745
FXUS66 KPQR 041101
AFDPQR

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

.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 warm front will push through the region early today
with a cold front settling over northwest Oregon tonight as it
dissipates. VFR prevailing as of 09Z with some MVFR at the coast.
Forecast for IFR to develop at the coast by 12Z as rain increases.
IFR chances decrease at the north coast about 16Z Tue with VFR
chances towards 00Z Wed. The central coast (KONP area) have high
chances >80% til about 00Z Wed. A lot has to do with where the
cold front ends up stalling. MVFR chances start ramping up for
inland areas by 12Z Tue with 70-90% chance around 18Z Tue. Then
trending to VFR after 00Z Wed, but KEUG may remain MVFR into the
evening.

Southerly winds gusting 30 to 40 kt along the coast with strongest
winds near KAST. Winds ease quickly once the front moves ashore
12-14Z Tue. Inland areas will see southerly wind gusts 15-25 kt
around 12Z Tue, then gradually ease through the afternoon.

PDX AND APPROACHES...MVFR chances increasing early this morning
with around 80-90% chance by 17Z Tue, the VFR likely towards 00Z
Wed. Southerly wind pickup to 8 to 12 kt with gusts near 20 kt
around 12Z Tue and continue at times through the afternoon before
easing.

&&

.MARINE...Frontal system moving across the waters bringing gusts
to 35 kt for most of the waters. A bit of a coastal jet developed
along the north Oregon coast. Clatsop Spit reporting gust to 37 kt
with a peak wind of 51 kt. Astoria airport had a gust to 39 kt at
1 am. Winds are expected to ease around 5-6 am as the front moves
through.

Gale Warning continues for coastal waters north of Cape Foulweather,
including the Columbia River Bar until 8 AM, the transition to a
Small Craft Advisory into Wednesday. Small Craft Advisories
continue for the zones south of Cape Foulweather through
Wednesday. Seas remain steep and choppy at around 10 to 12 feet
through Wednesday. An incoming northwesterly swell will likely
cause seas to build to around 12 to 14 feet Tuesday night 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 /mh

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Gale Warning until 8 AM PDT this morning for PZZ210-251-252-271-
     272.

     Small Craft Advisory from 8 AM this morning to 11 PM PDT
     Wednesday for PZZ210-251-252-271-272.

     Small Craft Advisory until 11 PM PDT Wednesday for PZZ253-273.
&&

$$

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