Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 272136

Area Forecast Discussion
National Weather Service Portland OR
235 PM PDT Thu Apr 27 2017

.SYNOPSIS...Strong NW flow aloft will continue showers through this
evening. High pressure will support dry weather Friday and Saturday
with slightly warmer afternoon temperatures. A cold front will
bring light rain to extreme SW Washington late Saturday afternoon
spreading south across NW Oregon Saturday night and Sunday morning.
The upper level ridge will re-build early next week for more days of
dry weather, and temperatures will likely warm into the 70s mid next


.SHORT TERM...(Tonight through Sunday)...A 140+ kt 250mb Pacific jet
will maintain showers over SW Washington and NW Oregon this through
this evening. Some of the showers this afternoon and evening will be
rather heavy and provide a quick burst of 0.10-0.15 inch of rain.
These showers are moving fairly quickly though, which should reduce
any threats for minor flooding with the heavy showers. Snow levels
are above the Cascade passes, but would not be surprised if some of
the heavier showers bring a mix of rain and snow down to just below
the Cascade passes at times.

The jet will weaken and move inland tonight as an upper level ridge
builds over the Pacific NW, and showers will end. This will mark the
beginning of a brief dry period for the Portland forecast area with
dry weather for Friday and most of Saturday. Daytime highs will be
slightly warmer Friday and Saturday with temperatures peaking in the
low 60s on Friday and the mid 60s on Saturday.

Clouds will increase north of Salem late Saturday morning, and south
of Salem late in the afternoon as a cold front approaches from the
north. The front will bring rain to extreme SW Washington late
Saturday afternoon or early Saturday evening, and spread south
Saturday night and Sunday morning down to Lane County. This front
will move through quickly with showers ending Sunday evening.
Rainfall totals will range between 0.10 to 0.30 from Saturday
afternoon through Sunday afternoon with the higher amounts over the
higher terrain. Snow levels should be well above the Cascade passes.

.LONG TERM...Sunday night through Thursday...A few residual showers
may continue Sunday night in the wake of the weak front, mostly in
the northern and eastern portions of the forecast area. A low
pressure system moving into the B.C. coast will bring an associated
front into the Pacific Northwest, spreading clouds into the region.
Some timing differences remain for when this disturbance slides
across the forecast area - either Monday or Monday night - so have
left a slight chance of showers during this period. It appears the
best moisture will be to the north of the area, and any potential
rainfall will be rather minimal. Dry and warmer conditions then set
up for the mid-week time period as an upper level ridge amplifies
over the Pacific Northwest. While 500 mb heights and 850 mb
temperatures would suggest that the mid 70s are not out of the
question for afternoon high temperatures, have held the forecast a
few degrees cooler for now - more in line with model consensus,
given the relatively large spread. By late Thursday, the upper ridge
axis shifts eastward into the Great Basin, which opens the door for
the next frontal system to approach the coastline of the Pacific
Northwest with increasing clouds and possibly a return of
precipitation chances. Cullen

.AVIATION...Showers are at their peak for today and will
dissipate this afternoon and evening as high pressure starts
building offshore. Strongest showers are now east of the TAF
terminals and conditions will primarily remain VFR, only
occasionally falling to MVFR hereafter. Skies will clear
overnight and light winds will allow a stratus deck at 015-025
to develop beginning around 12z. Should see that layer clear by

KPDX AND APPROACHES...VFR conditions through this evening, with
cigs running around 4000 ft. Scattered showers may bring brief
MVFR under heavier showers. A stratus deck around 020 will
develop over the field beginning around 13z then clear around
28/18z. /JBonk


.MARINE...High pressure is building offshore then moving inland
through Saturday. Surface thermal low pressure will build north
from California and enhance the northerly flow along the coastal
waters. Could see SCA level wind gusts reach the central oregon
waters by Friday evening. A frontal system flattens the upper
ridge Saturday evening and night for a brief turn of winds
backing southerly and likely high enough to warrant a SCA for
winds. High pressure strengthens next week with winds veering
northerly behind the front and likely remaining so into early
next week. The surface thermal low will strengthen further and
probably begin a few day pattern of afternoon and evening gusty

Seas holding at 8 to 9 ft today into early this evening, then
seas will slowly subside. They will build again Saturday night
under wind waves associated with the front. They then will sit at
7 ft or less for the remainder of the forecast period. /JBonk


PZ...Small Craft Advisory for Rough Columbia River Bar until 8 PM
     PDT this evening.

     Small Craft Advisory for Rough Columbia River Bar from 4 AM to
     8 AM PDT Friday.


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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. is the U.S. government's official web portal to all federal, state and local government web resources and services.