568
FXUS66 KPQR 082201
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
300 PM PDT Mon Jul 8 2024

.SYNOPSIS...This past weekend was hot, and it`s going to get hotter.
The one exception to this is for those lucky enough to be along the
coast, where sea breezes will keep it cooler. Otherwise, dangerous
heat will continue through Tuesday with more triple digit heat.
Temperatures are expected to peak for inland areas Tuesday, when
highs could reach 105 degrees. A strong onshore push will bring some
relief for Wednesday, keeping temps more moderate through the
weekend. That said, we are still expecting it to be warmer than
normal for the next 7-10 days, but the onshore flow should take Pac
NW temps out of record territory beginning Wednesday.

&&

.DISCUSSION...Monday night through Sunday night...Dangerously hot
weather continues for all but the coast through Tuesday, with day
after day of record breaking temperatures for much of the interior
lowlands.

KEY POINTS:

1. Record or near-record heat will persist inland through Tuesday.

2. High temperatures will likely reach 100-105 degrees over
the Willamette and Hood River Valleys on Tuesday, similar to what has
been observed thus far on Monday.

3. Tonight will be even slower to cool off in urban areas than the
last several nights. Strengthening onshore flow will bring some
relief to all locations Tuesday night into Wednesday, however temps
will still be running above normal.

4. The prolonged and compounding nature of this heat wave will make
it increasingly hard for people, pets, and plants to cope with the
heat. This will especially be the case for those with medical
conditions that make them sensitive to heat. A major HeatRisk
continues over the interior lowlands.

5. Coastal areas will remain cooler, with highs generally in the 70s
on Tuesday. Trending even cooler Wednesday onward.

High temperatures finally reached 100 degrees at PDX on Sunday, July
7th after falling one degree short on July 5-6. Although this heat
event won`t break the record for the highest number of consecutive
days with max temps of 100 degrees or warmer at PDX, this record
likely will be broken for Salem and Eugene when this heat wave is
over with come Wednesday, as these two locations have observed high
temps above 100 degrees from July 5-7 and are extremely likely to
warm to 100 degrees or warmer on July 8-9 as well (85-90% chance).
Despite PDX not breaking this particular record, this heat event will
almost certainly tie the heat wave events that occurred in July 1941
and August 1981 for the most consecutive days at or above 99 degrees
at Portland Airport with five days. So this heat wave still takes its
place amongst the most significant heatwaves on record for the
Willamette Valley, even for the Portland metro area. In addition to
these records, many daily high temperature records have been broken
as well; to view these, please refer to our Record Report (RER) via
weather.gov/pqr. Note you will have to click on previous versions of
our RER to find records broken for each day throughout this heat
event.

With temperatures in the evening starting off hotter later today and
several days of heating in buildings and structures without air
conditioning, Monday night will be the most brutal night of this
event, especially for urban areas such as Portland and Salem where
overnight relief looks very poor. NBM probabilistic guidance suggests
a 50-60% chance Portland`s inner eastside and St Johns will not fall
below 70 deg F Monday night and a 35-45% chance in Salem. Even if
temps do dip into the upper 60s tonight, it would likely only be for
one hour or less. After four days with high temps near 100 degrees or
worse and limited overnight relief, Monday night and Tuesday have the
potential to be the most dangerous portion of this prolonged heat
event in regards to heat-related deaths and/or heat-related
illnesses. This means it will still be a good idea to stay hydrated
and out of the direct sun. Do not forget about any pets and/or
outdoor plants you may have, as gardens will need frequent watering
and pets will need plenty of water and shade. It will be best to walk
dogs during the morning hours or late evening when temps will be
relatively cooler and surfaces such as concrete and asphalt will no
longer be hot enough to burn their paws. It never hurts to check on
your friends, family, and neighbors as well if they do not have
access to air conditioning.

One little wrinkle to the forecast on Tuesday is some weak vorticity
lifting northward from California, which will enhance instability
over the Cascades. For locations west of the Cascades, forecast
soundings show a fairly impressive stable layer between 900-800 mb,
which will limit surface-based instability for locations west of the
Cascades. While mid-level lapse rates steepen impressively and
MUCAPE values increase, soundings continue to suggest we will not
have enough moisture for thunderstorms to develop. At best, some
cumulus clouds developing along and near the Cascade crest appear to
be the most likely outcome. However, there may be some fire weather
implications with the increasing instability, which is discussed
below in the fire weather discussion.

Low-level flow turns decisively onshore Tuesday night into
Wednesday, bringing an end to the most intense heat. That said, WPC
cluster analyses strongly suggest positive 500 mb height anomalies
will last all the way through mid-July. This will keep the marine
layer shallower than usual, and limit the effectiveness of onshore
flow to cool inland areas. This will also make it very difficult for
morning cloud cover to develop for inland areas away from the coast.
So although the most extreme temps will be over with late this week
into next weekend, don`t expect a refreshing blast of cool air unless
you live along the coast or in the coastal valleys. Temperatures will
likely remain 5-10 degrees above climatological averages through at
least early next week (keep in mind climatological normals for high
temps this time of year are in the lower 80s over the Willamette
Valley). No rain is in sight for the foreseeable future.  -TK/Weagle

&&

.FIRE WEATHER...Monday afternoon through Tuesday...Issued a Red Flag
Warning for fire weather zone 685 for Monday afternoon and early
evening, which covers the southern Willamette Valley. This headline
was issued due to breezy northerly winds expected over the south
valley today with gusts up to 25 mph or so to the south of Salem,
including the Eugene-Springfield area. Given these gusty winds will
be occurring when relative humidity values are in the teens, any
grass fire that does start will have the potential to spread rapidly
towards the south. A similar setup is in store Tuesday afternoon,
however winds are trending slightly weaker and are currently just
shy of meeting our criteria for a Red Flag Warning. So, will hold off
on issuing another Red Flag Warning over the south Valley for
Tuesday afternoon, but will be watching trends closely. That said,
fine dead fuels will be very receptive to ignition and spread, so it
would not be surprising to see a few "median strip" type fires
caused by careless smokers throwing their cigarette butts out their
window while driving. Vehicles dragging chains and the like can also
create sparks which have the potential to ignite wildfires. The
bottom line is fire danger will still be significant on Tuesday and
extreme caution should be exercised with fire, especially for inland
areas below 2000 feet in elevation, where fuels are the driest.

The other potential fire weather concern is in the high Cascades
Tuesday afternoon. This is when model soundings continue to show
steepening lapse rates in the presence of thermal low pressure,
which can promote deeper columns in any fires which may start.
However, after some coordination with fire partners and neighboring
NWS WFOs, it appears our live 100-hr and 1000-hr fuels in the higher
Cascades are not quite dry enough yet to support rapid fire spread
if dry/unstable conditions were to materialize over the Cascades on
Tuesday. Therefore, have decided to hold off on issuing any fire
weather headlines in the Cascades.  -TK

&&

.AVIATION...Strong high pressure over the region will maintain
clear skies, along with hot temperatures today and tomorrow
(Tuesday). As a result, expect the potential for high density
altitude effects on takeoffs this afternoon into the early
evening. As the air mass along the coast cools tonight, we`ll see
see a 15-30% chance for patchy IFR stratus and fog. Any patchy fog
that develops could result in visibility reduction. Winds weaken
below 5 kt after 04-06z Tue as pressure gradients weaken.

PDX AND APPROACHES...High pressure will maintain VFR under clear
skies through the TAF period. Northwest winds weaken overnight,
strengthening in the afternoon but remaining below 10 kt.  -Alviz


&&

.MARINE...High pressure well-offshore will maintain gusty
northerly to northwesterly winds early this week. Tightening
pressure gradients will lead to wind gusts up to 25 kt through
Tuesday evening, mainly for the outer waters (10 to 60 NM out)
between Cape Falcon and Florence, OR. Therefore, the Small Craft
Advisory was extended for these locations through 8 PM Tuesday.
Pressure gradients ease Tuesday night through early Wednesday
afternoon, weakening winds below small craft conditions. Seas will
mainly be wind-driven, between 3 to 5 feet. After mid-week,
pressure gradients tighten again and northerly to northwesterly
winds will likely (60-80% chance) re-strengthen to small craft
conditions. This would build seas up to around 6 to 8 feet.  -Alviz

&&

.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...Small Craft Advisory until 8 PM PDT Tuesday for PZZ272-273.

&&

$$

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