601
FXUS66 KPQR 080940
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
239 AM 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 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.

   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. The steepening lapse rates in the presence of
thermal low pressure may end up being more of a fire weather concern,
as it 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. West of the Cascades, fine fuels are the main concern right
now as those are most dry and ready to burn. There will be some
increase in northerly winds Monday afternoon for the Willamette
Valley and Coast Range, but it does not appear sufficient to meet Red
Flag Warning criteria. 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, although
there is no Red Flag Warning today, fire danger is still significant
and extreme caution should be exercised with fire, especially for
inland areas below 2000 feet in elevation, where fuels are the
driest.

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

&&

.AVIATION...Strong high pressure over the region will maintain
clear skies, along with hot temperatures on Monday. 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 patchy IFR stratus and fog re-form.
Improvement to VFR likely by 16Z Monday. Northwest winds increase
this afternoon along the coast 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 later
this afternoon. /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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