Area Forecast Discussion
Issued by NWS Portland, OR

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638
FXUS66 KPQR 280414
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
914 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
less morning low clouds and slightly warmer afternoon temperatures.
Otherwise, the seasonable pattern of morning clouds and afternoon sun
continues through the weekend.

&&

.SHORT TERM...Tonight through Saturday...Forecast appears to be in
good shape, with classic summertime weather expected for the next
week across the Pacific Northwest. Only minor changes were made with
the evening update, mainly to allow for a bit more morning low
cloudiness Wed/Thu mornings.

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. Model soundings suggest a robust marine layer about
3000-4000 ft deep around 12z Wed, which should allow stratus to push
all the way to near the Cascade crest. Coastal areas may see some
spotty drizzle due to the deep onshore flow. Clouds will be slow to
clear, but eventually most of the forecast area should break into a
mostly sunny afternoon with seasonable temps in the 70s inland
valleys and 60s along the coast.

The upper ridge will move closer to shore later Wednesday and
Thursday, then traverse western OR/WA Friday morning. While offshore
flow never develops, the upper ridging should compress the marine
layer to 1500-2000 ft Wed night/Thu morning. This should lead to a
less extensive marine push, with any morning clouds likely quicker to
burn off Thu morning. As a result of this and 850 mb temps warming to
around +14 to +15 deg C, temps should warm up 5-10 degrees
inland...with highs in the lower to mid 80s in the valleys. Even less
stratus is expected Friday morning as the upper ridge axis moves
across the Pac NW. However, flow remains onshore, so temps should be
similar or just slightly warmer Friday.

Saturday sees the ridge flatten and move eastward, bringing a benign
westerly flow and thickening marine layer, for morning clouds
followed by afternoon sun.  Weagle/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...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 MVFR stratus
to move inland into the Willamette Valley and Cascade foothills
early Wednesday morning (~12z). Inland areas should clear to VFR
Wednesday afternoon.

KPDX AND APPROACHES...Marine stratus will return MVFR cigs very
early Wednesday morning (11-13z), and clear to VFR Wednesday
afternoon. ~Bowen/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
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 evening. The next chance for winds of that
strength will be when 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. ~Bowen/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.

&&

$$

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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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