Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 172049

Area Forecast Discussion
National Weather Service Portland OR
149 PM PDT Tue Jul 17 2018

.SYNOPSIS...Gradual cooling is expected in the interior each day
through the end of the week as onshore winds and a deepening marine
layer increases the marine influence. An upper ridge builds over the
weekend with inland temperatures warming back into the 90s early next


.SHORT TERM...Tonight through Friday...Marine clouds have retreated
to the coast early this afternoon and will continue to retreat to
near the beaches this afternoon. Clear skies inland continue to the
dry and warm weather with little change in the temperatures from 24
hours ago. Although the temperatures are similar early this
afternoon, a slightly cooler airmass (mostly mid and high levels)
should result in high temperatures late this afternoon a few degrees
cooler than yesterday.

Satellite imagery shows extensive stratus offshore and over the NE
Pacific building further confidence that marine clouds will quickly
return to the coast this evening (if they clear at all). A passing
upper trough will result in a deeper marine layer overnight and allow
the marine clouds to move further inland Wednesday morning. AM fairly
confident that clouds will move up the lower Columbia River Valley
into the north Willamette Valley early Wednesday morning, then move
further south into parts of the central Willamette Valley.

This inland intrusion of marine air will result in a much cooler
afternoon on Wednesday with inland temperatures peaking in the 80s
rather than the 90s of late. Expect around 10 degrees of cooling
north of Salem and around 5 degrees of cooling south of Salem.

Another upper trough Wednesday night and Thursday will deepen the
marine layer a bit more for slightly more expansive inland clouds
Thursday morning and 3-5 degree cooler temperatures Thursday

A closed upper low drops south from the Gulf of Alaska into British
Columbia Thursday night and Friday sustaining a deep marine layer,
inland clouds and slightly cooler afternoon temperatures. THis will
likely be the coolest day of the week with the temperatures in the
Willamette Valley peaking in the upper 70s to low 80s. ~TJ

.LONG TERM...Friday night through Wednesday...An upper level trough
continues to move through the area on Fri. The 12z GFS and 12z Euro
are showing a slight cooling trend for Fri. However, Fri night into
Sat, the models agree that this cooling trend will be short lived.
As both models are agreeing that a ridge will start to push the
trough out of the area on Sat, which will lead towards a warming
trend for the area. What needs to be noted is that the GFS is
showing a slower transition into the ridge than the Euro currently.
This could change as the models out into the extended time frame
have been diverging in the past model runs. However, both models
show the ridge flattening out, and maintaining the warming trend
through the middle of the week. /42

.AVIATION...Marine stratus is hugging the coastal strip this
afternoon. The stratus will likely thin and lift for a few hours this
afternoon improving conditions to VFR. However, the stratus will
move back into the coastal TAF sites late this afternoon or
early evening bringing MVFR cigs. The ceiling will lower to IFR
by morning with some patchy fog. Expect the stratus to move up
the Columbia River to about KPDX-KTTD early Wed morning in the
10z- 14z time frame bringing MVFR cigs. There is also some
potential for some low clouds to get close to KEUG early Wed
morning, but likely remain scattered.

PDX AND APPROACHES...VFR conditions through the evening with
breezy NW winds developing late this afternoon and evening. MVFR
cigs expected to develop around 12z-14z Wed morning.


.MARINE...A typical summer-time pattern will persist for the
next several days. High pressure will reside over the NE Pac,
with a thermally-induced trough over the northern California and
southern Oregon. This will maintain northerly winds over the
coastal waters through next weekend. Winds should generally
remain 20 kt or less through midday Wed. The winds will become a
bit stronger Wed afternoon and evening with gusts near 25 kts
over the central OR waters, mainly south of Cascade Head. Winds
then strengthen further Thu afternoon and evening and remain
gusty through the weekend. Expect gusts of 25 to 30 kt in the
afternoons and evenings with a little less wind during the
morning hours.

Seas will remain around 5 to 6 ft through Thursday. Seas look to
build to around 7 to 8 ft near the end of the week and over the
weekend and will become choppy and potentially steep as the gusty
northerly winds return. tw

PZ...Small Craft Advisory for winds from 2 PM Wednesday to 5 PM PDT
     Thursday for Coastal Waters from Cascade Head OR to
     Florence OR out 60 NM.


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