772
FXUS66 KPQR 090319 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
819 PM PDT Wed May 8 2024

.SYNOPSIS...A stout ridge of high pressure continues to build
across the region the latter half of the week resulting in a
prolonged period of dry weather and rapidly warming temperatures
day to day. It still appears near record breaking heat is in
store Friday into Saturday  daytime highs climb in the mid 80s
to near 90 across the inland valleys. Cooler onshore flow
returns Saturday night into Sunday resulting in slightly cooler
temperatures for the early to middle portion of next week albeit
still near to slightly above seasonal norms.

&&

.SHORT TERM...Tonight through Saturday...Visible satellite
imagery this afternoon shows little in the way of cloud-cover
thanks to the influence of a ridge of high pressure building
over the far eastern Pacific. Tonight and Thursday night well
still need to keep our eye on pockets of fog developing near
sunrise in some of the more sheltered locations across region
particularly the central and south Willamette Valley due to
light winds, clear skies, and lingering surface moisture however
impacts should be rather negligible and localized. Going forward
through Thursday and Friday the ridge will continue to amplify,
tilting eastward into British Columbia and increasing offshore
flow over the Pacific Northwest. Temperatures rapidly warm as a
result with excellent agreement between deterministic and
ensemble guidance into the weekend. Given the development of
low-level offshore flow and surface thermal trough building
overhead as well, confidence is very high(90-99%) in afternoon
temperatures reaching into the upper 70s to low 80s across the
inland valleys Thursday followed by another 6-10 degree jump
into the mid/upper 80s to near 90 Friday. Temperatures across
the Willamette Valley, SW Washington, and other inland valleys
appear very similar on Saturday compared to the day prior
(Friday) - both days present a 60-80% chance to break 90
degrees in the Portland/Vancouver Metro according to the NBM.

The greatest uncertainty in the temperature forecast lies along
the coast where low-level (925-850mb) offshore winds aided by
down-sloping off the coast range will attempt to usurp any weak
marine/sea-breeze influence intent on keeping afternoon high
temperatures suppressed. Will need offshore surface winds at the
coast for most of the day for this to occur, and the placement
of the aforementioned thermal trough is still marginal for
inland-like temperatures to extend this far westward. Should the
axis thermal trough trend slight more offshore (current set- up
hugs the coastline) temperatures would likely jump into the
80-85 range for many of the beaches south of Cape Falcon on
Friday. Regardless of the outcome, the progression the thermal
trough eastward and increasing westerly flow at the coast will
almost certainly lead to cooling on Saturday when compared to
Friday.

These unseasonably warm temperatures will no doubt cause some
people to flock to the rivers, lakes, and ocean beaches of SW
Washington and NW Oregon. It is important to remember that
rivers and lakes remain dangerously cold with water temperatures
mainly in the 40s. Such temperatures can easily cause cold
water shock for those without proper cold water gear. The bright
sun and warm temperatures can make the cold water look
refreshing, but the consequences of jumping in could be deadly.
Be sure to bring a life vest and be extremely cautious around
area rivers, especially given the swift currents also in place!
-Schuldt


.LONG TERM...Sunday through Wednesday...More widespread cooling
is expected on Sunday as the ridge of high pressure withers in
response to a weak upper-level shortwave pressing eastward
towards the coast. The axis of the near surface thermal trough
also shifts east of the Cascades into the Columbia Basin -
widespread westerly onshore flow returns. The marine layer will
likely remain too shallow for much in the way of morning
cloudiness inland through Sunday, but the upper ridge may weaken
enough for some low clouds to push into the inland valleys for
a few hours Monday morning. Cannot rule out patchy light drizzle
at the coast Sunday night into Monday morning as well,
especially given the weak upper- level shortwave progressing
overhead providing some added support.

Beyond this point guidance is a little more uncertain resolving
the large scale upper-level pattern. This is largely derived
from the development of a second ridge of high pressure over the
eastern Pacific although the exact longitudinal placement and
amplification will heavily modulate temperatures by Tuesday and
Wednesday. Around 40% of ensemble members favor a solution which
brings a more amplified ridge overhead by the middle of the
week allowing temperatures to climb back into at least the
upper 70s to low 80s while 45% of members shunt the ridge
further west to varying degrees - mostly dry with highs in the
60s to near 70 if this solution occurs. The remaining 15% dig a
trough over WA/OR spelling the return of showers and cooler
conditions. So the main takeaway is mostly dry and near to above
normal temperatures remain favored(~85%) int the middle next
week but we cant completely rule out the off-chance(~15%) of a
wetter pattern as of now. At least there will be plenty of
sunshine and warm temperatures to enjoy before we make it to
that juncture.-Schuldt


&&

.AVIATION...Dry, northerly flow with an upper level ridge of high
pressure over the airspace. This is resulting widespread VFR
under mostly clear skies. North to northwest winds with gusts to
around 20-25 kt through around 15Z Thursday. Light offshore flow
develops overnight with VFR continuing through Thursday morning.

PDX AND APPROACHES...VFR under mostly clear skies. Northwest
winds with gusts to around 15 kt through around 06Z Thursday.
Winds ease to around 5 kt after 08Z Thursday. /42

&&

.MARINE...Strong high pressure is currently centered about 400
miles offshore while a thermally induced inverted trough of low
pressure is hugging the coast along northern CA into southern OR.
The tightened pressure gradients across the coastal waters will
produce breezy northerly winds with gusts up to 30 kt through
tonight, strongest south of Tillamook Bay. The northerlies ease
somewhat on Thursday, but can expect gusts to 25 kt across much of
the coastal waters south of Cape Falcon to return by Thu afternoon
and into the evening. Winds ease further by Friday as high
pressure weakens and shifts westward and the thermal trough
extends just off the Oregon coast into SW Washington. This will
also allow for a more offshore northeasterly wind Friday morning.
Then, winds are expected to return N/NW around 10-20 kt through
the remainder of the weekend. Seas will likely hover around 7 to
9 feet through the end of the week, and then to around 5 to 6 ft
over the weekend. /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

     Small Craft Advisory until 5 AM PDT Thursday for PZZ251-271.

     Small Craft Advisory until 11 PM PDT Thursday for PZZ252-253.

     Small Craft Advisory until 5 AM PDT Friday for PZZ272-273.
&&

$$

www.weather.gov/portland

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