Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
923 am PDT Sat Aug 29 2015
Synopsis...the usually early and strong low pressure system that was
forecast to affect our area has done pretty much what it was supposed
to...with high wind along the coast and in the higher coastal
mountains with some local power disruptions...windy conditions
inland...and a line of thunderstorms as the front moved through
southwest Washington and northwest Oregon earlier this morning. The
strong surface low was moving north along the Washington coast and
will be well north of our area by middle afternoon. Another cold front
on its heels and partially merged with the bent back occlusion will
move onto the north coast areas this afternoon and move through our
forecast area tonight...with a few thunderstorms possible especially
near the coast. Onshore flow behind the front will keep a fair amount
of showers over the area Sunday. A trough will remain near the coast
through the coming week...keeping things cool and showery at times.
Short term...things have turned out not too far from what was
expected the last few days and as indicated in our afds and
statements. A strong low moved up the coast and appears to have
bottomed out in the upper 980s well inside 130w. This has produced
high winds along the coast and in the higher coastal mountains... and
Astoria Airport even reported a peak wind of 62 miles per hour moments ago.
Windy conditions spread inland with a few gusts having reached around
40 miles per hour so far.
When the cold front moved through the interior earlier this
morning...a line of thunderstorms developed and gave a burst of rain
around a quarter inch or so to many locations. Rainfall has been a
bit subdued as often happens with these stronger wind storms as
indicated in our afd yesterday. The bent back occlusion will clip the
northwest part of our area with some better shower coverage through
the morning and into the early afternoon...but the remainder of the
area showers will be more scattered. A bit of sunshine mixed could
allow temperatures to rise into the middle and upper 70s...with an 80 not out
of the question near Eugene. As a result...a slight chance of thunder
will continue this afternoon.
The surface low is forecast to be around Puget Sound sound and Vancouver
Island by 21z or 2 PM...and the gradients will be weakening
considerably by then. The winds in the south part of our area should
be easing by noon...and the north part by around 2 PM or so.
Attention then turns to the next front...currently crossing 130w on
infrared satellite imagery and partially merging with the bent back
occlusion of our current strong surface low. This front will reach
the coast in the afternoon and early evening and spread through
southwest Washington and northwest Oregon tonight. This front is
somewhat convective in nature...and there will be a slight chance of
thunder with it along the coast and in the north interior zones
again. There is some wind with it...especially near the coast... but
not as windy as today. Look for gusts to around 40 miles per hour at the
normally windier exposed locations along the coast this evening.
Onshore flow will continue behind the front on Sunday for decent
shower coverage through the day...especially over the mountains.
Monday will continue to see onshore flow with a mixture of clouds and
sunshine and below normal temperatures. The main threat of showers on
Monday will be in the north and near the higher terrain. Tolleson
Long term...no changes. Previous discussion follows...
Monday night through Friday...the Fall-like weather pattern will
continue next week with primarily cooler than normal
temperatures...cloudy conditions...and chances for additional rain. A
trough will remain near the Pacific northwest coast through most of
the period with some rain at times...especially during the early and
middle parts of next week. Little change made to the current
Aviation...ceilings are starting to break up behind the front this
morning...with VFR conditions across the area. Generally VFR
conditions continue through this afternoon. Scattered showers across
the area through the afternoon could briefly drop ceilings to MVFR. There
is a slight chance of thunderstorms and rain at northern taf sites until after 00z. S
winds are gusting to 50 knots at coastal taf sites this am...and will
weaken this afternoon to 20 to 25 knots by this evening. At inland taf
sites...S winds are gusting to 35 knots and could gust up near 40 knots
through early this afternoon...with strongest winds at northern taf
sites. Ceilings lower back to MVFR tonight for the overnight hours as a
weaker front brings more rain across the area.
Kpdx and approaches...VFR conditions through early this evening.
Scattered showers through the afternoon could drop ceilings to MVFR.
Slight chance of thunderstorms and rain until around 00z this evening. S winds gusting
to 35 knots...starting to ease around 21z. After 00z...rain increases
for overnight hours lowering ceilings to MVFR until Sunday morning.
Marine...S winds gusting to 45 to 50 knots over the waters this
morning...bringing seas up to 14 to 18 feet. Winds will start to
gradually weaken...back down to solid gales by noon. Seas will stay
up around 13 to 15 feet through the early afternoon hours with winds
around 25 to 35 knots gusting up to 40 to 45 knots. Later this evening...
seas will lower to 10 to 12 feet and winds decrease to 15 to 20 knots
gusting to 25 knots out of the SW. Will probably need a Small Craft
Advisory for winds and seas to continue through the overnight hours
until Sunday morning. Seas during this time will hover around 10 feet
and winds will continue to gust to 20 to 25 knots.
Unsettled weather continues into next week with seas staying around 6
to 9 feet through at least midweek. -McCoy
or...Wind Advisory until 3 PM PDT this afternoon for greater
Portland metropolitan area-lower Columbia.
High Wind Warning until 1 PM PDT this afternoon for central
Wind Advisory until noon PDT today for central Willamette
Valley-south Willamette Valley.
High Wind Warning until 2 PM PDT this afternoon for Coast Range
of northwest Oregon-north Oregon coast.
High Wind Warning until noon PDT today for central Coast Range
of western Oregon.
Washington...Wind Advisory until 3 PM PDT this afternoon for Greater
Vancouver area-I-5 corridor in Cowlitz County.
High Wind Warning until 3 PM PDT this afternoon for Willapa
High Wind Warning until 2 PM PDT this afternoon for South
Pz...Storm Warning until noon PDT today for coastal waters from
Cape Shoalwater Washington to Florence or out 60 nm.
Gale Warning until 8 PM PDT this evening for coastal waters
from Cape Shoalwater Washington to Cascade Head or out 60 nm.
Small Craft Advisory for rough Columbia River bar until
midnight PDT tonight.
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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.