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


Discussion... 
dry and mild weather expected across interior northern California 
the next few days as high pressure builds along the West Coast. The 
primary concern in the short term is fog. A narrow finger of fog 
developed overnight in the typical Mountain Valley basins and along 
the wind-sheltered eastern portions of the valley...primarily 
Roseville southward. This fog is expected to dissipate by late this 
morning...setting the stage for a pleasant fall afternoon. Will 
update forecast to tweak wording as fog continues to dissipate. 
Temperatures should warm a few degrees over yesterday...highs should 
range in the 60s through the valley and foothills and in the 50s 
over higher elevations. Temperatures should warm another degree 
tomorrow and Wednesday as high pressure continues to build into the 
area. Surface high pressure will remain in the Great Basin the next 
few days...resulting in gusty overnight conditions down west facing 
Sierra canyons. Dang 


Previous discussion... 
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... 
surface high pressure over the Great Basin with the thermal trough 
over California bringing north to northeast winds. Areas of fog 
bringing LIFR conditions along the east side of the valley from kmhr 
through to east of kmer and on south until 18z. Patchy fog also in 
the mountain valleys bringing local LIFR/IFR conditions until 18z. 
Breezy North-East winds near Sierra Nevada crest and through canyons along west 
slopes. VFR conditions expected everywhere after 18z and then fog 
reforming in the mountain valleys after 08z until 17z Tuesday. 


&& 


Sto watches/warnings/advisories...none. 


&& 


$$