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Area forecast discussion 
National Weather Service Portland or 
220 PM PST Sat Nov 21 2009 




Synopsis...a strong Pacific frontal system is approaching the coast 
this afternoon with a warm front moving inland this afternoon and 
evening...and the associated cold front quickly following tonight as 
a surface low pressure system moves inland near the Washington Oregon border. 
A weak ridge of high pressure will follow Sun afternoon and 
night...before the next frontal system arrives Monday. 
&& 


Short term...models are still showing differences in track of the 
surface low coming in tonight. The general consensus is to bring it 
in just north of the Washington/Oregon border. Models are in better 
agreement on the upper features...with a strong shortwave moving 
across the forecast area tonight...digging to the east-southeast. Timing of the 
cold front in all models indicates frontal passage on the coast 
around midnight tonight. Have upgraded the high wind watch for the 
entire coast to a High Wind Warning. Winds inland look gusty with and 
behind the front as there are strong pressure rises behind the 
front...will issue an advisory for the Willamette Valley..I-5 
corridor and the lower Columbia for tonight and early Sunday morning 
with the afternoon package. 


Doppler radar indicates that showers have significantly diminished 
over the area with only an isolated shower or two over the South 
Washington Cascades and have already cancelled the Snow Advisory for 
the Cascades. Will continue the Winter Storm Warning for the 
Cascades as moisture...strength of the front and the Post frontal 
flow all favor significant snowfall for later tonight and sun. 


A weak upper ridge will build over the forecast area Sunday night and 
Monday following the front. Best chances for precipitation Monday and 
Tuesday will shift north into Washington with warm front overrunning. The upper 
ridge holds cold front at Bay until after Tuesday night. Likens 


Long term...weak high pressure ridge over the forecast area continues to 
push energy north of forecast area middle week. It manages to delay the 
arrival of a second system through Thursday. Model solutions diverge 
toward the end of the week and have little confidence in them. At 
this time will go with climatology until there is some consistency 
between the models.. 


&& 


Aviation...predominately VFR with scattered showers...which may 
bring very brief MVFR ceilings. Conditions remain VFR this 
afternoon...though will see increasing MVFR along the coast as warm 
front swings across the region. Cold front tonight will bring 
increasing MVFR after 04z...and increasing southerly winds some of 
which may be quite strong in some areas. Location of strong winds 
will depend on where the low comes inland. 


Kpdx and approaches...VFR conditions through 05z...then increasing 
MVFR ceilings as cold front approaches. Watch for potential of low level 
wind shear between 06z and 18z tonight and tomorrow morning as will 
see increasing south winds aloft...blowing over the low level 
easterly flow coming from gorge. South to southwest winds may be 
quite strong around 12z as strong gradient develops over North 
Valley as low moves inland. Wind gusts near 50 to 55 miles per hour are 
possible. Wolfe 
&& 


Marine...gale force south winds will strengthen to storm force as 
potent low moves over the coastal waters. Storm Warning for the 
coastal waters for tonight. Winds turn more west to northwest on Sunday and 
begin easing. Seas tonight likely to peak in the 20 to 25 feet 
range...but will drop quickly to the middle teens on sun. 
&& 


Pqr watches/warnings/advisories... 
WA/OR...Gale Warning for coastal waters from Cape Shoalwater to 
Florence for this afternoon. 
Storm Warning for coastal waters from Cape Shoalwater to 
Florence for tonight. 
Small Craft Advisory for rough Columbia River bar conditions 
through sun. 
Winter Storm Warning for the S Washington and north and central Oregon 
Cascades tonight and Sunday. 
High Wind Warning for the southern Washington/northern and 
central Oregon coast tonight. 
Wind Advisory for the Willamette Valley..the lower 
Columbia..and the I-5 corridor for this evening through 
Sunday morning. 
&& 


$$ 


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.