Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 310952
Area Forecast Discussion
National Weather Service Portland OR
252 am PDT Tue May 31 2016
.SYNOPSIS...An upper level ridge will persist over the Pacific
Northwest today, bringing mostly sunny skies and warm temps 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.
Another upper ridge builds over the region at the end of the week.
.SHORT TERM...(Today through Thursday)...A strong upper ridge was
seen in water vapor pictures along the coast Tue morning. An
inverted trough of low pres along the coast had brought a light
offshore flow to the region. Models generally agree this thermally
induced trough to shift inland into the Coast Range today, resulting
in a turn to onshore flow along the coast in the afternooon. With
inland h8 temps expected on the order of 16 to 18 deg c, expect to
see high temps in the range of 85 to 90 today, while coastal areas
are likely to see diurnal heating cutoff in time to hold temps in
A couple of shortwaves, the first seen on satellite near 140w, will
flatten the ridge tue night and wed night. As a result the surface
trough is expected to push e of the Cascades, turning the low level
flow onshore. Time height cross sections suggest a decent shot of
low and mid level moisture pushing inland by wed night esp in the
north, which coupled with the second shortwave will bring a chance
for some precipitation mainly to the coast and north wed night into
thu. With the return to marine air, temps will progressively cool
some Wed and Thu.
.LONG TERM...(Thursday night through Sunday)...No changes.
Previous discussion follows. 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. By later Sunday, the upper ridge migrates
eastward as an upper low over northern California begins to lift
north towards the region. With additional moisture pushed into the
region and decent instability, have expanded the chance of
thunderstorms, though still primarily restricted to the Cascades and
.AVIATION...Expect VFR conditions to continue through early Wed.
Diurnally driven northwesterly winds will become breezy again
this afternoon and evening.
PDX AND APPROACHES...VFR conditions expected through early Wed.
Light east wind develops later this morning with local gusts to
25 kt over eastern approaches 15z through about 22z Tue. Winds
ease then shift to the northwest in the early evening. /mh
.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 is leading to
gusty winds along Oregon marine waters. However models have backed
off on the strength of the wind so have adjusted the small craft
advisory for winds. Wind over the outer waters are expected to
increase later this morning and expand to the near shore waters in
the afternoon. Overall expected wind to decrease later this
evening and overnight as high pressure off the coast weakens and
the thermal low shifts east of the Oregon Cascades.
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
Small Craft Advisory for winds until 5 AM PDT early this
morning 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.