605
FXUS66 KPQR 030426 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
926 PM PDT Tue Jul 2 2024

Aviation Discussion Updated...

.SYNOPSIS...Warm and dry conditions persist through mid week
before a drastic warmup begins Thursday. High pressure
intensifies through the end of the week leading to dangerously
hot temperatures through Sunday. Temperatures may moderate
slightly to start next week but will remain hot well into next
week.

&&

.SHORT TERM...Now through Wednesday Night...Sunny skies prevail
across most of the area this afternoon with the exception of
some lingering marine cloud cover along the south Washington and
far north Oregon Coast. Observations show temperatures in the
70s across most inland locations, while the marine influence is
holding temps down in the 60s for coastal locations. In the
upper levels, the region remains under dry northwest flow on the
periphery of strong high pressure centered well off the
California coast which will become the dominant weather feature
through the next seven days.

Expect similarly pleasant conditions on Wednesday as the area
remains under the influence of northwest flow aloft. Inland
temperatures will warm a few degrees into the low 80s as high
pressure begins to shift closer to the coast, resulting in
modest 500 mb height rises and 850 mb temps climbing into the
13-15 C range. /CB

.LONG TERM...Thursday through Tuesday...A prolonged heatwave
will begin on Thursday as the strong upper level ridge over the
Pacific shifts closer to the coast and sends 850 mb temps into
the the low 20s Celsius. Current guidance has nudged inland
highs upward into the mid 90s on Thursday afternoon, with around
a 20 percent chance to reach 100 degrees through the Willamette
Valley. Heat will peak Friday through Sunday as high pressure
continues to build and shifts slowly inland near the CA/NV
border, with the ridge axis extending up the West Coast into
northern BC. As a result, probabilities to surpass 100 degrees
are above 70 percent across the interior lowlands both Friday
and Saturday and remain above 60 percent through Sunday. The
highest temperatures of the week look to occur on Saturday as
highs are expected to climb to around 105 degrees in the
lowlands. Notably, the probability to exceed 110 degrees ranges
from 15-35 percent on Saturday, and around 10-15 percent both
Friday and Sunday. Overnight lows will also be running quite
warm, likely staying in the mid 60s or above and possibly
struggling to drop below 70 in the Portland metro Friday night
and Saturday night, limiting the amount of relief during the
overnight hours. Given the high confidence in temperatures over
100 and the duration of the event, have upgraded the Excessive
Heat Watch to an Excessive Heat Warning from Thursday afternoon
through Sunday evening. May need to consider adding the the High
Cascades to the warning or placing them under an advisory in
future forecast cycles, but opted to delay that decision for now
as advisory level heat likely will not materialize in the
Cascades until Friday. In terms of historical context and given
the low end probabilities to exceed 110 degrees, it is not out
of the question that this event could rival the June 2021 event
or certainly the August 2023 event in terms of magnitude.
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 beyond.

The ridge axis begins to shift east of the region Monday into
Tuesday, but temperatures respond very slowly, only dropping
into the mid 90s and maintaining a 25 percent chance to hit 100
degrees 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 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. /CB

&&

.AVIATION...Persistent high pressure over the region maintains
weak onshore flow. Widespread VFR conditions across the airspace,
except for MVFR CIGs at KAST. Expect these flight conditions to
persist through at least 10Z-12Z Wednesday. There may be
backbuilding of clouds along the Cascades around 12Z Wednesday,
potentially bringing MVFR conditions (10-30% probability) to
terminals north of KPDX, with KTTD having a higher probability
(30-50%). Northwest winds with gusts up to 25 kt along the coast
and 20 kt inland continue until around 06Z Wednesday, then become
light thereafter.

PDX AND APPROACHES...VFR conditions will persist through most of
the period. Around 10Z Wednesday, backbuilding of clouds along the
Cascades could result in MVFR conditions (10-30% probability) in
and around the terminal. Northwest winds with gusts up to 20 kt
possible until 06Z Wednesday, decreasing and remaining light
through the TAF period.
-JH

&&

.MARINE...High pressure over the northeast Pacific with a
thermally induced low pressure over California/Oregon and the
Great Basin, which will persist through the remainder of the week.
This will result in north/northwest winds across all waters.
Winds will generally peak in the afternoon and evening hours each
day with gusts up to 30 kt. Small Craft Advisory remains in place,
and will likely to continue through much of the week. Marine
conditions remain more wind driven resulting in 5 to 8 ft seas
through the week. /42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

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

PZ...Small Craft Advisory until midnight PDT tonight for PZZ251>253.

     Small Craft Advisory until 3 AM PDT Wednesday for PZZ271>273.
&&

$$

www.weather.gov/portland

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