Area forecast discussion National Weather Service Portland or 240 PM PDT Friday may 24 2013 Synopsis...an upper low over eastern Washington Friday afternoon will weaken this weekend as it lifts NE into Alberta. A few disturbances will continue to rotate around the low...keeping a threat of showers in through the weekend with temperatures warming a bit closer to normal. An active pattern will continue next week as the flow turns westerly...and a series of weak disturbances come in off the Pacific. && Short term...radar and surface observations have shown showers today largely confined to the mountains today. The upper low has begun to shift east...towards eastern Washington...and is expect to continue NE tonight and Sat. There are still some shortwaves expected to rotate around the low...and drop down the backside of the low this weekend...keeping some threat for showers in. The main shortwave appears to one digging S off the coast Sat night and sun. With the best dynamics digging S...will show the highest probability of precipitation across the southern part of the forecast area Sat night and sun. Models all suggesting some break between systems late Sun night and early Monday. After weak ridging aloft then...the first system in the developing westerly flow off the Pacific approaches Monday. This system too appears likely to send its main energy across the S part of the forecast area. With fairly deep moisture...will bump probability of precipitation up to categorical for latitude Monday in the S...tapering to chance probability of precipitation in the far NE corner. Long term...models start out in good agreement during the extended period Monday night and Tuesday...with a trough pushing inland over the West Coast. Most of the energy appears headed S of the forecast area towards California. As the northern stream appears to remain an open wave...will boost probability of precipitation into likely category. Models diverge some later in the week...but keep a common theme of shortwaves pushing in in a westerly flow aloft. Will keep probability of precipitation relatively high for a system on Wednesday...but then will drop probability of precipitation off later in the week as upper heights rise. && Aviation...weak surface low lingering offshore will be slow to move out of the area this evening. This has kept the region in a moist air mass with weak flow aloft. Therefore showers and local IFR/low MVFR ceilings have remained at the coast...while inland VFR with areas of MVFR will continue through late afternoon. Showers begin to diminish after 00z as the surface flow becomes more southwesterly...while a dry layer pushes into the mid-levels. This dry layer will help trap moisture in the lower levels...for slowly lowering ceilings overnight. Another system will usher rain and low ceilings into the area beginning late tomorrow morning. Kpdx and approaches...expect MVFR in showers to prevail through around 00z...with periods of VFR between showers. VFR should prevail after 00z as shower coverage rapidly decreases. After 06z ceilings will slowly lower back to MVFR...with light drizzle possible overnight. Breezy surface winds will diminish by 03z. && Marine...few updates needed. Seas will remain around 7-8 feet through this evening...before relaxing to near 6 feet tonight. Seas will continue to ease Saturday and remain less than 6 feet through Sunday. Another weak system pushes into the waters early on Saturday...providing breezy winds by Saturday afternoon but winds are expected to remain below 20 knots. A more organized system is expected on Monday which could produce a brief coastal jet for gusts 30 to 35 knots...but this depends on the track. There is still some possibility this system could focus more on southern Oregon and northern California than our waters. Morning ebbs remain very strong due to the full moon...so expect rough Columbia River bar conditions the next couple mornings. Burgess/weagle && Pqr watches/warnings/advisories... or...none. Washington...none. Pz...Small Craft Advisory for rough Columbia River bar from 4 am to 8 am PDT Saturday. && $$ 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.