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fxus66 kpqr 050439 
afdpqr 


Area forecast discussion 
National Weather Service Portland or 
832 PM PST Wednesday Nov 4 2009 


Synopsis...dry offshore flow will transition to a damp and windy 
pattern beginning tonight and Thursday as the first in a series of 
Pacific frontal systems approach the area. Strong winds are possible 
along the coast Thursday and Thursday evening. Snow levels will fall 
with significant accumulations expected in the Cascades late 
Thursday night through Saturday. In addition large west swell will 
arrive Friday and Saturday bringing powerful waves to the coast. 


&& 


Short term...offshore flow will gradually diminish this evening and 
overnight as the surface high over the Columbia River basin weakens. 
The pressure gradient between The Dalles and Troutdale is still at 
6.6 mb so east winds through the west end of the Columbia River 
gorge should continue for a while yet. The winds along the coast have 
already shifted to the south as a Pacific front approaches from the 
west. The low associated with this front is very powerful with a 
central pressure below 950 mb. Luckily...it will remain in the Gulf 
of Alaska. That being said...the associated front will still pack 
quite a punch as it moves through Thursday afternoon and evening. The 
rain will develop Thursday morning along the coast and spread inland 
through the day. Precipitation intensity will become moderate to 
heavy at times by Thursday evening as the main cold front makes 
landfall. Winds along the coast may reach low end warning criteria. 
The greatest threat of damaging winds will be confined to the 
beaches and headlands between 4 PM and 10 PM Thursday. It will also 
be quite gusty across the rest of the forecast area Thursday evening 
as this cold front moves by. Will maintain the high wind watch 
along the coast for now since confidence is not that great for what 
would be a 3rd period event. 


Snow levels will fall to 6000 feet Thursday night with around a foot 
of new snow possible above that elevation. Snow levels will fall to 
3000 to 4000 feet on Friday with cool unstable onshore flow and Good 
Ridge level winds. Another frontal system will swing inland on 
Saturday increasing precipitation rates once again. 


Long term...no changes. Previous discussion follows...showers will 
continue Saturday night then taper off on Sunday as a transient 
ridge moves through bringing a brief break between systems. The next 
frontal system will reach the coast around Monday then move inland 
Monday night. A cool upper level trough will bring showery weather 
with snow levels in the 3000 foot range through around Thursday. 
This series of systems next week on top of the mountain snow fall 
anticipated Thursday night through Sat night will provide a good start 
for winter snowpack. Ruthford/rain shower 


&& 


Aviation...VFR conditions this evening...except local MVFR ceilings 
along the coast. As rain spreads ahead of an approaching 
front...MVFR ceilings and visibilities will develop along the coast later 
tonight and Thursday...with MVFR ceilings in the interior possible by 
late afternoon. High winds are expected along the coast beginning 
Thursday morning. 


Kpdx and approaches...VFR conditions into Thursday afternoon. May 
see some MVFR ceilings late Thursday afternoon with approaching front. 


&& 


Marine...winds increasing ahead of a strong front will reach gale 
force later this evening and continue through Thursday evening. The 
front is expected to move inland by Thursday evening followed by 
moderating winds. A combination of systems is resulting in a deep 
low and a long fetch developing in the Gulf of Alaska. The resulting 
large swell will begin arriving Thursday night...peaking in the 25 
to 30 feet range Friday night. Swell will diminish over the weekend 
but remain high and winds likely to meet Small Craft Advisory levels 
as the weather remains unsettled. 


&& 


Pqr watches/warnings/advisories... 
WA/OR...Gale Warning from Cape Shoalwater to Florence 
this evening through Thursday evening. 
Small Craft Advisory for winds from Cape Shoalwater 
to Florence in effect through this evening. 
Small Craft Advisory for rough Columbia River bar in 
effect through this evening and again Thursday morning. 
Minor tidal over flow Thursday afternoon southwest Washington 
coast. 
High wind watch for the north and central Oregon coast 
Thursday midday through Thursday 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.