Area Forecast Discussion
National Weather Service Portland OR
145 PM PDT Tue Jun 27 2017

.SYNOPSIS...Dry, onshore flow continues through the forecast period.
An upper ridge will traverse the area Thursday and Friday, bringing
mostly clear skies and slightly warmer temperatures. Otherwise, the
seasonable pattern of morning clouds and afternoon sun continues
through the weekend.
&&

.SHORT TERM...Tonight through Saturday...An upper ridge near 135W
keeps northwest flow over the region through Wednesday. A weak but
dry shortwave in the northwest flow moves over the area early
tomorrow, so expecting another robust marine layer in the morning.
The upper ridge will move closer to shore later Wednesday and
Thursday, and traverse western OR/WA Friday morning. While offshore
flow never develops, the marine layer should be considerably more
shallow both Thursday and Friday, for mostly sunny skies and
seasonably warm temperatures. Saturday sees the ridge flatten and
move eastward, bringing a benign westerly flow and thickening marine
layer, for morning clouds followed by afternoon sun. DRB

.LONG TERM...Saturday night through Tuesday...Westerly flow continues
through the extended period. A couple of embedded, low amplitude
ridge/trough systems pass mostly to the north of area, with GFS/GEFS
timing favoring weak shortwaves late Saturday and again on Monday.
The main result will be a thickening marine layer over the weekend
and particularly on Monday. Depending on the strength of these
shortwaves, some drizzle/very light precipitation along coastal zones
is not out of the question. That said, the odds favor a dry forecast
with many dry ensemble members through the period. Temperatures
should be close to seasonal normals this weekend, and near or
slightly below normal early next week. DRB

&&

.AVIATION...Marine stratus has lifted or cleared in most areas
for VFR conditions this afternoon. MVFR cigs will clear south of
SALEM by 22z. The coast has a mix of VFR and MVFR early this
afternoon, and will become solid MVFR early this evening. Cigs
may lower to below 1000 feet along the coast tonight. A
shortwave upper trough moving over the area tonight will maintain
a deep marine layer and expect coastal stratus to move inland
into the Willamette Valley and Cascade foothills early Wednesday
morning (~12z). Inland areas should clear to VFR Wednesday
afternoon.

PORTLAND AND APPROACHES...VFR conditions this afternoon evening.
Marine stratus will return MVFR cigs very early Wednesday morning
(11-13z), and clear to VFR Wednesday afternoon. ~TJ

&&

.MARINE...A persistent surface pressure pattern with high
pressure over the NE Pacific and a thermal low in Northern CA
will result in little changes to the overall marine weather for
through the weekend. N-NW winds will mostly remain below 25 kt,
although there will be a few gusts around 25 kt in the waters
beyond 20 nm this afternoon and evening. Surface high pressure
increases a tad on Sunday and the north winds will likely
strengthen to 25 kt, especially south of Cascade Head.

A combination of wind wave and fresh swell will create choppy
seas with heights 5 to 8 feet and dominant periods around 8
seconds today and Wednesday. A strong ebb Wednesday morning may
steepen the seas nearshore (0-5 nm) a few hours around the 845 AM
ebb. A weak low moving across the Gulf of Alaska Wednesday night
and Thursday will increase wave periods to around 10-11 seconds
beginning early Thursday. ~TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for Rough Columbia River Bar from 8 AM to
     11 AM PDT Wednesday.

&&

$$



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.