038 
fxus66 keka 212203 
afdeka 


Area forecast discussion...updated 
National Weather Service Eureka California 
203 PM PST Sat Nov 21 2009 


Synopsis...a storm system will bring more rain and higher elevation 
snow to northwest California tonight into Sunday. Warmer and dry 
weather is expected for early next week. Another chance of rain is 
expected for late next week. 


&& 


Discussion...skies cleared rapidly early today across northwest 
California...as a stable air mass moved in behind the departing 
cold front. Visible Sat images show a cloud shield moving toward the 
coast...currently beginning to filter over the Redwood coast. This 
will bring addition rain to most of the County Warning Area...with snow at the 
higher elevations. Currently expect snow level to be near 5000 
feet...although some cold air pockets in the Trinity valleys may allow 
a little snow to mix down in certain locations. The likely spots are 
sheltered valleys in eastern Humboldt and western Trinity counties. 
Rain will begin later this afternoon/evening...perhaps as early as 
around 00z...accompanied by the aforementioned snowfall. The event 
will continue through late morning Sunday. Things will taper off 
fairly quickly Sunday afternoon as upper ridging builds into the 
eastern Pacific. 


The upper ridge will move east rapidly Sunday night per GFS 
forecast. The five wave pattern shows a very low amplitude ridge 
over the West Coast with progressive flow over the Pacific. Under 
this scenario the ridge will weaken as a short wave trough swings 
across Vancouver Island on Monday. This may bring some increased 
cloudiness to the far northern County Warning Area but little chance of rain. Upper 
ridging will then return for Tuesday and Wednesday. This will 
provide a couple days of warmer and dryer weather with 500 mb 
heights rising to near 580. Another trough and associated frontal 
band will approach the Pacific northwest coast early Thursday. The European model (ecmwf) is 
slightly faster than GFS and Canadian...and develops a deeper trough 
as it makes landfall early Friday. This time period is when model 
differences start to become significant. For the sake of consistency 
have maintained chance probability of precipitation across the area for Thursday and 
Friday...and indicated an improving trend for Saturday. The air mass 
appears warm enough to support snow levels near 7000 feet...so that 
winter driving conditions are not expected for Holiday travel. CMC 


&& 


Marine...southerly winds will increase this evening ahead of an 
approaching cold front. The front will push east through the waters 
late tonight and Sunday morning...with winds switching to 
northwesterly. Along with a persistent westerly swell...hazardous 
conditions for small craft will continue through tomorrow night. A 
longer period northwest swell will affect the waters by middle 
week...although winds are expected to be relatively light next week. 
Henry 
&& 


Aviation...a cold front will push east through the north coast 
region late tonight and Sunday morning. While not quite as wet as 
the last system...MVFR with areas of IFR conditions are expected 
with prevailing rain showers...mainly starting by the way 03 and 06z along 
the coast...and 05 and 08z inland toward kuki. Behind the 
front...MVFR ceilings are expected to prevail through the day Sunday. 
Henry 


&& 


Northwest California coastal waters... 


Small Craft Advisory until 9 PM PST Sunday for pzz450-455. 


Small Craft Advisory until 4 am PST Monday for pzz470-475. 
&& 


$$ 


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