Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 282152
Area Forecast Discussion
National Weather Service Portland OR
251 PM PDT Sun Aug 28 2016
.SYNOPSIS...A broad upper trough off British Columbia will continue
through the weekend, then dig south along the coast early in the
coming week, then swing onshore late week. This will maintain onshore
flow over the local area for at least night and morning low clouds
and cooler temperatures. Expect showers especially Tuesday night and
.SHORT TERM...This afternoon through Wednesday...Upper low pressure
off the northern British Columbia coast will deepen and drift south
over the next few days as high pressure over the southwest US
strengthens, placing the PacNW under southwest flow aloft through the
short term. Expect coastal fog and drizzle at times with interior
areas marked by varying amounts of morning clouds and afternoon sun
with better chances of clouds to hang on during the day across the
northern CWA. Will see some drizzle or very light rain across much of
the area beginning as early as Monday night as a weak cold front
approaches. Chances for generally light rain continue through the day
Wednesday as the front dissipates over the local area.
Models show another upper low swinging into Northern California and
Oregon on Tuesday, turning upper flow a bit more southerly and
brining some chance for thunderstorms near the Oregon Cascade crest
Tuesday afternoon. At this point it appears there would be enough
moisture locally to produce some rain with any thunderstorms.
Temperatures will fall below daytime normals inland after today but
remain above overnight norms as the southwesterly flow air mass
regime keeps dew points in the 50s. Overall it will be a cool and
moist first half of the week. Bowen
.LONG TERM...Wednesday night through Saturday...Continued cooler and
cloudier with periods of light rain will be the general rule for the
second half of next week as various impulses rotate across the region
around the base of the mean trough to the north. However, timing and
strength differences remain among the forecast models with a fair
amount of spread among ensemble members. As a result, less confidence
in the precise periods of higher chances of rain. Regardless,
afternoon high temperatures will remain in the low 70s inland during
the extended period, several degrees below normal for this time of
year. With cool and moist conditions, it will feel like an early
taste of fall. However, overnight low temperatures will be more
seasonable, in the 50s. Bowen/Cullen
.AVIATION...Marine stratus has cleared all terminals except for
KONP where cigs will continue to bounce between IFR and MVFR. Low
stratus will build northward up the coast again tonight and will
arrive during the evening at KONP and near midnight at KAST.
Marine layer will be deep enough tonight for stratus to infiltrate
the Willamette Valley. It appears stratus will sneak through the
coast range gaps in the south Valley first and stream northward.
In addition, some stratus will develop in the north Oregon Cascade
near TTD around 12Z and expand south and westward.
KPDX AND APPROACHES...VFR conditions for the remainder of today.
MVFR cigs expected after 12Z Monday. /Bentley
.MARINE...Benign marine weather concerns this week. Models have
come to a better agreement that winds will remain mostly out of
the south through the week and even into next weekend. A period
of stronger gusty winds is possible on Tuesday ahead of a cold
front that will move through Wednesday night, but otherwise no
small craft for winds concerns across our waters.
Seas will remain 5 feet or less through the weekend due to light
winds and a lack of any significant storm systems in the north
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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.