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FXUS66 KPQR 081753 AAA
AFDPQR

Area Forecast Discussion...UPDATED National Weather Service Portland
OR 1051 AM PDT Mon Jul 8 2024

Updated aviation discussion...

.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 continues to build today and Tuesday; each day will be a couple
degrees hotter than the last. 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...Today through Sunday...Dangerously hot weather
continues for all but the coast, with day after day of record
breaking temperatures for the interior.

KEY POINTS:

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

2. High temperatures will likely approach or reach 105 degrees for
the Willamette and Hood River Valleys today and Tuesday.

3. Tonight will be even slower to cool off in urban areas than the
last several. 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.

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

High temperatures finally reached 100 degrees at PDX after two days
of falling just a degree short. Although this won`t be a record-
setting period of 100 degree temps for Portland, it probably will be
for Salem and Eugene, both of which have exceeded 100 degrees for
the last three days. This will, however, almost certainly tie heat
waves in July 1941 and August 1981 for the most consecutive days at
or above 99 degrees at Portland Airport with five. 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.

Now that the NW flow has ended across BC and eastern WA, the
Portland metro and SW Washington will be able to heat up a couple
more degrees versus the past few. The 00z EC ensembles show good
agreement with the 00z GFS deterministic that 850 mb temps will warm
from around +22 deg C over Portland Sunday afternoon, to +24 to +25
deg C Monday afternoon. This suggests the potential for temperatures
to be 3-5 degrees hotter for SW Washington and the Portland metro
area than what has occurred the past few days. Would not be
surprised to see a few Portland metro locations near 105 deg F this
afternoon. Salem and Eugene already had 850 mb temps near +24 deg C
on Sunday, so there will be little difference from Sunday to today
for those locations -perhaps they will climb another degree or two
to 105 deg F today and/or Tuesday.

With temperatures starting off the evening hotter and several days
of heating of buildings and structures, Monday night will probably
be the most brutal of this event, especially for urban centers such
as downtown Portland. NBM probabilistic guidance suggests a 50-70%
chance Portland`s inner eastside and St Johns will not fall below 70
deg F Monday night. After 4 days of temps near 100 degrees or worse,
with limited overnight relief, Monday night into Tuesday have the
potential to be the most dangerous portion of this prolonged heat
event.

For probabilistic guidance from the latest NBM regarding high temps,
refer to the probability-of-exceedance table shown below.

               Mon            Tue           Wed              July 8
July 9        July 10            100+ 105+    100+  105+ 100+ 105+
================================================ Kelso 70% 10% 75%
20%  0%     0% Portland* 90%   40% 99%   60%  5%  0% Salem 99%
55% 99%   75%  5%     0% Eugene 95%   40% 95% 40% 5%    0% Hood
River 95%   45% 99%   80% 20%     1%

The % of reaching 110 or higher is now at or less than 10% for all
areas. Given the way this heat event has been trending, confidence
is high we will NOT reach 110 degrees anywhere in the Willamette
Valley.

*Portland is for Greater Portland/Vancouver metro area.

It is worth mentioning again that the worst of this heat wave looks
to be today through Tuesday, so it will 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 cooler and surfaces such as concrete and asphalt will
no longer be hot enough to burn their paws.

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. So although the worst will be over at
that point, 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. No rain is in sight.  -Weagle

&&

.FIRE WEATHER...Monday 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 Red Flag Warnings. 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. As a
result, expect the potential for high density altitude effects on
takeoffs this afternoon into early evening. As the air mass along
the coast cools tonight, will see a 15-30% chance for patchy IFR
stratus and fog. Any patchy fog that develops could result in
Improvement to VFR likely by 16Z Monday. Northwest winds increase
this afternoon along the coast and southern Willamette Valley with
gusts to around 20 kt.


PDX AND APPROACHES...High pressure will maintain VFR under clear
skies. Northwest winds expected to increase to around 10 kt this
afternoon.    -Alviz/DH

&&

.MARINE...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 this week. Building high pressure today tightens
pressure gradients across the coastal waters with wind gusts up
to 25 kt possible by late afternoon. Have issued a Small Craft
Advisory for outer coastal waters south of Cape Falcon through
tonight. Seas mostly a mix of wave fetches, one at 1 to 2 ft from
the southwest, with the other from the west at 2 to 4 ft. As
such, overall combined seas stay in the 3 to 5 ft range through
mid-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...Small Craft Advisory from 5 PM this afternoon to 5 AM PDT
Tuesday for PZZ272-273.

&&

$$

www.weather.gov/portland

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