515
FXUS66 KPQR 032116
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
216 PM PDT Wed Jul 3 2024

.SYNOPSIS...Dry and warm through Thursday. High pressure
intensifies through the end of the week leading to dangerously
hot temperatures through at least Sunday. Temperatures may
moderate slightly to start next week but will remain hot well
into next week.

&&

.SHORT TERM...Now through Thursday night...Minimal changes in
the forecast as high pressure begins to build over our area.
Cloud cover has dissipated across most of the CWA, except for
portions of the south Washington coast. Enjoy the pleasant
weather this afternoon/evening while it lasts! Tomorrow will be
the first day of the more persistent warm up as temperatures
rise into the low 90s for interior valleys and 70s along the
coast for the 4th of July holiday.

While not necessarily as hot as what we will see this weekend,
the Euro model is showing a thermal trough developing tomorrow
(Thursday) which would "shut off" onshore flow and cause winds
to become more north to northeasterly. The GFS on the other hand
doesn`t have the thermal trough forming just yet, but either
way our air mass will begin to warm up with the ridge building
over us.

The Excessive Heat Warning remains in effect beginning 12 PM PDT
tomorrow due to a combination of the initial stages of the high
temperatures but also the effects of it being a holiday weekend.
We have also added a Heat Advisory for all of the Cascades
considering those who may have travel plans in the mountains.
Know that if you`re planning on going near rivers and lakes,
they are still on the chillier side.         -Alviz/Muessle

&&

.LONG TERM...Friday through Tuesday...Synoptically, we`re looking
at an intensifying ridge taking on the omega blocking pattern
as a trough digs southward to the west over the Pacific, and to
the east over the Rockies. This ridge will amplify through
Sunday which will lead to a prolonged, dangerous heatwave.
There have been minimal changes in the temperatures overall and
the pattern seems to be consistent. Fortunately, winds do not
look overly impactful in the long term.

Friday, Saturday, and Sunday are forecast to be the hottest
days, with temperatures soaring to 100 to 105 degrees F for
interior lowland valleys. The Excessive Heat Warning will go
through the entire 4th of July weekend as there will be
widespread major HeatRisk across northwest Oregon and southwest
Washington, west of the Cascades. Overnight temperatures will
also struggle to cool down, with lows forecast between 65 to 70
deg F within interior valleys from Saturday morning to at least
Monday morning. Heat exhaustion or heat stroke is possible for
anyone who is exposed to the heat without an effective way to
cool down, especially those who are particularly susceptible to
heat.

Some regions that are a concern, but will remain outside of the
Excessive Heat Warning are the Cascades. As it stands,
temperatures remain mostly within moderate HeatRisk, and
afternoon highs will struggle to climb as high due to shading
from the local vegetation type. However, if you`re out hiking
or camping this weekend, the risk for heat related illnesses is
non-zero. Thus, the reason why we decided to add a Heat Advisory
for the Cascades beginning 12 PM PDT tomorrow. Please practice
safe procedures like drinking ample water, taking breaks often,
and minimizing alcohol consumption.

Here are temperature probabilities for the Willamette Valley,
where the most intense heat is expected:

Greater than or equal to 100 degrees: 70-90%
Greater than or equal to 105 degrees: 50-60%
Greater than or equal to 110 degrees: 25-30%
Greater than or equal to 115 degrees: 5-10%

Based on some brief research, forecast temperatures (specifically
around Portland) are resembling the heatwaves we saw in late
July of 2009 and last August of 2023. We saw a few days of
highs in the 90s, highs around 100-105 for about 3 days,
followed by a return to the 90s for more days. Regardless of
exactly how high temperatures ultimately climb, confidence is
high in a prolonged period of hot temperatures with minimal
overnight relief, leading to dangerous conditions through this
weekend and possibly into early next week.

The ridge axis begins to shift east of the region Monday into
Tuesday, but temperatures respond very slowly, only dropping
into the mid to upper 90s in many locations all the way through
Tuesday. WPC ensemble clusters also maintain strong ridging
over the western CONUS into the end of next week, with the
Climate Prediction Center keeping the region under a moderate
risk (40% chance) for excessive heat through July 12. So,
although the hottest conditions are expected through this
weekend, people should be prepared to deal with the cumulative
effects of a long duration heat into at least the middle of next
week.       -Alviz/Muessle

&&

.AVIATION...High pressure persists, with weak onshore flow.
VFR conditions are expected, but a return of MVFR/IFR conditions
is possible (35%-45% probability) starting around 10Z Thursday.
Any lowered flight conditions along the coast will likely be
somewhat short lived as northerly/ slight easterly winds develop
through 15Z Thursday.

Generally VFR for inland terminals through the remainder of the
TAF period, with NW flow between 5-10 kt. Expects gusts up to 20
kt for KSLE through 05Z Thursday. These gusts are expected to
return each afternoon and persist through the evening.

PDX AND APPROACHES...VFR conditions for the rest of the TAF
period. /42

&&

.MARINE...High pressure over the northeast Pacific with a
thermally induced low pressure over California/Oregon and the
Great Basin. This pattern will persist through the remainder of
the week and likely into the start of next week. Small Craft
Conditions will develop across all the waters, with a brief
pause in conditions late tonight and into early Thursday
morning. Expect gusts up to 30 kt with similar conditions each
afternoon and evening as winds will closely follow a diurnal
cycle. Seas will be predominately wind-driven resulting in 5-8
ft at 8-10 seconds throughout the week. /42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Excessive Heat Warning from noon Thursday to 11 PM PDT Sunday
     for ORZ104>125.

     Heat Advisory from noon Thursday to 11 PM PDT Sunday for
     ORZ126>128.

WA...Excessive Heat Warning from noon Thursday to 11 PM PDT Sunday
     for WAZ202>210.

     Heat Advisory from noon Thursday to 11 PM PDT Sunday for WAZ211.

PZ...Small Craft Advisory until 3 AM PDT Thursday for PZZ252-253.

     Small Craft Advisory until 3 AM PDT Thursday for PZZ271.

     Small Craft Advisory until 5 AM PDT Friday for PZZ272-273.
&&

$$

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