382
FXUS66 KPQR 070351 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
850 PM PDT Thu Jun 6 2024

Updated Aviation and Marine Discussions

.SYNOPSIS...Going into the weekend high pressure likely
maintains mostly dry conditions and above normal temperatures
although once we get beyond Friday high temperatures will begin
a decline going forward, albeit very gradually Sunday onward.
Late Saturday into Sunday expect increasing cloud cover due to a
weak upper-level trough, but little to no precipitation expected
outside of shower activity near the Cascade crests and the
potential for morning drizzle along the coast. Back to weak
ridging/zonal flow aloft Monday through Wednesday  no
appreciable weather impacts. Some guidance shows a breakdown in
the upper-level pattern via a upper trough pushing into the
Pacific Northwest from the Gulf of Alaska around Thursday of
next week ushering in chances (15-40%) for light precipitation
however exact timing/amounts at this point are unclear.


.SHORT TERM...Today through Sunday...Expect high pressure to
persist over the Pacific Northwest through the end of the work
week and most of Saturday maintaining dry conditions and warm
temperatures. The axis of the upper-level ridge shifts overhead
on Friday, subsequently at the same time a subtle shortwave
traverses overhead(well get to that in a minute), but the
primary impact of this overall pattern will be afternoon high
temperatures 15 to 20 degrees above normal for the inland
valleys away from the marine influence from the coast. The
latest NBM guidance suggests a high degree of confidence
(70-90%) in temperatures meeting or exceeding at least 85
degrees across the Willamette Valley, SW Washington, and in the
Cascade valleys come Friday afternoon. However given a slight
offshore component to the surface-850mb flow and clear skies
thinking 90 degrees is within the realm of possibility for the
Portland/Vancouver metro and base of the Cascade foothills even
if the NBM probabilities to meet/exceed 90 are only 30-50%.
These locations will have a moderate heat risk - this level of
heat affects most individuals sensitive to heat, especially
those without effective cooling and/or adequate hydration. Keep
this in mind if you plan on spending any extended period of time
outdoors.

Another feature worth watching on Friday, specifically late in
the day, is a weak/subtle upper-level shortwave traversing into
Oregon accompanied by a plume of mid-level moisture situated
around 700-600mb. With ample daytime heating just before the
arrival of this feature and models like the NAM/GFS showing
around 300-500j/kg of MUCAPE in an elevated layer between
700-300mb the environment is marginal for the development of
isolate mid-level based convection along the crests of the
Cascades along far eastern Lane County late Friday
afternoon/evening. The latest HREF does show a couple members
initiating weak thunderstorms in this region of mid-level
moisture/insatiably so have added a slight chance(10-15%) for
thunderstorms along the Lane/Deschutes county line, although
chances for isolated convection appear more favorable further SE
where the mid-level moisture layer is more robust. All that
being said, both the HRRR, 4KNAM, and UW-WRF are fairly bearish
within the greater CAM ensemble space during this period along
the Cascades into central Oregon so confidence in the set-up is
rather low likely owing to a rather deep dry layer just above
the moisture at 700-600mb working to entrain dry air into rising
parcels - this would inhibit the formation of any
thunderstorms. All in all, dont be taken by complete surprised
if an isolated T-storm does indeed develop along the
Lane/Deschutes county line Friday but the window for any
activity will be rather brief (4-8pm), if anything actually does
materialize.

Friday night, the upper level ridge begins to progress eastward
as a weaken upper-level trough approaches the Pacific Northwest.
This will bring more southwesterly flow aloft as well as
increasing mid to high level cloud cover Saturday. Since our air
mass will be so dry when this shortwave moves in, it`s unlikely
that we`ll see much precipitation outside of a 15-30% chance for
showers along the Cascades late Saturday night through Sunday.
The added westerly flow and cloud cover will help to lower
temperatures through the weekend with high temperatures likely
in the upper 70s to low 80s for the inland Valleys on Saturday,
dropping into the mid 70s to near 80 on Sunday - still pleasant
overall. Low temperatures continue to bottom out in the 50s
providing some overnight cooling. -Schuldt

.LONG TERM...Sunday Night through Thursday Going forward into
early next week most WPC ensemble clusters are in general
agreement of maintaining low amplitude high pressure with above-
normal 500 mb heights over the Pacific Northwest through
Wednesday. However, the clusters still differ on the precise
magnitude and placement of the ridging, more apparent beginning
on Wednesday when ensemble guidance shows an upper trough near
the Gulf of Alaska beginning to show signs of progressing
southward towards British Columbia and potentially the Pacific
Northwest. Depending on how far south this trough ends up at
this point, this would influence the strength of high pressure
over us and thus how warm we end up getting around the middle of
next week. Come Thursday nearly 35-40% of the total ensemble
members begin to bring the aforementioned broad upper-level
through into the region thus increasing chances for
precipitation should this scenario pan out. The remaining 60-65%
of ensemble keep the influence of the low amplitude ridge
overhead to varying degrees, shunting the trough to our north.
Generally speaking, the pattern favors a continuation of above
normal temperatures through the extended, but with less
confidence on where high temperatures will ultimately land
around the middle of next week. -Schuldt/Alvis

&&

.AVIATION...High pressure will remain in control across the
region through the weekend. This will result in warm and dry
conditions with widespread VFR under primarily clear skies.
North/northwest winds, generally 5-10 kt inland and up to 15
kt along the coast, with wind gusts up to 25 kt along the coast
and gusts up to 20 kt within the Willamette Valley. Inland winds
will become light and variable after 06Z Friday. Coastal winds
will remain elevated through the overnight hours, but gusts
expected to fall below 15 kt around 15Z Friday. Gusty surface
conditions return across the airspace around 20Z Friday with gusts
along the coast up to 20 kt and gusts inland up to 15 kt.

PDX AND APPROACHES...VFR with generally clear skies. Northerly
winds with gusts up to 20 kt through 06Z Friday. Afterwards,
winds become light and variable. /42

&&

.MARINE...High pressure over the region will lead to clear skies
and fairly persistent north/northwest winds through the weekend.
Gusts up to 25 knots across all waters through early Friday
morning. Conditions will slowly subside from north to south
through Friday morning. Could see some isolated gusts up to 25 kt
within zones PZZ272, PZZ252, PZZ273 and PZZ253 through Friday
afternoon. Seas remain steep around 7 to 9 ft at 10-12 seconds.
Therefore, have adjusted the current Small Craft Advisories to
reflect the newest data from the forecast models.

Conditions will begin to ease on Saturday as a very weak front
nears the waters. This front appears to have limited impact, but
cannot rule out some isolated gustier conditions. Seas will lower
to around 5 to 7 ft at 12 seconds. /42-Batz/Muessle


&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 4 AM to 8 AM PDT Friday for PZZ210.

     Small Craft Advisory until 1 AM PDT Friday for PZZ251-271.

     Small Craft Advisory until 6 AM PDT Friday for PZZ252-253-272-
     273.
&&


$$

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