367
FXUS66 KPQR 070456
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
956 PM PDT Sat Jul 6 2024

.UPDATED AVIATION DISCUSSION...

.SYNOPSIS... An ongoing heatwave will continue to impact
locations away from the coast with record breaking temperatures
through Tuesday due to strong high pressure aloft. Temperatures
will trend cooler Wednesday into Thursday as onshore flow
strengthens, bringing much needed relief to the area (especially
during the overnight hours). A trickle of onshore flow may
bring some cooling into the coastal valleys Sunday, but inland
areas and elevations above 1000 ft will remain very hot. No rain
is in sight through next weekend.

&&

.DISCUSSION...Saturday night through Friday night...Minimal changes
to the deterministic forecast this morning. NW Oregon and SW
Washington remain within the grip of a prolonged and dangerous heat
wave.

Confidence is high the ongoing heatwave will continue impacting
inland areas with triple digit high temperatures and poor overnight
relief through Tuesday evening as a thermal trough deepens along and
west of the Cascade crest. The deterministic NBM has remained quite
consistent for high temps through Tuesday, suggesting highs will most
likely top out around 100-105 degrees and low temps between 65-70
degrees across the Willamette Valley, Cowlitz Valley,
Portland/Vancouver metro and Columbia River Gorge. The latest NBM
probabilities have changed a bit in some locations, but not by very
much (see table near the bottom of this discussion for the latest
probabilities). With the thermal trough overhead, will not see all
that much in way of winds. Despite the lack of wind, humidity values
are way down at 10-20% for most inland locations each afternoon.
Although it does not feel humid outside, the hot and dry conditions
can easily result in dehydration for those who are not drinking
enough water. Everyone should do their best to stay hydrated and
avoid strenuous and/or prolonged outdoor activities to avoid heat
exhaustion or heat stroke. This will be especially true between
11am-7pm when temperatures will be hottest. Got animals? Consider if
they have adequate shade and water, and perhaps consider taking them
out earlier in the day or in the evening when temperatures will be a
bit cooler. Keep in mind that their paws can easily burn on hot
surfaces like concrete and asphalt; another reason to take them out
during the cooler morning hours. As always, never leave people or
animals inside a hot car. Parking in the shade does not help enough
during periods of extreme temperatures, nor does cracking your
windows open. Anyone with outdoor plants/gardens will need to water
frequently (ideally in the evening and/or early morning). Plants that
are susceptible to sunburn should be shaded if possible.

In addition to the hot afternoon temperatures, it still appears there
will be minimal overnight relief as low temps will be running quite
warm (especially in Portland, Salem, the Columbia River Gorge and the
mid slopes of the Cascades). Keep in mind it will take quite some
time for temperatures to fall each evening. Many lowlands areas may
not see temperatures drop back under 90 until 7-8 pm (especially in
urban areas). Overnight lows will likely fall back to the upper 50s
to middle 60s for outlying rural area, however urban areas will
struggle to dip much below 70 degrees. This is especially true Monday
night when the probability for overnight lows above 70 degrees peak
at 10-25%. The mid slopes of the Cascades will remain warm at night
as well due to a temperature inversion, with some locations
potentially seeing lows in the mid to upper 70s (10-25% chance).

Will see a slight uptick of onshore flow Saturday night, enough to
drop the coast back to more pleasant temperatures for Sunday. This
means this heatwave event has essentially come to and end for the
coast, as high temps will likely top out in the 70s Sunday through
Tuesday. While that is still warmer than normal for the coast, this
level of heat only warrants a minor HeatRisk. Meanwhile, inland
valleys remain under a major to borderline extreme HeatRisk. As such,
an Excessive Heat Warning remains in effect through Tuesday for
locations away from the coast, aside from the Cascades which is under
a Heat Advisory.

For the Willamette Valley, the record number of days in a row with
highs temps of 100 degrees of warmer is 5 days, set in mid-July 1941
at Portland airport. Many areas in the Willamette Valley/Clark County
have seen 4 days in row a few times, such as back in August 2023, or
2015 or in 1981. For this heatwave, it looks like 4 days of 100+ deg
heat is a good bet at PDX, but will see if the record 5 days is
reached.

Here are the odds of reaching 100+/105+ deg at select cities, based
on the 19z iteration of the NBM on July 6th via the 1D Viewer:

Sun     Mon Tue      Wed
       July 7    July 8July 9     July 10
      100  105   100105    100  105     100  105
  ========================================================
Kelso      50%   1%   60%20%45%  20%     0%   0%
Portland*     75%  20%   80%40%80%  45%     0%   0%
Salem      99%  65%   95%70%95%  75%     0%   0%
Eugene      90%  25%   80%45%75%  25%     0%   0%
Hood River    75%   5%   90%40%99%  50%    10%   0%

The % of reaching 110 or higher is <5% for all areas, except on
Tuesday when there is a 5-20% chance across the Willamette Valley
(best chance in Salem, second best chance in Portland).

*Portland is for Greater Portland/Vancouver metro area.

The latest model guidance continues to suggest onshore flow will
begin to increase Tuesday night into Wednesday as the thermal trough
shifts east of the Cascades. This will bring westerly winds to the
west side of the Cascades, with a modest cooldown for the interior
for Wednesday. Overall, temperatures on Wednesday look to be in the
upper 80s to middle 90s, but even cooler temperatures for Thursday
and Friday with highs likely in the mid to upper 80s. Overnight lows
will improve as well during that time, most likely falling into the
mid to upper 50s (70-90% chance). -TK/Rockey/Weagle

&&

.AVIATION...High pressure will maintain clear skies and VFR
conditions for inland sites through the period with hot daytime
temperatures. As a result, expect the potential for high density
altitude effects on takeoffs during peaking heating in the
afternoon hours. Air mass along the coast cools later tonight into
Sunday morning, with pockets of IFR stratus and fog forming just
onshore before clearing later in the morning. Confidence in the
exact placement of any coast low clouds and timing of
development/clearing is only low to moderate at this time.

PDX AND APPROACHES...High pressure maintains VFR conditions
through the period. -Schuldt

&&

.MARINE...
Not much in way of change. Thermal low pressure just
onshore extending southward along much of the coast. Meanwhile,
high pressure remains anchored well offshore. This will maintain
northerly winds on the waters into early next week. Gradients
tight enough to pop gusts to near 20 kt in afternoons/evenings,
but that will be generally south of Cascade Head today and again
Sunday. Seas mostly a mix of wave fetches: one at 1 to 2 ft from
the southwest, with the other from the west-northwest at 2 to 4
ft. As such, overall combined seas stay in the 3 to 4 ft range
into early next week.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning until 10 PM PDT Tuesday for ORZ104>125.
     Heat Advisory until 10 PM PDT Tuesday for ORZ126>128.
WA...Excessive Heat Warning until 10 PM PDT Tuesday for WAZ202>210.
     Heat Advisory until 10 PM PDT Tuesday for WAZ211.
PZ...None.
&&

$$

www.weather.gov/portland

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