Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 201112
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
411 AM PDT Fri Apr 20 2018

.SYNOPSIS...Dry and mild weather today before a cold front spreads
light rain and Cascade snow across the region late tonight. Some
showers may linger over the Cascades Saturday morning, but otherwise
the day will be dry, but cool. Dry weather continues Sunday into next
week. Temperatures are expected to warm into the 70s Monday and
Tuesday as a thermal trough settles over NW Oregon and offshore flow
develops.

&&

.SHORT TERM...Today through Monday. Dry and mild weather continues
today with increasing high clouds ahead of an approaching front. A
warm front brushes by to the north this afternoon with little impact
to the weather.  The cold front will produce light rain along the
coast this evening moving inland late tonight. Snow levels will be
around 4500 feet for the south Washington Cascades and 6000 feet for
the Cascades of Lane County when the precipitation arrives tonight.
He snow levels then lower to 3500-4500 feet Saturday morning as light
showers linger over the Cascades. The highest forecast rainfall
amounts this afternoon through Saturday afternoon are around 0.20 inch
along the north coast, the Willapa Hills, and the south
Washington Cascades. The Willamette Valley, especially south of
Salem, are not expected to see much rain (0.01-0.05 inch). THe
Cascades can expect a few inches of new snow with no expected impacts
for the Cascade passes.

A few showers will linger over the the Cascades and across extreme SW
Washington Saturday morning, but most areas west of the Cascades will
remain dry. Cool and cloudy conditions with onshore flow is  expected
Saturday in the wake of a cold front. Dry weather continues Sunday
with surface high pressure building over the area. A shortwave upper
trough may keep some clouds around and somewhat limit heating, but
the afternoon temperatures will still peak slightly above the
seasonal normals.

A sharp upper ridge moves over the Pacific NW Sunday night and Monday
continuing dry weather. A thermal trough develops along the coast
Sunday night and persists Monday for offshore flow and warmer
temperatures. Much of the area will warm into the 70s Monday
afternoon with the coast likely peaking in the upper 60s.~TJ

.LONG TERM...No Changes. Previous discussion follows...Monday night
through Thursday...Models have come into better agreement regarding
the weather next week, now showing continuing high pressure and dry,
warm conditions. Even the 12Z GFS is on board with continued warming
Tuesday and Wednesday with MEX guidance showing temperatures as warm
as the upper 70s in the valley on Wednesday. Haven`t gone that warm
with the forecast, but do have 70s inland Monday through at least
Wednesday.

Where the models do still diverge is with the track of an upper low
pressure system which moves south off the west coast through midweek.
After that, the GFS continues to spin the low well off the California
coast through the end of the week while the ECMWF brings the low into
southern California. Any shower or thunderstorm chances in the
Cascades next week will depend on the exact track of the low, but
have kept mentionable chances out of the forecast for now. This means
that after Saturday evening, there are currently no mentionable rain
chances anywhere in the local forecast area through the rest of the
7-day forecast. Vampires beware. Here comes the sun.

&&

.AVIATION...High pres with dry northerly flow over NW Oregon and
SW Washington. Next front will slowly approach the coast later
Fri and Fri night. Will see increasing mid and high clouds over
the region later tonight through Fri. Light rain will begin
around 02z near KAST and spread inland to KPDX around 07z.Expect
mostly vfr conditions but lowering to mvfr occasionally along the
coast and the northern valleys through 15z Saturday when the
front passes.

KPDX AND APPROACHES...High pres with dry air mass tonight into
Fri. Mid/high clouds will gradually increase Fri. Rain likely
developing around 07z with VFR conditions with a 40 percent
chance of mvfr after 09z. Schneider

&&

.MARINE...High pressure this morning will give way to an
approaching trough of low pressure and associated cold front. the
front will move over the coastal waters late this afternoon and
tonight with Small Craft Advisory winds spreading form the outer
waters early this evening to the inner waters before midnight.
This front will be fairly fast moving with winds shifting to WSW
behind the front and dropping off by Saturday morning. A west
Swell will move into the waters with building seas and a
moderately long period. Small Craft Seas will continue on
Saturday and slowly diminish Saturday evening. High pressure will
rebuild on Sunday with more spring/summerlike NW winds
developing over the waters. Thermal troughing will develop as
high pressure builds on Tuesday and Wednesday and the inland
areas warm up. This could give Small Craft Advisory force winds
to the waters Tuesday and Wednesday. Schneider

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
PZ...Small Craft Advisory for winds from 11 Pm this evening to 8 AM
     PDT Saturday for Coastal waters from Cascade Head to Florence OR
     out 10 NM.

     Small Craft Advisory for hazardous seas from 5 AM to 5 PM PDT
     Saturday for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 10 NM.

     Small Craft Advisory for winds from 6 PM this evening to 11 AM
     PDT Saturday for Waters from Cape Shoalwater WA to Cascade
     Head OR from 10 to 60 NM.

     Small Craft Advisory for hazardous seas from 11 PM this evening
     to 5 PM PDT Saturday for Waters from Cape Shoalwater WA to
     Florence OR from 10 to 60 NM.

     Small Craft Advisory for winds from 6 PM this evening to 8 AM
     PDT Saturday for Waters from Cascade Head to Florence OR
     from 10 to 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 10 AM
     PDT this morning.

     Small Craft Advisory for Rough Columbia River Bar from 7 PM
     this evening to 5 AM PDT Saturday.

     Small Craft Advisory for winds from 8 PM this evening to 11 AM
     PDT Saturday for Coastal waters from Cape Shoalwater WA to
     Cascade Head OR out 10 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.



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