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


Synopsis...a warm front will approach the Oregon coast this 
afternoon then push inland this evening. A cold front will quickly 
follow 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...latest model runs continue to exhibit differences in 
track of the surface low coming in tonight. Upper features appear 
pretty well agreed on...with a strong shortwave moving across the 
forecast area tonight...digging to the east-southeast. Given the tract of the 
upper vorticity maximum and the negative tilt of the upper trough...continue 
to prefer a more southerly track of the surface low...as such prefer 
the 00z run of the European model (ecmwf) which takes a surface low east roughly across 
kkls at 12z sun. Timing of the cold front in all models indicates 
frontal passage on the coast not until sometime tonight. Given the 
continued uncertainies in the models...for now will leave headline 
as a high wind watch for the north and central Oregon coast...but limit 
it to tonight period. Winds inland look gusty with and behind the 
front as there are strong pressure rises behind the front. At this 
time though...best guess is for winds to be below warning 
criteria...although Willamette Valley may approach advisory levels 
late tonight. 


Showers continue over most of the forecast area early this morning 
as a westerly flow aloft follows the upper trough. With upper 
ridging later today...and low level flow backing more to the 
S...should see showers drop off today. Overnight snowfall amounts in 
the Cascades since last evening have ranged from roughly 4 to 9 
inches. For now will hang onto the Snow Advisory for the north Oregon 
and S Washington Cascades today...although will likely see a significant 
dropoff in snowfall later this morning. Will upgrade the watch 
tonight to a warning for the Cascades as moisture...strength of the 
front and the Post frontal flow all favor significant snowfall later 
tonight and sun. 


Will back off on probability of precipitation for Sun night and Monday as current model runs 
indicate best chances for precipitation will shift north into Washington with 
best warm front overrunning...and the upper ridge holds cold front 
at Bay until Monday night. 


Long term...no changes. Previous discussion follows... 
weak high pressure builds over the forecast area Monday night. Models show 
a weak system approach the coast early Tuesday...but it tracks further 
north and lightly brushes the far northwest corner of the County Warning Area. This 
ridge is more persistent than previous model runs suggested. It 
manages to delay the arrival of a second system through Thursday. By middle 
next week...models disagree on the solution for the weekend. GFS 
model runs are inconsistent...the 06z run held back on precipitation 
through Thursday night but the current run shows rain extending to the 
Cascades Thursday night. So far...models suggest a fairly nice weekend 
as another upper high pressure temporarily sets up over the Pacific northwest. 
Lramirez 


&& 


Aviation...little change in overall conditions this morning. 
Predominately VFR with scattered showers...which may bring very 
brief MVFR ceilings. Conditions remain VFR through today...though will 
see increasing MVFR along the coast after 20z as warm front swings 
across the region. Cold front tonight will bring increasing MVFR 
after 04z...and increasing southerly winds. 


Kpdx and approaches...VFR conditions through 05z...then increasing 
MVFR ceilings as cold front approaches. Watch for potential of low level 
wind shear between 00z and 06z tonight as will see increasing south 
winds aloft...blowing over the low level easterly flow coming from 
gorge. Rockey. 
&& 


Marine...not much change. Conditions will deteriorate later today 
as warm front lifts across the region. This will bring gale force 
south winds. However...strong winds arrive tonight as rather strong 
low pressure passes across the north Oregon coastal waters. Will hoist 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 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 columbar bar conditions 
through sun. 
Snow Advisory for the South Washington and north Oregon 
Cascades through 4 PM. 
Winter Storm Warning for the S Washington and north and central Oregon 
Cascades tonight and Sunday. 
High wind watch for the northern and central Oregon coast 
tonight. 
&& 


$$ 


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.