779 
fxus66 ksto 231155 
afdsto 


Area forecast discussion 
National Weather Service Sacramento California 
330 am PST Monday Nov 23 2009 


Discussion... 
beautiful dry and mild Fall weather expected across the interior of 
northern California much of this week as the persistent West Coast 
ridge remains in place. The ridge is expected to steer weather 
systems to the north of the region through the middle of the week 
with subsidence and dry northerly flow dominant through Wednesday. 
West facing canyons and higher elevations of the northern Sierra 
Nevada will see locally breezy east winds late at night and in the 
mornings the next several days as surface high pressure is centered 
over the Great Basin. Pattern is not conducive for fog...though will 
likely see some areas of late night and morning fog in the mountain 
valleys and possibly along the east side of the Central Valley which 
will be more sheltered from the north winds. 


Next system advertised by the models to bring a chance of 
precipitation as early as Thanksgiving night across the northern and 
coastal mountains and perhaps the northern Sacramento Valley...but 
the system like several previous is advertised to split as it moves 
into the ridge over the west which will weaken it and possibly slow 
its eastward progression. 


Extended discussion (friday through monday)... 
short wave moves through the region late Thursday night and into the 
Great Basin Friday. The European model (ecmwf) is slower and farther north than the 
06z GFS. 90kt jet over the region Ushers in colder air on Friday and 
we cooled high temperatures in the valleys into the 50s...with 
isolated showers mainly north of Sacramento. In the mountains 700mb 
temperatures of -6c yield an initial estimate of 4000-5000 foot snow 
levels. Ridge amplifies strongly behind this system Saturday and 
Sunday. Dry weather should result with near normal temperatures. GFS 
has a 1037mb surface high over Idaho 12z Monday...possibly leading 
to gusty east winds in the mountains and foothills. This would be a 
favorable pattern for a barrier jet to form along the west side of 
the valley. Ensemble spread becomes huge by Monday as the models 
struggle with energy ejecting out of the Bering Sea low and a modest 
mjo (madden Julian oscillation) disturbance in the western Pacific. 
Our Monday forecast is dry for now but we will keep a watchful eye 
out for any sign of undercutting of the westerlies. Snow grains 


&& 


Aviation... 
strong surface high pressure over the Great Basin and northern 
California. North flow aloft. Area of IFR ceilings br east of kmhr-ksck with 
only limited MVFR 3-5sm patchy br to affect the terminal sites 
themselves 13z-17z. Limited LIFR in High Mountain valleys until 17z. 
Breezy east winds near Sierra Nevada crest and through canyons along west 
slopes. VFR all areas bynd 18z. Snow grains 


&& 


Sto watches/warnings/advisories...none. 


&& 


$$