676
FXUS66 KPQR 041646 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
945 AM PDT Tue Jun 4 2024

Updated Aviation and Marine discussions

.SYNOPSIS...Subtropical moisture continues to stream across the
Pacific and into the Pac NW today, guided along a quasi-stationary
frontal zone by unseasonably strong Pacific jet stream. Inland
valleys will mostly just see occasional light rain, mainly north of
Salem. Coast and mountain locations will see significantly more rain
than the inland valleys, especially in SW Washington. An upper level
ridge will build northward tonight into Wednesday, bringing an end to
the rain. Cool temperatures today will rebound to seasonal normals
Wednesday, then climb several degrees above normal by Friday.

&&

.SHORT TERM...Today through Thursday...Latest GOES-West satellite
imagery clearly shows an atmospheric river of moisture making
landfall into WA and northern OR, travelling along a quasi-stationary
frontal zone draped across the region. Analysis of infrared imagery
seems to indicate a developing low off the WA coast, which is likely
contributing to the very gusty winds along the WA and extreme
northern OR coast. An earlier wind gust to 59 mph was recorded at
Clatsop Spit, and gusts in the 40-50 mph range have occurred at both
Astoria and Hoquiam Airports within the past couple of hours. These
stronger winds are likely being aided by a coastal jet, which is
evident on KLGX imagery in the narrow ribbon of stronger, more
southerly winds extending from the surface up to around 1000 ft.
These coastal jet winds will likely peak by 6-7 AM as the low moves
onshore, but rapidly building high pressure from the SW will keep it
breezy at times with gusts 25-35 mph possible throughout the day
anywhere in SW Washington and NW Oregon. Guidance suggests the winds
will be stronger during the morning for inland areas, but daytime
mixing and persistent SW flow above the surface should keep it
blustery into the afternoon.

Our foray into autumn weather comes to an end tonight into Wednesday
as a strong upper level ridge of high pressure begins to bulge
northward from California. The resulting subsidence will bring an end
to rain chances, first for the lowlands tonight but eventually the
higher terrain on Wednesday. Some clearing is possible Wednesday
afternoon, and with the air mass warming up, temps should climb back
to normal or slightly above normal Wednesday afternoon. The warming
trend will continue into Thursday, with most GEFS and EC ensemble
members warming into the mid teens Celsius at 850 mb. With near full
sunshine likely Thursday, this should allow at least some of our
inland valleys climb into the 80s Thursday afternoon. Thermal low
pressure strengthening over SW Oregon will likely turn low-level flow
more N-NE Thursday morning, so it is possible Thursday will be sunny
along the coast with highs pushing into the 70s. Onshore flow returns
later Thursday afternoon, possibly with some coastal stratus.  Weagle


.LONG TERM...Friday through Monday...The forecast through the weekend
can probably be best described as the opposite of what we`ve been
seeing in the Pac NW in recent days. Strong upper level ridging
continues to expand northward Friday, continuing to heat up the air
mass over Oregon and southern WA. 00z GEFS/EPS members highly suggest
850 mb temps will peak Friday afternoon, somewhere between +15 and
+20 deg C. Onshore flow and high soil moisture content from recent
rains will likely make it hard for temperatures to climb much higher
than 90 degrees, but that will probably come at the expense of higher
humidity along with the very warm conditions inland.

While earlier guidance had suggested a prolonged upper level ridge
affecting the region, latest runs have tended to tone down the
amplitude of the ridge while shifting the ridge axis eastward. This
will serve to maintain the strongest part of thermal low pressure
east of the Cascades, pulling the moderating influence of the Pacific
Ocean as far east as the Cascades. This trend is beginning to show in
NBM probabilistic guidance, where probabilities of temps reaching the
90s in the Willamette Valley fall off dramatically beginning
Saturday. While these probs were around 50% for Saturday based on
models run Sunday night, these chances are now down to 10-20% for
most of the Willamette Valley.

Confidence is high that the upper ridge axis will remain east of the
Cascades into early next week, which will allow some degree of
onshore flow to continue. The degree of cooling provided by this
onshore flow (largely determined by the depth of the marine layer),
remains uncertain with a large amount of variability between models
in 500 mb heights. Lower heights would contribute to a deeper marine
layer and cooler temps, while higher heights would compress the
marine layer and make it less effective in cooling off inland areas.
00z WPC cluster analyses indicate high likelihood that 500 mb heights
will remain above normal into next week, so the pattern seems to lend
to near normal coastal temps and temps a few degrees above normal
inland, but nothing dangerously hot.

Flow aloft also turns more southerly over the weekend as jet stream
energy from the Pacific buckles while approaching the upper ridge to
our east. Depending on the amount of subtropical moisture available,
this may open the door for a few showers and thunderstorms in the
Cascades by the weekend.  Weagle

&&

.AVIATION...A frontal system continues to push across the region
today with strong westerly flow aloft. Light rain will gradually
dissipate through the day. Expect low MVFR to IFR conditions along
the coast to gradually lift this afternoon, becoming a mix of high
end MVFR to VFR by 06Z Wednesday. Guidance continues to suggest
there is a 40-80% chance of MVFR through this afternoon (best
chances between 18-22Z), with predominately VFR becoming more
likely after 00Z Wednesday. Though, with the slowly moving front,
MVFR CIGS are more likely to hang on longer through the southern
and possibly central Willamette Valley, including KEUG where probs
increase to 60-80% after 00Z and linger there through 15Z
Wednesday. Southerly winds continue to gust this morning to
around 25-35 kt along the coast, but are expected to quickly ease
becoming southwest once the front moves onshore by 22-23Z this
afternoon. Expect breezy south to southwest winds with gusts to
20-25 kt continue through this afternoon across the Willamette
Valley.

PDX AND APPROACHES...VFR as of 16Z this morning, but chances for
MVFR increase to around 70-80% between 18-22Z Tuesday. VFR becomes
more likely again after 03Z Wednesday. Breezy southwest winds
expected with gusts up to 20-25 kt through this afternoon. Then,
once the front pushes through, winds are expected to ease below 10
kt becoming more west to northwest. /DH


&&

.MARINE...A frontal system will continue to slowly push onshore
today. As of 9 AM Tuesday, southerly winds continue near the coast
with gusts of 25-35 kt, but are expected to quickly ease as the
front moves onshore later this morning. Southwest winds around
15-20 kt are expected by this afternoon across most of the coastal
waters, then gradually turning northwest and easing further
overnight. Will maintain the Small Craft Advisory as seas are
expected to remain elevated through Wednesday night.

Seas remain steep and choppy at around 10 to 12 feet through
tonight. An incoming northwesterly swell will likely cause seas
to build to around 12 to 14 feet late tonight through Wednesday.

High pressure builds midweek for more settled conditions. Expect
a summertime pattern with high pressure offshore and a thermal
trough along the coast, bringing northerly winds gusting to 25 kt
at times through the end of the week. Seas around 8 to 10 ft on
Thursday likely to subside to around 6 ft on Friday. /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT Wednesday for PZZ210-
     251>253-271>273.
&&

$$

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland