060
FXUS66 KPQR 031038
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
338 AM 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 Sunday. Temperatures may moderate
slightly to start next week but will remain hot well into next
week.

&&

.SHORT TERM...Now through Thursday...Minimal change in the
forecast as the high pressure ridge builds today. Will see sunny
skies 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 in the morning. 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.

Thursday will be the first day of the more persistent warm up
as temperatures rise generally into the 90s for the 4th of July
holiday. While not necessarily as hot as we will see over the
weekend, the thermal trough will develop causing winds to become
north to northeasterly. This will "shut off" the northwesterly
flow aloft and thus cause even more warming at the
mid-elevations. The Excessive Heat Warning starts on Thursday
due to a combination of the initial stages of the high
temperatures but also the effects of it being a holiday weekend.
Know that if you`re planning on going near rivers and lakes,
they are still on the chillier side. -Muessle/CB


.LONG TERM...Friday through Tuesday...Synoptically, 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 heatwave. There have been minimal
changes in the temperatures overall and the pattern seems to be
consistent. Looking at Friday, Saturday, and now Sunday being
the warmer days, with the highest temperatures on Saturday.
Lower elevations will see the highest values near 105 deg F. The
Excessive Heat Warning remains in effect as major HeatRisk
encompasses much of the forecast area.

Some regions that are a concern, but will remain outside of the
warning are the Cascades. As it stands, temperatures are in
moderate HeatRisk, and due to vegetation type, will struggle to
see as high of daytime temperatures due to shading from the
solar radiation. However, if you`re out hiking or camping this
weekend, the risk for heat related illnesses is non-zero. Please
practice safe procedures like drinking ample water, taking
breaks often, and minimizing alcohol consumption.

For inland and Cascade valleys, probabilities for temperatures
greater than 105 deg F range from 20-50% on Friday and 60-80% on
Saturday. On both days, the highest probabilities lie along the
I-5 corridor at elevations below 300 ft. Sunday`s probabilities
have seen little change but the highest chances (around 70%)
continue to be within urban areas around Salem, Hillsboro,
Portland, Vancouver, etc. The Columbia River Gorge, especially
around Hood River will see around a 50% chance of 105 deg F or
more on Sat/Sun. The probability for temperatures greater than
110 deg F remain less than 25% on Saturday with Friday and
Sunday being minimal.

Based on some brief research, temperatures forecast -
specifically around Portland - are resembling the heatwave we
saw in late July of 2009. We saw a few days of highs in the 90s,
with low 100s for 2 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 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 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. -Muessle/CB


&&

.AVIATION...High pressure continues, with generally weak onshore
flow continuing for the near future. Marine stratus continues to
be the dominant impact at coastal terminals during nighttime
hours, with MVFR CIGS at KAST. KONP looks to trend VFR for the
rest of the night, as it looks like marine stratus is staying
offshore. KAST should remain MVFR until 18-20z, after which it
clears up and turn to VFR throughout daytime hours Wed. Coastal
terminals see only around a 20% chance of MVFR thresholds late in
the TAF period Wed night, as an increasing thermal trough may
switch flow offshore, keeping marine stratus off shore.

Most inland terminals will remain VFR throughout the period, with
light NW flow between 5-10 kt. The exceptions are KPDX and KTTD,
which could see some marine stratus building off the Cascades.
Currently around a 50-70% chance of high-end MVFR cigs between
12-18z Wed, after which it should clear up quickly. VFR conditions
dominate the rest of the TAF period.

PDX AND APPROACHES...Brief period of possible high-end MVFR cigs
due to marine stratus backbuilding off the Cascades between
12-18z. Around a 50-70% chance of cigs dropping to around 2500 ft.
Afterwards, VFR conditions return for the rest of the TAF period.
NW winds between 5-10 kt expected throughout the TAF period. -JLiu

&&

.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. The
previous Small Craft Advisory has ended, but a few stray gusts up
to 25 kt will still be possible for another hour or so, until
4-5am Wed. SCA conditions return early Wednesday afternoon to the
central and southern waters, with gusts up to 30 kt possible as
the thermal trough enhances winds. Expect similar conditions each
afternoon and evening as winds will closely follow a diurnal cycle
of stronger gusts up to 30 kt during afternoon/evening hours, and
decreasing below SCA criteria overnight and during early morning
hours. Expect wind-driven seas between 5-8 ft at 8 seconds
throughout much of the week. -JLiu

&&

.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 from 1 PM this afternoon to 11 AM PDT
     Thursday for PZZ252-253-272-273.
     Small Craft Advisory until 3 AM PDT early this morning for
     PZZ271>273.
&&

$$

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