Area forecast discussion
National Weather Service Portland or
202 am PDT Wednesday Jun 19 2013
Synopsis...upper level low that has been lingering off the
Washington and Oregon coast for the past several days is now moving
inland. This will bring cool and showery weather today with a low
threat for thunderstorms over the Cascades. Showers will gradually
taper off Thursday and Friday as the upper low lingers over eastern
Washington. The weekend warmup is looking less likely with recent
model runs...in fact some models are bringing in a Pacific frontal
system for more rain possibly on Sunday.
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Short term...scattered showers continue to rotate around the upper
low now nearing the coast early this morning. The low is forecast to
shift over the forecast area today for continued showers in the
unstable air mass. Model soundings begin to stabilize the upper
levels in the afternoon. This should limit vertical growth of showers
so charge separation can not occur. However stabilization over the
Cascades should be a little later and combined with the high terrain
may provide the additional lift needed to produce thunderstorms. As
a whole cooler than normal temperatures with showers today.
By Thursday the trend has been for slower movement of the
system...with it lingering somewhere over the middle-Columbia Basin
Thursday. With this proximity there will be the continued threat of
wraparound moisture and showers. By Friday the low is further east
lowering the threat for showers and high temperatures approaching
seasonal normals.
Long term...Friday night through Monday...given the last couple of
model runs we are starting to lose confidence in our weekend ridging
and warmup. The upper low festering over the middle-Columbia Basin now
appears to linger into Friday...not really allowing the upper ridge
to build in full force before the next Pacific frontal system
approaches for the weekend. There are a couple factors to consider
here. There is a historically strong upper level ridge over Alaska...
with our upper low stuck below it in a Rex block pattern. The
tendency will be for the Pacific jet to try to undercut the alaskan
ridge this weekend and this is what the models are beginning to show.
Additionally the Madden-Julian oscillation seems to be entering its
most active phase since February...which is impressive for June. All
this points to a wet week next week...so we significantly trended
probability of precipitation upward and cooled off temperatures beginning Sunday. Weagle
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Aviation...mostly VFR this am...but do have areas of MVFR and
localized IFR ceilings on central Oregon coast. These conditions will
spread north along the coast with mix of MVFR and brief VFR this am.
Further inland...VFR. But do have areas of MVFR ceilings from Cowlitz
valley S to kpdx and kttd...and along S Washington/north or foothills. These
lower clouds will back build from the Cascades and cover a large
part of the interior...mainly between 10z and 19z. Ceilings should
break up after 19z...with mix of VFR and localized MVFR with the
scattered showers.
Kpdx and approaches...MVFR ceilings have formed across the area as
rain cooled air from east arrived. Worst conditions to north and east of
kpdx at moment...as areas to S and west are VFR. MVFR ceilings will
spread across rest of Ops area through 14z...and persist through
at least 18z.
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Marine...little change as a broad area of low pressure offshore will
continue to slowly track toward the coast through Wednesday. Winds
generally 10 to 15 knots. Seas will remain at 3 to 5 feet through Sat.
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Pqr watches/warnings/advisories...
or...none.
Washington...none.
Pz...none.
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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.
