Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 290316 AAA

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
816 PM PDT Sun May 28 2023

Updated aviation discussion

.SYNOPSIS...Persistent onshore flow will bring seasonable to slightly
above normal temperatures over the next week. Temperatures will peak
around 80 degrees for Memorial Day before cooling back to near normal
for mid week. Dry conditions look to continue through at least
Saturday aside from a 10 to 20% chance of showers and thunderstorms
in the Lane County Cascades during the afternoon and evening hours


.DISCUSSION...Sunday through Saturday night...Weak upper level high
pressure is building over the PacNW today as a closed low to our
south is slated to move southwest along the northern to central
California coast. Instability wrapping around the north of the closed
low will barely push into the southern corner of the CWA, creating a
10-20% chance of showers and thunderstorms in the Cascades of Lane
County this afternoon and evening. Stronger showers and thunderstorms
are forecast to stay south and west of the forecast area. Otherwise,
dry weather with onshore flow will be the persistent forecast through
the upcoming week. Temperatures today and tomorrow will be the
warmest of the week with valley locations in the mid to upper 70s,
pushing 80 for Memorial Day tomorrow.

Ensemble guidance is in good agreement that the southern edge of
longwave troughing from a parent trough situated in the Gulf of
Alaska will push into the PacNW Tuesday with multiple shortwaves
along the flow moving over the region into Friday. The main impact of
this will be temperatures cooling back to near normal for late
May/early June, which is low 70s across the Valley. Additionally,
surface pressure gradients will tighten each afternoon and evening,
causing an increase in onshore winds, especially along the coast and
the Columbia River. Cloud cover will increase, and depending on how
long stratus lingers inland, some Valley locations could struggle to
reach 70 degrees for the high temperature Wednesday and Thursday. NBM
indicates only about a 35-55% chance of locations in the Willamette
Valley and into Vancouver, WA reaching 70 degrees these days.

Beyond Thursday, ensemble guidance becomes a little more uncertain,
but the overall consensus is the upper trough currently in the Gulf
of Alaska will deepen significantly over the eastern Pacific Friday
into the weekend, and strong upper level high pressure building over
the Midwest. With NW Oregon and SW Washington stuck in between this
pattern, temperatures are expect to warm, but just how much
temperatures will warm will depend on how far west high pressure can
spread. For now will still with the NBM deterministic forecast, which
indicates warming into the upper 70s by Friday and low 80s for the
weekend across the valley and upper 60s by Friday and 70s for the
weekend for the coast and mountains. -HEC


.AVIATION...Low level flow dominated by high pressure that sits
offshore into western Washington. As such, will maintain north to
northwest flow closer to the surface. Most of the marine stratus
will stay along the coast and over the Pacific, especially to
north of KTMK. But, will see that stratus push back onshore this
evening, though may stay just offshore from Newport southward
until late tonight.

Farther inland, VFR under variable high clouds. Tonight similar
to Sat night/Sun am, with marine stratus surging up the Columbia
River again, reaching PDX/VUO metro by daybreak Mon. Expecting
areas south of Aurora will stay mostly clear.

For detailed Pac NW aviation weather information, go online to:

KPDX AND APPROACHES...VFR under variable high clouds into tonight.
Am expecting another round of MVFR stratus to arrive towards
daybreak Monday, and like Sunday, will take good part of morning
to break back to VFR and scattered clouds. -BMuhlestein/Rockey


.MARINE...Persistent pattern across the coastal waters as high
pressure remains over the ne Pacific, with thermal low pres along
the south Oregon coast into nw Calif. This somewhat tight pressure
gradient will maintain northerly winds on the coastal waters, with
strongest winds in the afternoons/evenings to south of Cascade
Head. Will extend current small craft advisory for Cape Falcon to
Florence through Tue evening, as will maintain gusty winds at
times. May drop off from time to time, but think best to keep
broad-brushed advisory up.

Will extend Small Craft Advisory to include the coastal waters
between Cape Shoalwater to Cape Falcon, as gradient tightens a bit
more on Tue. Likely enough to support gusts 20 to 25 kt in
afternoon/evening. Winds will gradually ease Tue night into Wed,
as gradient weakens.

Seas mostly running 5 to 6 ft into tonight, but will see bit more
northwest swell arriving Mon. As such, seas 6 to 8 ft on the outer
waters across the northern inner waters, a bit less as move
southward along the west central Oregon coast. However, with the
gusty northerly winds, would expect locally higher choppy seas
on the waters at times, primarily afternoons/evenings./Rockey



PZ...Small Craft Advisory from noon Monday to 5 AM PDT Tuesday for
     Coastal waters from Cape Shoalwater WA to Cape Falcon OR
     out 60 NM.

     Small Craft Advisory until midnight PDT Tuesday night for
     Coastal waters from Cape Foulweather OR to Florence OR out
     10 NM.Coastal waters from Cape Foulweather OR to Florence
     OR from 10 to 60 NM.



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