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fxus66 kpqr 211546 
afdpqr 


Area forecast discussion 
National Weather Service Portland or 
845 am PDT Thursday Aug 21 2008 


Synopsis...a broad low pressure area aloft over the Pacific 
northwest will slowly shift to the east today...with showers 
decreasing over the forecast area. 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 may affect 
the area Sunday night into early next week. 
&& 


Short term...satellite imagery shows a large upper level low pressure 
area shifting slowly east across southern British Columbia this morning...with GFS 
showing an elongated center extending from southeast British Columbia into northwest Montana by late 
afternoon. The associated trough over the Pacific northwest combined with moist 
onshore flow will continue to produce showers over the forecast area 
this morning...especially mountain areas. The showers will decrease 
in coverage and intensity as the trough moves inland and onshore flow 
weakens this afternoon into early this evening. 


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 
continues 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. Rain shower 


Long term...no changes. Previous discussion follows...models show 
the upper ridge shifting east on sun as the next Pacific trough moves into 
the Gulf of Alaska. Model consistent showing the associated front 
beginning to move into the northern coastal waters on sun...then some 
timing differences moving through the region Sun night into Monday. 
Northern areas should have the best chance of rain where 500mb 
heights fall the most. Models then show increasing variation Tuesday and 
Wednesday with the possibility of additional upper troughs moving through 
the Pacific northwest in fairly fast westerly flow aloft...with the best threat 
of showers remaining north of our area. Rain shower 
&& 


Aviation...upper trough over northern Washington this morning will 
move east this afternoon. Showers mainly north associated with 
trough will decrease this afternoon but some showers will linger 
until early evening inland north. High pressure building into 
northern coast this afternoon will continue west onshore flow over 
area. High pressure builds inland tonight. Onshore flow decreases 
with light flow late tonight. There are areas of MVFR this morning 
with local IFR along the central coast. VFR will return to all areas 
this afternoon with local MVFR near any showers. VFR conditions will 
continue this evening with clouds clearing over the inland areas 
after midnight. 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. 


Kpdx and approaches...areas of MVFR will continue this morning in 
the kpdx area with all areas VFR by early afternoon. VFR conditions 
continue tonight. Areas of IFR are possible by sunrise Friday with 
stratus and patchy fog. 
&& 


Marine...high pressure builds into waters this afternoon then 
extends inland tonight. Winds will remain below small craft levels 
through tonight. Seas 10 to 12 feet today will drop below 10 feet 
tonight. 
&& 


Pqr watches/warnings/advisories... 
or/WA...Small Craft Advisory for hazardous seas Cape Shoalwater 
to Florence through 2 am Friday morning. 
Small Craft Advisory for rough Columbia River bar through 
this evening. 
&& 


Preliminary point probability of precipitation (probability of measurable precipitation) 
AST 6100- pdx 51000 sle 51000 eug 41000 


$$ 


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.