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fxus66 kpqr 212125 
afdpqr 


Area forecast discussion 
National Weather Service Portland or 
224 PM PDT Thursday Aug 21 2008 


Synopsis...a broad low pressure area aloft will continue moving east 
of the region tonight...with any residual showers ending this 
evening. High pressure will build inland over the region Friday with 
dry and warm weather anticipated through most of the weekend. Another 
wet Pacific weather system is expected to affect the area from late 
Sunday through Monday of next week. 
&& 


Short term...satellite imagery shows the large upper level low pressure 
area now centered near the southeast British Columbia/northwest Montana area this afternoon...and 
continuing to move off to the east. Visible satellite and radar show 
decreasing mainly mountain showers...which will end early this 
evening as moist onshore flow and low level instability ends. 


A ridge of high pressure aloft will rebuild along the Pacific northwest coast 
tonight and move inland Friday with weak offshore flow developing by 
Friday morning. This will produce clearing skies and warming temperatures Friday 
with a return to more typical Summer weather. The upper level ridge 
will continue over the area Sat for mostly sunny conditions with 
additional warming inland. Onshore flow along the coast both Friday and 
Sat will maintain cooler temperatures at the beaches. 


For sun models fairly consistent showing another strong upper low 
moving into the Gulf of Alaska...with a moist Pacific front spreading rain 
back into the area by Sun night...and possibly as early as Sun 
afternoon on the coast and Coast Range. Rain shower 


Long term...showers follow the cold front on Monday as the main upper 
trough swings inland. Models then show variations Tuesday through Thursday 
with the possibility of additional low amplitude upper troughs moving 
through the Pacific northwest in fairly fast westerly flow aloft...with the main 
threat of showers likely remaining north of our area. Rain shower 
&& 


Aviation...a few showers continue over the northern Coast Range and 
Cascades this afternoon. These showers will continue to around 
sunset then end as high pressure offshore builds over area. Onshore 
flow will continue this evening then diminish as high pressure 
shifts into eastern Oregon later tonight. Most areas are VFR this 
afternoon with a few local MVFR cloud areas. VFR conditions will 
continue this evening. By morning flow will become light over area. 
Moist low level air mass will allow areas of stratus and patchy fog 
to form over inland valleys and some coastal valleys late tonight. 
This will give areas of IFR conditions. High pressure will build 
offshore Friday afternoon. This will give drier north to northwest 
flow to area. All areas of stratus and fog will clear by midday. 


Kpdx and approaches...VFR conditions in the kpdx area this afternoon 
will continue most of tonight. Areas of stratus and fog will form 
late tonight with a 60 percent threat of IFR conditions at kpdx by 
daybreak Friday. Stratus and fog will clear by late morning with VFR 
conditions Friday afternoon. 
&& 


Marine...high pressure building into waters this afternoon will 
extends inland tonight. High pressure will build offshore Friday 
afternoon with thermal trough developing over northern California. 
Winds will remain below small craft levels tonight and Friday 
though winds may get close to small craft Friday afternoon along 
the central coast. Seas around 10 feet this afternoon and evening 
will drop below 10 feet tonight. 
&& 


Pqr watches/warnings/advisories... 
or/WA...Small Craft Advisory for hazardous seas Cape 
Shoalwater to Florence through 11 tonight. 
Small Craft Advisory for rough Columbia River bar through 
this evening. 
&& 


Preliminary point probability of precipitation (probability of measurable precipitation) 
AST 100-13 pdx 1000-1 sle 1000-1 eug 1000-1 


$$ 


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.