Heat in Washington, August 7 to 8, 2022

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1055 AM PDT Sun Aug 7 2022

Updated aviation and fire discussions

.SYNOPSIS...Hot temperatures are expected to continue into Monday as
an upper ridge lays over the Pacific NW. Temperatures will then cool
as a Pacific cutoff begins to near the coast through the week. The
low will begin advecting moisture north into the area, increasing the
chance of showers and thunderstorms for select areas through early
Wednesday. A drier trend will take hold for the latter half of the
week.

&&

.DISCUSSION...Today through Saturday...As an upper ridge lays across
the Pacific Northwest, caught between a large cutoff low offshore of
northern California and a shortwave trough over Montana, clear skies
can be found across OR and WA. The one exception is a surge of marine
fog and stratus moving north along the central OR coast. The
subsident ridge has resulted in low humidity settling across the
higher terrain, and a surface thermal trough stretching over the
central Willamette Valley up over Long Beach, WA has helping draw in
the drier warmer air from central OR. Warm overnight lows right now
and the expected clear skies will combine to bring the warmest
temperatures of the weekend today, with upper 90s in most of the
inland valleys, with a few places seeing triple digits as
high as 102. The higher terrain will see mid 80s to low 90s, while
the coasts remain in the mid 60s to mid 70s, though further north
where the surface trough will linger such as near Astoria, they will
likely see some readings in the mid 80s. Some hazy skies will exist
this morning from nearby fires, but nothing much at the surface
besides right near the fires, such as eastern Lane County by the
Cedar Creek Fire. Watching the smoke produced yesterday and its
eventual drift overnight, there doesn't seem to be enough to affect
the forecasted temperatures, so did not lower anything. The surface
thermal trough will be pushing east late this morning back over the
Cascade Crest, meaning gusty east winds over the Cascades should be
trending slower by noon and into the afternoon. HREF members continue
to show the potential for a few showers or thunder near or east of
the Cascade Crest in Lane County, kept a slight chance mention just
in the farthest southeast corner. This will likely occur in the late
afternoon into the early evening. Overnight, as the offshore cutoff
low starts slowly moving toward the coast, a flow reversal along the
shore in response to the surface trough moving north will allow
cooler marine air to surge north and inland over central OR.  A few
fingers of the jet ahead of the upper low will push north into OR
overnight, allowing for some lift potential. Several HREF members
showing some spotty showers possible to surge north early Monday
morning across the forecast area. Have added a 10-20% chance for
these. Moisture up in the -10 to -20C layer may be just enough for a
roll of thunder, mainly along the Cascade crest.

With the upper ridging breaking down slightly with the nearing of the
upper low, along with the increase in moisture from the south, look
for temperatures on Monday to be several degrees cooler. The areas
in the current Heat Advisory will still see temperatures in the low
to mid 90s, hence the Heat Advisory expiration time staying at 8pm
Monday. Additional moisture moving up will continue to keep a slight
chance of showers over the Cascades Monday afternoon. Monday night,
the jet on the forward side of the upper low will strengthen over
southern OR to create additional lift over the forecast area.
Monsoonal moisture surging north from the Desert Southwest will aid
in a 20% chance of showers across much of the area Monday night into
Tuesday morning. The whole atmospheric column will begin cooling as
the low nears, resulting in cooler temperatures, especially with
additional clouds.

Tuesday night into Wednesday, almost all deterministic and ensemble
models show the upper low north just offshore of the OR coast, to
spread in cooler air and and bring breezy winds. ECMWF EFI showing
some higher values along the Cascades for Wednesday, indicating an
anomaly. Temperatures will be back toward normal for mid-August.

The cutoff low is then shown to stall a bit off of Vancouver
Island Thursday and Friday, maintaining onshore flow and seasonable
conditions. WPC cluster mean keep the weak troughing just offshore
for Saturday as well, supporting the dry and just above normal
temperature forecast.  /Kriederman

&&

.FIRE...With an upper level subsident ridge over the PacNW and a
surface thermal trough over the Willamette Valley early this
morning, easterly winds over the Cascades have brought in drier
air. Some gusts in the 10-25 mph range with drops in humidity into
the 20-35% range early this morning show spotty Red Flag
conditions over the mountains. With the surface thermal trough
forecasted to start moving back east to be over the Cascades again
by early afternoon, expecting the east winds to peak late this
morning into early afternoon. This trend is well captured by the
latest hi-res model guidance. RH will remain low today with hot
temperatures, but the threat of RFW conditions will likely drop
off quickly by mid afternoon with the decrease in winds. Have
therefore trimmed back the end time of the Red Flag Warning to 3
PM this afternoon. There is still some mid-level instability to
cause concern, however with the more stable upper airmass, the
concern is lessening.

An upper low off the northern California coast will slowly lift
northeastward Monday through Wednesday, resulting in a prolonged
period of southerly flow aloft over the district, cooling
temperatures and advecting in additional moisture. This will
increase the chances for showers and thunderstorms Monday through
Wednesday morning, mainly over the Cascades during the afternoon
and evening hours, however some spotty activity may be observed
across the district. Tuesday appears to be the highest chance for
thunderstorms as moisture and instability will be on the increase.

&&

.AVIATION...18Z TAFs: VFR conditions are expected to prevail
through 18Z Monday for the inland TAF sites with increasingly
hazy skies due to elevated smoke coming from regional wildfires.
May see some reduction in slant-wise visibility at times,
especially from KSLE to KEUG. Surface visibility reductions due to
smoke are not expected at this time.

Although satellite and surface weather observations from 1730Z
Sunday showed clear skies at KAST and KONP, marine stratus was
hugging the central OR coast from Florence to Newport due to a
southerly wind reversal. The southerly wind reversal is expected
to begin pushing northward up the coast this evening into tonight,
likely making it to KAST by 09-12Z. Expect low stratus and fog to
accompany the southerly wind reversal, with cigs as low as 100-200
feet and dense fog likely at KONP after 02-03Z and cigs as low as
200-300 feet at KAST with surface visibility reductions also
likely after 10Z. The main forecast challenge is determining how
far inland the marine stratus deck will push into the southern
Willamette Valley, if at all. It appears the stratus layer will be
too shallow to make it all the way to KEUG, however the stratus
layer is expected to deepen a bit between 12-16Z. This is when the
HREF is showing around a 30 to 40 percent chance for cigs around
1000 feet or less at KEUG. For now, have decided to only bring
scattered cigs into KEUG Monday morning, but a broken stratus deck
cannot be completely ruled out.

For detailed Pac NW aviation weather information, go online to:
https://weather.gov/zse

KPDX AND APPROACHES...Expect VFR conditions to continue through
18Z Monday. Skies may become a bit hazy Sunday afternoon as upper
level smoke coming from the Cedar Creek wildfire to the south
drifts northward towards southwest WA. Surface visibility
reductions are not expected, however slant-wide visibility may be
impacted at times Sunday afternoon into Sunday night. -TK

&&

.MARINE...High pressure offshore continue northerly winds across
the waters with gusts near 20 kt this morning over the outer
waters. Nearshore, a ridge of high pressure continues to develop
over the south Oregon coast which will spread southerly winds
northward across the waters, reaching the southern zones this
morning, but not reach the south Washington waters until late
Sunday night. The southerly wind reversal is usually accompanied
by a shallow stratus layer or fog which can result in rapidly
deteriorating visibility. Will need to closely monitor for the
dense fog potential. So far the sparse observations available
show visibilities above 6 miles, but locally fluctuating below 1
mile.

Seas will remain around 4 to 7 ft at 7 to 9 seconds with a
dominant northwesterly swell. /mh

For information about upcoming marine zone changes, go online to:
https://www.weather.gov/pqr/marinezone

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 3 PM PDT this afternoon for Mt. Hood
     National Forest West of Cascade Crest-North Oregon Cascade
     Foothills.

     Heat Advisory until 8 PM PDT Monday for Central Columbia River
     Gorge-Greater Portland Metro Area-Upper Hood River Valley-
     Western Columbia River Gorge.

WA...Red Flag Warning until 3 PM PDT this afternoon for Extreme South

     Washington Cascades and Foothills.

     Heat Advisory until 8 PM PDT Monday for Central Columbia River
     Gorge-Greater Vancouver Area-Western Columbia River Gorge.

PZ...Dense Fog Advisory until 2 PM PDT this afternoon for Coastal
     waters from Cascade Head to Florence OR out 10 nm.

&&

www.weather.gov/portland

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