Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 261128 AAA

Area Forecast Discussion
National Weather Service Portland OR
427 AM PDT Mon Jun 26 2017

.SYNOPSIS...High pressure over the Pacific Northwest will weaken over
northwestern Oregon and southwestern Washington. A marine surge will
continue to push inland overnight, for much cooler temperatures
today. There is a slight chance for some high-based thunderstorms
over the portions of the forecast area on Monday. Dry northwesterly
flow sets up later this week across the region, bringing more
seasonable temperatures and a pattern of morning clouds and afternoon


.SHORT TERM...Today through Thursday...After a very hot (and
record-setting, in some cases) weekend across the region, it is safe
to say that our stretch of heat has ended with a solid influx of
marine air into the interior reaches of the forecast area. In what
will certainly be a welcome relief to many, temperatures early this
morning range from the upper 50s to lower 60s. Yesterday brought new
record high temperatures for the day at Hillsboro (100) and Vancouver
(101), as well as a tied mark at Portland airport (101). Also of
note, last evening`s 00Z upper air sounding at Salem observed an 850
mb temperature of 24.2 degrees C, which sets a new maximum mark among
the 00Z/June 26 soundings [records date to 1957].

A few areas of strong thunderstorms developed over the Cascades late
last evening, but did not persist much past 11 PM. However,
persistent convection has been noted along the southern Oregon coast
and adjacent coastal waters overnight, currently reaching as far
north as Charleston or North Bend. Models continue to indicate some
elevated instability in association with an upper level shortwave
trough approaching the region. Latest SPC mesoanalysis continues to
indicate decent mid-level lapse rates across the region and models
project this to move across the region through the first part of the
day today. Forecast models continue to depict the best dynamics
remaining to our south and east, but some high resolution models so
suggest the possibility for thunderstorms remains across the forecast
area through late morning. One model in particular, the HRRR,
continues to suggest a line of stronger showers across the northern
half of the forecast area by the afternoon, but this does appear to
be a bit aggressive among the full range of guidance. The slight
chance mention of thunderstorms in the forecast across much of the
area does continue through 18z, but have restricted mentioned after
this time to primarily the Cascades/Foothills in Lane County.

Elsewhere, considerably cooler afternoon temperatures on Monday
across the interior as compared to the last few days. Northwesterly
flow aloft sets up over the region for the remainder of the first
half of the week. Expect increased marine cloud cover and even cooler
temperatures Tuesday and Wednesday. With the thicker marine layer in
place, clearing may be delayed until later in the afternoon with
perhaps a few areas of morning drizzle possible along the north coast
and/or in the Cascade foothills. Forecast models remain in rather
good agreement for Thursday, with the next ridge building over the
region. This will bring warming temperatures and skies will likely
trend towards mostly sunny earlier in the morning, though onshore
low-level flow will maintain at least some clouds.   Cullen

.LONG TERM...Thursday night through Monday...Little change to the
overall pattern into Friday as the upper ridge migrates east across
the Pacific Northwest and east of the Cascades later Friday. This
should bring afternoon high temperatures a little warmer over the
interior, but not much beyond 80F as heights only build to 582 dam.
Models begin to diverge a bit into the weekend, but at least moderate
confidence in the upper trough bringing increasing clouds and
probably some light showers at some point over the weekend. High
temperatures will trend closer to seasonal normals.   Cullen


.AVIATION...Onshore low level flow with LIFR to low MVFR
conditions at the coast in marine stratus. Satellite presentation
of the stratus is partially obscured by higher clouds. Though it
appears to have pushed to the east slopes of the coast range and
up the lower Columbia River to KKLS as of 10Z. Still think MVFR
cigs will reach inland TAF sites in the 14-16Z time frame then
lift to a low VFR after 19Z continue to rise through 00Z and
become SCT-BKN around 4000-5000 ft.

An approaching upper level trough will bring a slight chance for
elevated thunderstorms this morning, with the best chances over
the southern Willamette Valley and Lane County Cascades.
Thunderstorm chances should be limited to the Cascades in Lane
county this afternoon before ending this evening.

KPDX AND APPROACHES...VFR through 14Z the chances for MVFR cigs
becoming likely and lasting through 18-19Z. Cigs initially start
between 1000 and 1500 feet the lift to around 3000-3500 feet
midday. Cigs should further lift to around 4500-5000 ft near 00Z.


.MARINE...A weak trough over the waters will give way to building
high pres late today and remain through most of next week. This
will bring a return to northerly winds. The winds may come close
to Small Craft Advisory threshold during the afternoon and
evening on Tue and Wed, but it looks very borderline. The high
pres weakens some late next week.

Seas to continue well below 10 ft for the next several days.
Currently seas are around 5 to 6 ft with a 7 to 8 second dominant
period. But near the 60 nm border seas by be closer to 7 ft at
7-8 seconds for today. Seas will be somewhat choppy but does not
look like it will exceed advisory criteria. There is the
potential for another uni-wave set-up Tue and Wed which usually
brings fairly steep choppy seas.





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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This 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.