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Area forecast discussion 
National Weather Service Sacramento California 
400 PM PST Sat Nov 21 2009 


Discussion... 
mostly clear skies across much of interior northern California. 
Moderate northwesterly winds developed during the day which 
intriguingly enough initially lifted this mornings fog to a low 
stratus cloud...then advected the stratus cloud southward before it 
finally dissipated. Infrared satellite shows a baroclinic Leaf 
associated with a rapidly advancing storm system currently 
approaching the Pacific northwest. The tail end of this system has 
spread increasing clouds toward the northern end of the valley and 
surrounding mountains. With abundant sunshine today...temperatures 
across the forecast are running a few degrees warmer than 24 hours 
ago. 


The reprieve that we are currently seeing will be brief because of 
the encroaching system. This wave is a fair bit quicker than the 
last and most of its energy will remain north towards Oregon. 
However...warm advection processes will allow some light 
precipitation to develop across the region mainly to the north of 
I-80 late tonight and continue into midday Sunday. Not a whole lot 
of moisture with this system and snow levels should remain 
relatively high...so only light snow accumulations are expected over 
higher elevations. While the bulk of the precipitation is expected 
to remain north of Interstate 80...cannot rule out a few stray 
showers south of that line. 


After this system moves through tomorrow...the eastern Pacific Ridge 
will begin to amplify along the West Coast resulting in a warming 
and dry trend for several days. Surface high pressure building into 
the Great Basin will result in locally northeasterly breezes during 
the overnight hours through favored Sierra canyons. Expect 
temperatures on Monday to warm up to near normal levels in the lower 
60s through the valley and highs on Tuesday to be a few degrees 
above normal. Dang 


Extended discussion (wednesday through saturday)... 
ridge still dominates Wednesday. Other than some patchy morning fog 
expect a generally clear sky Wednesday morning. The models are in good 
agreement with a trough impacting the northern cal on Thursday and into Friday... 
but the GFS and ec are off just a bit on the timing with ec being 
more progressive. This is when the models diverge from one another. 
The GFS only develops a weak ridge over the eastern Pacific and northern cal 
while the ec has a more amplified ridge with trough sliding down 
from British Columbia and into the western Great Basin. The HPC solution used a blend 
of the two...but favored more toward the ec. So went with a slight 
chance of rain over the Shasta and Plumas Colorado mountains Sat. Jmc 


&& 


Aviation... 
VFR conditions expected late this afternoon and early evening. This 
will give way to increasing clouds and showers from north to south 
as a system approaches late tonight. Showers are possible over the 
northern Sacramento Valley after 06z...spreading southward through 
Sacramento by around 12z. This will bring areas of MVFR ceilings with 
local IFR visibilities in heavier rain. Br bringing MVFR/LIFR visibilities is 
possible after 12z over the northern San Joaquin Valley and portions 
of the southern Sacramento Valley where cloud cover will be thinner 
overnight. Snow showers will bring local LIFR in the 
mountains...above 5000 feet in the early evening and dropping to 
3000-4000 by Sunday morning. 


&& 


Sto watches/warnings/advisories...none. 


&& 


$$