340
FXUS66 KPQR 010507 AAB
AFDPQR

Area Forecast Discussion...Update
National Weather Service Portland OR
1007 PM PDT Sun Jun 30 2024

.UPDATE...Made some quick updates to the forecast this evening to
accommodate some dense fog that has developed along Oregon`s Central
Coast and the adjacent waters. The fog is likely so dense due to
relatively high-dewpoint air moving over the cooler waters, with the
fog being pushed onto the coast by light onshore flow. The fog will
probably be slow to lift Monday morning, but 00z HREF shows gradually
decreasing probs of dense fog after sunrise. Aviation section was
recently updated below as well.  Weagle

&&

.SYNOPSIS...Onshore flow will maintain near to slightly above average
temperatures through midweek. Building high pressure over the eastern
Pacific and Pacific Northwest will bring a 60-70% chance for the
hottest temperatures of the Summer so far by the end of the work
week.


&&


.SHORT TERM...Tonight through Wednesday...In the short term, visible
satellite imagery and radar reveal a few very light showers over
mainly the north Oregon Coast Range and Willapa Hills. The convection
appears to be capped well below 700mb, which is limiting rainfall
generation and resulting in mostly shallow cumulus clouds forming
over the region. Meanwhile, visible satellite imagery reveals a weak
surface trough off the Oregon coast that models agree will shift
towards the coast overnight. Some HREF members and global ensemble
members suggest light showers will return the coast late tonight into
Monday morning. Any rainfall amounts appear most likely
to be a couple hundredths of an inch or less. Another round of areas
of fog will once again develop over the waters and along portions of
the coast.

Otherwise, an upper level shortwave trough will slowly shift eastward
away from the Pacific Northwest early this week. This process will
result in only a very gradual warming trend through midweek with
temperatures remaining near to slightly above average during this
period.  /Neuman


.LONG TERM...Thursday through Sunday...The global ensembles appear to
be converging on a solution that results in high pressure shifting
over the Pacific Northwest late in the work week into next weekend.
However, there are still some differences in the magnitude of the
ridge and the timing of the ridge. The net result is that there
still remains a fairly wide range of possibilities for temperatures,
particularly on any given day with the main uncertainty revolving
around which day will be the hottest, and perhaps more importantly,
the duration of the heat.

The most likely scenario (generally a 60-70% probability) is that we
heat up enough to experience our hottest temperatures (at least the
low to mid 90s) of the Summer so far by Friday or Saturday. However,
the probabilities for 100F temperatures are not insignificant and
currently lie around the 40-50% range per the NBM for Friday and
Saturday in the Willamette Valley. Note there is a small subset of
the global ensembles that produce 100s on Friday and Saturday that
keep us locked in a pattern that keeps 100s around well into the
following week for a long duration heatwave. At this point, this
scenario appears to have a low probability (~10-20%) of coming to
fruition, but it`s not certainly not a zero percent chance of
happening either.

On the opposite side of the spectrum, there is a small subset of the
ensemble guidance (~10-20%) that suggests ridging will be short
lived and/or low amplitude enough to make 90F difficult to achieve
on any given day between Thursday and Saturday. Overall, NBM
temperature and RH values appear completely reasonable given the
uncertainty in exactly how hot the area will get and the magnitude
of the ridge (and height of the resulting subsidence inversion) so
stuck with the deterministic NBM throughout the extended. /Neuman


&&


.AVIATION...Increasing northwest flow aloft while marine stratus
developing along the coast this evening expected to fill in
overnight with IFR to LIFR cigs persisting through Monday morning.
Chances for VFR increase to around 70-80% after 20Z Monday for
coastal terminals. Expect low VFR to MVFR cigs to form inland
overnight with a 30-50% chance of MVFR between 12-18Z Monday.
Onshore flow increases again by Monday afternoon with breezy
northwest winds expected.

PDX AND APPROACHES...Predominately VFR expected through the
period. Guidance suggests there is a 40-50% chance for MVFR cigs
2000-3000 ft between 12-18Z Monday morning at PDX, higher chances
(60-70%) at KTTD. Northwest winds around 5-7 kt becoming light
overnight, then increasing again Monday afternoon. /DH

&&

.MARINE...Weak high pressure over the northeast Pacific with lower
surface pressure over California and the Great Basin will more or
less continue through the week. A weak area of surface low
pressure will pass over the area through tonight, supporting
initially southwest winds before turning to the west in its wake.
Otherwise, expect north to northwest winds across the waters as
high pressure strengthens toward the middle of next week, with the
strongest winds generally off the central coast of Oregon and
lighter winds farther north. Winds will generally peak in the
afternoon and evening hours each day. For now have issued a Small
Craft Advisory for the central zones, but may need to expand
further north. Because as a thermal low develops along the
northern California/southwest Oregon coast on Tuesday and
strengthening/spreading north into Wednesday and thereafter. As a
result will see an increase the pressure gradient along the coast
and over the waters with a >90% chance that northerly wind gusts
of 20-30 kt spread northward across the waters by mid week. This
will in return develop steep wind driven seas of 5-8 ft with a
dominant period of 7-8 seconds by late Tuesday or Wednesday.
/mh -Batz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Dense Fog Advisory until 9 AM PDT Monday for ORZ103.
WA...None.
PZ...Dense Fog Advisory until 9 AM PDT Monday for PZZ253-273.
     Small Craft Advisory from 5 PM Monday to 5 AM PDT Wednesday
     for PZZ253-273.

&&


$$

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