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


Discussion... 
clearing skies have developed across much of the forecast area in 
the wake of Friday/S system. Much of the valley has cleared out 
while some low cloudiness and a few light showers linger over the 
west slopes of the northern Sierra Nevada. Much of this remaining 
cloudiness is expected to erode by sunrise as a little stronger 
subsidence develops in the wake of the system. In the valley...wet 
ground and clear skies have allowed patches of dense fog to develop 
and these will likely last through middle-morning before northerly flow 
and better mixing develop. 


Water vapor satellite imagery shows another fast moving wave moving 
into far northern California early this morning...but any upward 
vertical motion associated with this feature is staying well to the 
north and east. A more significant wave is evident crossing 150w and 
will slide southeastward brushing far northern California late 
tonight and Sunday. Much of the energy with this next wave will be 
focused further to the north into Oregon as ridging builds over the 
eastern Pacific. 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. Precipitation 
amounts are expected to be rather light...generally less than a 
quarter inch across the higher terrain and perhaps a few hundredths 
of an inch over portions of the northern Sacramento Valley. 


More substantial ridging is forecast to develop over the eastern 
Pacific and northern California early next week and continue much of 
the week. Much milder temperatures are forecast to return to the 
foothills and mountains...while milder valley temperatures will 
depend on how strong offshore flow gets during the week and whether 
it provides enough mixing to realize some of this warming at the 
lower elevations. All medium range models indicate another system 
weakening as it moves into the ridge later Thanksgiving or Friday 
with the European model (ecmwf) faster on the timing of either the GFS or Gem. 


&& 


Aviation... 
upper trough moves into Great Basin this morning as weak high builds into norcal 
today. Warm front and associated upper trough move into norcal tonight into sun. For 
interior norcal areas IFR/LIFR conds in fog/St until around 18z otherwise VFR 
conds through 06z sun. For Central Valley after 06z sun...areas of MVFR/IFR 
conds mainly north of I-80 in -ra/br. For fthls/mountains after 06z sun...widespread 
IFR and local LIFR conds obscrg terrain developing from north-S overnight Sat into Sun 
morning. Snow levels generally 045-055 mean sea level. Areas westerly surface wind gusts to 30 kts or 
gtr over hyr mountain terrain after 06z sun. 


&& 


Sto watches/warnings/advisories...none. 


&& 


$$