Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 311606

Area Forecast Discussion
National Weather Service Portland OR
906 AM PDT Tue May 31 2016

.SYNOPSIS...An upper level ridge will persist over the Pacific
Northwest today, bringing mostly sunny skies and warm temperatures
to southwest Washington and northwest Oregon. Onshore flow will
start to develop by Wednesday as a weak disturbance approaches the
region, with the remains of a surface front clipping Southwest
Washington by early Thursday. Another upper ridge builds over the
region at the end of the week.


.SHORT TERM...(Today through Thursday)...A look at the synoptic
pattern via water vapor imagery depicts a strong upper level ridge
centered near the coast, while a low pressure system upstream near
140W will continue to lift north into the Gulf of Alaska today. The
associated front is aligned to the south, currently located near
135W, well offshore and to the north of the region.

Closer to home, light offshore flow continues near the surface with a
thermal trough aligned along the coast. Short term models continue to
agree that this will shift into the Coast Range today, which will
bring onshore flow to the coast later this afternoon. Model 850 mb
temperatures have trended just a bit cooler over the last 24 hours,
but will these temperatures still on the order of 16 degrees C, the
forecast highs of 85 to 90 for the interior locations looks to be on
track. Meanwhile, coastal sites will likely see the onshore flow
develop before maximum heating can be achieved and will see
temperatures generally constrained in the lower 70s.

A pair of weak shortwaves in the flow will flatten the ridge tonight
and Wednesday night, resulting the the surface trough pushing east of
the Cascades, which will bring a return of onshore low level flow
across the area. This marine air will bring increasing clouds to the
region as well as bring cooler, albeit still warmer than seasonable,
temperatures. Latest forecast models are somewhat pessimistic with
regard to much in the way of mid-level moisture tonight, but the
impulse late Wednesday night may have enough mid and low level
moisture to generate some light precipitation Wednesday night through
Thursday - especially across the northern portions of the area and
along the coast - though any accumulation with be rather
minimal.                                 /Cullen

.LONG TERM...(Thursday night through Sunday)...Good agreement
continues in the forecast models with respect to the end of the week
with a strong ridge developing over the southwestern U.S. Thursday
night and amplifying into the weekend. With 850 mb temperatures over
the area climbing to 18-22 degrees C, another stretch of warmth on
Friday and Saturday is expected. Given the latest trends, have
increased temperatures across the interior on Saturday and Sunday to
reflect the lower 90s Saturday and perhaps around 90 on Sunday. Of
note, a handful of record highs on Saturday are in the 89 to 91
degree range, so it is possible that new daily records could be set
at a few area stations.                  /Cullen


.AVIATION...Expect VFR conditions to continue through early Wed.
Diurnally driven northwesterly winds will become breezy again
this afternoon and evening. stratus may develop along the coast
tonight with a 50 percent chance of IFR cigs developing along the
central coast of oregon aft 09z and spreading northward to the
south washington coast by 14z.

KPDX AND APPROACHES...VFR conditions expected through early Wed.
Light east wind possible this morning later this morning with
local gusts to 20 kt over eastern approaches 15z through about
22z Tue. Winds ease then shift to the northwest in the early
evening. schneider


.MARINE...A high pressure center is located off the Washington
coast while a thermally induced pressure trough over northern
California and southern Oregon. This combination will resulting
increasing winds over the Oregon marine waters. Models continue to
be weaker on the strength of the winds, however believe that low
end craft winds will occur this afternoon and evening. wind
expected to decrease later this evening and overnight as high
pressure off the coast weakens and the thermal low shifts east of
the Oregon Cascades. Schneider

A similar thermal low setup will strengthen marine winds Saturday
through Monday with small craft strength winds likely. In
addition, expect this long duration northerly fetch to increase
seas to the 7 foot range. Given the primarily wind wave
dominated/fresh swell seas, expect relatively short periods could
bring square seas concerns during this period. Otherwise, seas
expected to remain between 3 and 6 feet through the remainder of
this week. /mh


PZ...Small Craft Advisory for winds until 11 PM PDT this evening for
     Waters from Cape Shoalwater WA to Florence OR from 10 to
     60 nm.

     Small Craft Advisory for winds from 2 PM this afternoon to 11
     PM PDT this evening for Coastal Waters from Cape
     Shoalwater WA to Florence OR out 10 nm.



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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. is the U.S. government's official web portal to all federal, state and local government web resources and services.