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Area forecast discussion 
National Weather Service Portland or 
838 am PST Monday Nov 23 2009 


Synopsis...a weak warm front off the coast will shift northeast 
today...then a weak cold front will sag southeast into northwest Oregon tonight. 
The front will stall late tonight...then lift NE as a warm front on 
Tuesday. The next frontal system is not expected to move in until late 
Thursday. 


&& 


Short term...the main threat for rain though today should be over 
the northwest part of the forecast area...where isentropic lift is best 
ahead of the warm front offshore. 


Models indicate a cold front sagging down into the region late today 
and tonight. Will need to include probability of precipitation most areas by tonight and 
early Tuesday with baroclinic zone over the area...but with weak dynamics 
probability of precipitation will be limited to chance to likely category. Front lifts back 
to the north late Tuesday and Tuesday night with the upper ridge 
rebounding...resulting in diminishing probability of precipitation by Tuesday night...and a dry 
day Wednesday. Wolfe 


Long term...no changes. Previous discussion follows... 
models in some agreement on bringing a frontal system and its 
associated upper level trough through the region Thursday/Thursday night for a 
return to wet weather. After this system moves through...the weak 
high pressure ridge reasserts itself over the forecast area...keeping 
most energy north of forecast area. Fog may be more of a problem in 
the extended. 


&& 


Aviation...much more tranquil today. Primarily VFR conditions 
across the region. A warm front approaching from the west will 
spread areas of MVFR with occasional rain along the coast around 20z. 
May see some sprinkles inland as the warm front passes through...but 
remaining generally dry with VFR through 02z. 


Kpdx and approaches...no adverse weather impacts expected. VFR 
conditions to remain through 06z tonight. 


&& 


Marine...low pressure is moving into Vancouver Island this 
morning...pushing a warm front into the Washington/or coastal waters. 
Associated cold front extends SW from low and will not directly move 
through waters until midweek. Winds just behind warm front may 
approach gale in a few gusts...but for now Small Craft Advisory for winds/seas appear 
sufficient. Seas will remain in the 10-13 feet range through today... 
but may fall below 10 feet for a time tonight and Tuesday. Generally 
tranquil weather then expected into Wednesday...then the cold front will 
finally slide across the coastal waters Wednesday night/Thu. Some models 
show the possibility of a strong low developing along this front off 
the Oregon coast Wednesday night or early Thursday...will need to monitor this 
for potential gales during that time period. Weagle 


&& 


Pqr watches/warnings/advisories... 
WA/OR...Small Craft Advisory for hazardous seas Cape Shoalwater to 
Florence out 0-60 nm through Tuesday. 
Small Craft Advisory for winds Cape Shoalwater to Cascade 
Head out 0-60 nm and Cascade Head to Florence out 20-60 
nm today. 
Small Craft Advisory for rough Columbia River bar through 
this evening. 
&& 




$$ 


More weather information online at... 
http://weather.Gov/Portland 




This discussion is for northwest Oregon and southwest Washington from 
the Cascade crest to 60 nautical miles offshore. The area is commonly 
referred to as the forecast area.