FXUS66 KPQR 141703
AFDPQR

Area Forecast Discussion...Aviation Update
National Weather Service Portland OR
1002 AM PDT Sun Jul 14 2024

.SYNOPSIS...Above normal temperatures will persist for inland
portions of SW Washington and NW Oregon through next weekend,
though onshore flow should help to guard against more extreme
temperatures. Flow aloft will turn more southerly Tuesday,
potentially carrying moisture and instability northward from
California. This will lead to about a 10-20% chance of
thunderstorms Tuesday afternoon into Tuesday night, with the
best chance being east of Interstate 5.

&&

.SHORT TERM...Now through Tuesday...Little change is expected in the
weather today versus Saturday as stable but warm west-southwesterly
flow persists over the Pac NW. Strong upper level high pressure
remains anchored over the Four Corners region, with a weak cutoff low
festering off the coast of California. The air mass remains warmer
than normal, even for mid-July, with 500 mb heights remaining in the
mid to upper 580s dam and thus roughly 50-75 dam above normal. The
subsidence associated with the high pressure aloft is compressing the
marine layer, making it less effective at cooling the interior than
it usually is despite persistent onshore flow. Weak shortwave energy
dribbling through the Pac NW is deepening the marine layer a little,
latest Astoria PSL Profiler data suggest the marine layer was about
1500 ft deep as of 2 AM (up from 700-1000 ft Sat afternoon), and this
compares well with the satellite presentation of the marine layer
along the west slopes of the Coast Range on GOES-West 10.3-3.9um fog
product. As of 245 AM, stratus was knocking on the door of
Kelso/Longview, and it may briefly make it into north/east portions
of the PDX metro despite 06z HREF showing little to no chance of it
doing so. Even if clouds do make it into portions of the PDX metro,
it won't last long and will have almost no impact on temperatures
later in the day. Latest 00z GFS/EC ensembles show good agreement on
850 mb temps cooling a little today, from around +20 deg C Sat
afternoon to around +17 deg C this afternoon. This could provide a
few degrees of cooling today, especially to areas Salem northward.
"Cooling" is all relative though, as cooling a few degrees from Sat
still means highs in the upper 80s to mid 90s for the inland valleys
- which is still a good 10 degrees above mid-July climatological
averages.

Latest indications are that the marine layer will continue to deepen
slightly through this evening, potentially allowing for a more
intrusive push of stratus inland Monday morning. The 06z HREF does
show it this time, with 30-40% chances of stratus for the Vancouver
metro wrapping into the east side of Portland and southward to
Aurora. This marine influence, combined with continued robust onshore
flow, may be deep enough to have some impact on high inland, even
giving Salem a 20-30% chance of staying below 90 degrees Monday
afternoon. If so, it would be the first time Salem Airport remained
below 90 degrees since July 3 - ending an 11-day streak (assuming
today reaches 90 degrees, which is highly likely). The longest streak
of 90+ degree highs on record for Salem was 13 days, ending on August
10, 2017. Records have been kept in Salem since 1892.

If the marine influence fails to cool off Salem enough to keep them
below 90 degrees Monday, NBM suggests the sky is the limit as for how
long the streak may run, as each day has at least a 70% chance of
reaching 90 deg F all the way through Saturday July 20. If that were
to occur, the streak could go as long as 17 days or even longer.
Thirteen days into the month, Salem is +9.6 deg F above normal,
Portland is +8.2 deg F above normal, Eugene is +8.5 deg F above
normal, and even Astoria is +5.8 deg F above normal.

After the brief, relative "cooldown" today into Monday, the trend
reverses sharply on Tuesday as the upper low off California dislodges
and begins to lift northward. This will turn mid-level flow more
southerly and potentially even southeasterly, advecting some of the
hotter eastside air west of the Cascades. Unless debris from earlier
convection to our south leads to significant cloud cover Tuesday
afternoon, Tuesday has the potential to be the hottest day of the
week as 850 mb temps rise to +23 or +24 deg C. With full sunshine and
no marine influence, this could cause a few inland locations to flirt
with 100 deg F Tuesday (NBM now shows a 15-30% chance of this for the
Willamette Valley). If cloud cover is sufficient to hold down
temps, Tuesday afternoon, it will probably come with more humidity -
likely negating much benefit from the cooler temperatures.

A lot will depend on the timing of the disturbance lifting northward
from California - some of the more aggressive models suggest it may
lift fast enough northward to allow a southwesterly marine push to
cause temps to plateau in the lower 90s mid-Tuesday afternoon for
Eugene and Corvallis. Other, slower models show no such relief until
at least Wednesday. Another factor to consider will be convection
Tuesday afternoon... guidance continues to get more aggressive in the
potential for surface-based convection in the Cascades Tuesday
afternoon, evolving to elevated convection over most of our interior
Tuesday night. Again - timing is important here - and models
notoriously struggle with the timing of cutoff lows. But the way the
00z suite of models are depicting the situation, there is some
concern for the potential of numerous lightning strikes across
especially eastern portions of our CWA Tuesday night - and these
lightning strikes would be upon fuels that are much more prone to
ignition than they were just a couple weeks ago. For now, we handled
this with an area of slight chance of thunder developing over Lane
County Tuesday afternoon, progressing northward as elevated
convection and focusing mainly east of I-5 Tuesday night. This will
obviously need to be monitored closely, as fire weather headlines may
be necessary if guidance continues along this path.  Weagle

.LONG TERM...Tuesday night through Saturday...With plenty of cloud
cover expected after a hot, somewhat humid day, Tuesday night will
probably be unpleasantly warm north and east of Salem. Likely as a
result, the greater Portland/Vancouver metro area, western/central
Columbia Gorge, and Hood River Valley are all now showing Major
HeatRisk on Tuesday into Tuesday evening. Currently our high
temperatures are close to NBM guidance with highs Tuesday in the mid
to upper 90s for most of these areas. If this continues, we may need
to consider a Heat Advisory for these areas, but did not feel
comfortable issuing that just yet given the concerns mentioned above
regarding cloud cover.

Areas south of Salem, as well as the coastal valleys, have a better
chance of seeing substantial onshore flow Tuesday night into
Wednesday as the upper disturbance will likely deepen the marine
layer, potentially even pulling stratus inland behind it. If the
upper disturbance indeed lifts through western Oregon Tuesday night,
Wednesday, could be cooler than the lower 90s we are generally
showing for the interior lowlands Wednesday afternoon.

For those hoping for an end to the unusually warm weather this July,
looking at the long term forecast may be a bit of a disappointment as
GFS/EC ensembles show good agreement on 500 mb heights climbing back
toward 590 dam Friday and Saturday. If this occurs, it would again
compress the marine layer to the point where it can only effectively
cool the coast and coast range, and low clouds would likely be
limited to the coast. So, expect inland valleys to see highs
remaining around 90 degrees on average through next weekend, likely
with mild to warm nights in between.  Weagle

&&

.AVIATION...Marine stratus at the coast is in the process of
clearing, with mixed MVFR/IFR conditions. Stratus looks slower to
clear compared to yesterday morning, with the northern coast
(KAST) actually seeing 50-60% chance of mixed MVFR/IFR cigs
throughout daytime hours Sunday. At the southern and central coast
(KONP), there's around 70% confidence that clearing to VFR occurs
around 21z Sun, but the possibility exists that stratus never
fully clears and keep KONP MVFR/IFR throughout the day.

Winds remain fairly similar to yesterday, with NW flow slightly
increasing Sunday afternoon around 22z Sun. Winds at the coast can
expect gusts up to 20 kt, while inland terminals will see
sustained winds up to 10 kt. All inland terminals remain VFR with
clear skies throughout the period.

PDX AND APPROACHES...Clear skies VFR throughout the TAF period.
Sustained winds up to 10 kt Sunday afternoon (22z Sun - 06z Mon),
but otherwise mild conditions expected. /JL

&&

.MARINE...High pressure will maintain northerly winds across the
waters for much of the next week. Winds will generally be
strongest off the central coast of Oregon and lightest off the
mouth of the Columbia River each day. Winds will typically peak
each day in the late afternoon and evening hours, with gusts at
times just barely meeting Small Craft Advisory criteria at 20-25
kt.

Probabilities of 20 kt winds or greater do decrease substantially
(to less than 20%) across the waters off even the central coast
of Oregon towards next Tuesday and Wednesday. In the meantime,
seas will primarily be a hybrid of fresh swell/wind-driven waves
through the weekend.
-JH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

www.weather.gov/portland

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