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.
