Area Forecast Discussion
Issued by NWS Portland, OR

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910
FXUS66 KPQR 232156
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
256 PM PDT Wed Aug 23 2017

.SYNOPSIS...A weak front will bring a chance for some very light
rain, increased clouds, and cooler temperatures through Thursday.
High pressure aloft quickly rebuilds across the Pacific Northwest
Saturday, for a return of very warm temperatures by the end of the
weekend. Hot conditions will remain through the first portion of next
week as the upper level ridge remains in place.

&&

.SHORT TERM...Tonight through Saturday...A somewhat complex cloud
pattern evident on visible satellite imagery this afternoon with
several cloud layers apparent. Lower clouds continue to scatter and
mix out along most of the area, though a few pockets of overcast
stratus remain along the central portions of the Oregon coast. A line
of clouds associated with southwest flow aloft ahead of an
approaching upper trough has been thick enough to produce some light
sprinkles across portions of the Willamette Valley this afternoon.
Expect this to continue as the line slowly advances east-northeast
across the region, so have added sprinkles to the forecast for the
eastern half of the Willamette Valley into the foothills through the
evening.

A weak front currently offshore will slide across the forecast area
overnight through early Thursday. This will increase the spatial
extent of cloud cover overnight through early Thursday, as well as
bring some chances for very light rain across the region overnight.
Still expect amounts to be very light, but most locations will likely
see at least trace amounts of rain. With the deeper cloud layer, have
also maintained mention of light drizzle for much of the day
Thursday. Forecast model soundings support a rather deep saturated
layer, and with the approach of the upper trough, suspect that there
will be enough support for some ongoing drizzle through the day.
While accumulations look to be little, if any, would not be surprised
to see one or two sites reach 0.05" total accumulation if the
saturated layer is as deep as models suggest. Thursday will be on the
cooler side, with afternoon high temperatures in the mid 70s across
the interior.

Shortwave ridging slowly pushing eastward into the Pacific Northwest
should warm temperatures closer to climatological normals on Friday,
with widespread sunshine on Friday. An even warmer day in store
across the interior on Saturday as 500 mb heights climb to near 590
dam and 850 mb temperatures reach near 20 degrees C per latest model
guidance.   Cullen

.LONG TERM...Saturday night through Wednesday...Temperatures remain
rather warm for the start of next week, with at least a few days
reaching into the 90s across the interior portions of the forecast
area.  Models have fluctuated a bit with respect to the placement of
the thermal trough through the weekend, but it appears likely that
offshore low-level winds will develop at some point late Saturday
through Monday, which will be responsible for additional warming.
This shift in winds will also allow some smoke from nearby wildland
fires in the Cascades to filter back into the region Sunday and
Monday. Have maintained a dry forecast through the middle of the week
for now, though there will perhaps be a window for some thunderstorms
to develop as the upper level ridge breaks down around midweek.
Cullen

&&

.AVIATION...The coast will continue to see a mix of flight
conditions this afternoon as marine stratus continues to play
peek-a-boo with the terminals. Expect stratus to eventually
consolidate at the coast this evening with conditions becoming
predominately MVFR, but local IFR fog is possible. Otherwise, the
interior will remain VFR through tonight. A weak front will move
across the forecast area late tonight/early Thu and bring reduced
cigs along with some light rain/drizzle to the forecast area.
Conditions in the interior will likely become VFR Thu afternoon,
but the coast will likely remain below MVFR.

KPDX AND APPROACHES...VFR through tonight. A weak front will
impact the terminal late tonight/early Thu and bring a period
of MVFR cigs and possibly some light rain/drizzle. Conditions
look to become VFR by Thu afternoon. /64

&&

.MARINE...A decaying cold front will move across the waters later
this evening and tonight. Post-frontal winds may bring a brief
period of advisory gusts late tonight, but given the short
duration of the strongest wind decided to continue to not
headline any hazards. High pressure rebuilds behind the front
late tonight, with thermal low pressure strengthening as we go
into the weekend. Expect winds to generally remain below 20 kt
through Thursday. SCA gusts to 25 kt are possible Friday over
the central waters as the thermal low builds north so expect
marine headlines to be issued in the coming future. Widespread
SCA gusts around 25 to 30 kt are possible over the weekend as the
thermal low gets stronger so additional headlines will be needed.

Seas will generally be around 4 to 6 ft through the period, but
could build to around 7 ft and become steep at times this weekend
as the winds increase. Not expecting square seas this weekend,
but if the winds are slightly stronger we may need to consider a
headline. /64

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.

&&

$$

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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.



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