature profile through 15z. Cold front with system just 
glances the area Sun morning...so have kept the higher probability of precipitation for 
another 6 hours through mid-morning. By then...moisture and forcing 
with system will have raced eastward. 


700 mb winds also increase near the Oregon border to near 60 kts 
by 12z. However...thermodynamic profile is not favorable for 
mixing these to surface or for mountain waves. As profile improves by 
18z...winds drop off to near 35-40 kts across many areas north of 
Highway 50. Expect a breezy day tomorrow most areas with some gusts up 
to 35-40 miles per hour...but nothing like Friday. Hoisted lake wind 
advisories for Tahoe/pyramid which should be a bit choppy with the 
winds and waves as high as 3 feet. 


Behind system...ridge builds in for Mon/Tue. Ridge is fairly flat 
so it will be dirty with middle/high clouds moving through the north 
at times. Temperatures will be fairly flat through the period in valleys 
with good mixing tomorrw becoming poor by Monday with light NE surface 
winds and warming temperatures aloft. Mountains will see better mixing and 
gradually warming temperatures through period to a few degrees above 
normal. Wallmann 


Long term...Wednesday through Saturday... 


Ridge intact for midweek in quite amplified flow across North 
America. By Thursday the ridge begins to shift east across the 
eastern Great Basin and northern rockies allowing shortwave energy 
to move toward the coast. 


For late in the week model solutions differ. The latest ec brings a 
stronger and colder shortwave to the Sierra and western Nevada 
Thursday night while the GFS and GFS ensemble members have a slower 
solution with a shallower shortwave. The ec would point to showers 
from Tahoe and I-80 north Thursday night into Friday with another 
inside slider type impulse reinforcing the colder air for Saturday. 
The latest GFS and ensembles just generate a glancing blow to far 
northeast California and northwest Nevada Friday with dry and mild 
conditions for Saturday. However the 06z GFS run also indicated an 
inside slider for Saturday night/Sunday much like the latest ec...so 
will have to monitor future models runs for this potential. 


Continued with a chance of rain/snow across northern areas for 
Thanksgiving night through Friday night with model uncertainty. 
Forecast for the weekend after Thanksgiving is even more uncertain 
as mentioned above but will leave that period dry for now. 


Temperatures will be near normal in valley locations with overnight 
inversions...while ridges will warm more under ridge. Also 
anticipate breezy to windy conditions for later in the week. Jah 


&& 


Aviation... 


A shortwave moving into northern California and the Pacific northwest will 
spread clouds and rain/snow showers across the Sierra from Tahoe 
north after midnight through Sunday afternoon. The increase in 
moisture will bring MVFR ceilings to the Sierra with mountain 
obscurement. 


Winds will increase after 06z tonight with ridge winds 50-60kts from 
Tahoe North. Valley locations from Reno north will see gusts to 
30kts after 18z Sunday. Jah 


&& 


Rev watches/warnings/advisories... 
Nevada...Lake Wind Advisory from 10 am to 7 PM PST Sunday for nvz004. 


Lake Wind Advisory from 7 am to 7 PM PST Sunday for nvz002. 


California...Lake Wind Advisory from 7 am to 7 PM PST Sunday for caz072. 


&& 


$$ 


Http://weather.Gov/Reno