Weather

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Area forecast discussion 
National Weather Service Portland or 
900 am PDT Friday Oct 10 2008 


Synopsis...the upper level low pressure area that brought a cold 
air mass to the forecast area has moved southeast with north to 
northeast flow aloft developing. Isolated showers may linger along 
the Oregon Cascades but clouds will be departing as the day 
progresses. A ridge of high pressure aloft building offshore will 
move inland by Sunday...but is expected to weaken early next 
week...allowing a Pacific cold front to move inland to brush the 
north part of the forecast area. 
&& 


Short term...an upper level low pressure center has now moved to 
southwest Idaho out of the area but isolated showers may still rotate 
around the low into the Cascades for a while today....not much is 
showing up on radar now but there are still some cool top cells on 
the infrared imagery. The air mass is cold as shown by a freezing 
level of 3500 feet at Salem this morning...placing snow level down to 
around 2500 feet. Any light snow showers would be very isolated and 
limited to Oregon Cascades. A positive high pressure area aloft is 
building offshore and already nosing into western Canada which will 
turn flow northeast and as clouds decrease with such a cool air mass 
expect the coolest night of the fall by Sat morning. Morning 
temperatures will be especially cool in the High Mountain valleys 
where a couple inches of new snow fell. Terrestrial radiation will 
be high there tonight with some min temperatures in the 20s. Areas of 
Willamette Valley temperatures will also fall below freezing tonight 
so have issued a frost advisory. Fog will develops later tonight into 
Saturday morning in The Lowlands. It will be a cold start for Sun 
morning as well as the air mass warms a bit but dries out more to 
help night time radiation. Willson 


Long term...no changes. Previous discussion follows... 
the models are varying but looks like the ridge stays strong enough 
to keep most of the precipitation to the north brushing the northwest 
part of the forecast area at times into the extended. 


&& 


Aviation...a mix of VFR and MVFR ceilings across the interior this 
morning...with patchy IFR conditions along the coast. Conditions 
will improve to VFR this afternoon except for some linger showers 
and mountain obscuration over the Cascades and possibly the Coast Range. 
VFR conditions will prevail overnight...with possible IFR fog 
forming late tonight in sheltered interior valleys. 


Kpdx and approaches...MVFR ceilings will continue until midday 
today. VFR conditions will prevail tonight. There is a 30 percent 
chance of IFR conditions reforming after 10z Saturday morning. 
&& 


Marine...winds have fallen below small craft levels across the 
northern waters this morning. Winds will remain near small craft 
levels across the central coast today as the thermal trough 
strengthens to our south. Seas above 10 feet this morning will drop in 
the north by early afternoon and in the south in the early evening. 
Will still have a rough Columbia River bar through this morning. 
&& 


Pqr watches/warnings/advisories... 
or/WA...frost advisory in effect from 6 am to 9 am Saturday for the 
Coast Range of northwest Oregon...the central Coast Range of 
western Oregon...the lower Columbia...greater Portland metropolitan 
area...central Willamette Valley...south Willamette Valley...western 
Columbia River gorge...Willapa Hills...I-5 corridor in Cowlitz 
County...and the Greater Vancouver area... 
Small Craft Advisory for winds Cascade Head to Florence 
through this evening. 
Small Craft Advisory for hazardous seas Cape 
Shoalwater to Cascade Head through this morning. 
Small Craft Advisory for hazardous seas Cascade Head to 
Florence through today. 
Small Craft Advisory for rough Columbia bar through this 
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.