Wildfire in Oregon, August 1 to 31, 2022

Area Forecast Discussion
National Weather Service Portland OR
432 AM PDT Mon Aug 1 2022

.SYNOPSIS...Cooling trend begins today, although temperatures
still look to remain above seasonal norms through Wednesday. The
coast remains considerably cooler and will experience periodic
marine clouds and fog. Thunderstorms remain possible over the
central Cascades through Tuesday afternoon, though the bulk of
the activity should be focused east of the crest. Thursday will
be the coolest day before another potential warm up into the
weekend.

&&

.SHORT TERM...THROUGH WEDNESDAY NIGHT...The upper level pattern
this morning continues to feature a ridge extending from the
Great Basin to the Pacific Northwest with a quasi-stationary
cutoff low centered approximately 350 miles off the northern
California coast. Water vapor satellite imagery reveals the
ridge beginning to feel the influence of a shortwave trough
crossing northern British Columbia, which will bring about the
end of the prolonged heatwave and commence a gradual cooling
trend for the upcoming week. In the meantime, moist southerly
mid level flow between the ridge and the offshore cutoff low is
producing light, elevated shower activity riding over the top of
the entrenched marine layer in the coastal waters, with even
some lightning strikes noted along the southern Oregon Coast.
Radar also depicts a few echos moving northward through the
Willamette Valley, but these will likely have a hard time
producing any precipitation at the surface given the sizable dry
layer in place in the lower levels. Southerly flow is also
helping to advect a thin smoke layer aloft into the region from
ongoing wildfires in northern CA and southwest OR. This may lead
to some hazy skies today but should otherwise have little
impact on the forecast.

The main story today will be the start of a downward trend in
afternoon high temperatures as the ridge begins to flatten out
and produce modest height falls across the region. 850 mb temps
around 20 C should translate to afternoon highs near 90 in the
Willamette Valley, which while still running above seasonal
norms will represent an 8-10 degree cooling trend from recent
days across most of the area. Expect this trend to continue
through Wednesday, with highs topping out in the mid to upper
80s in the interior valleys both Tuesday and Wednesday
afternoon.

In terms of thunderstorm potential, mid level flow will turn
from southerly to more west-southwesterly today and Tuesday as
the offshore cutoff low retrogrades into the Pacific and away
from the region, which should focus the bulk of the shower and
thunderstorm activity south and east of the area for the next
few days. Can't rule out a few strikes near the crest of the
Lane County Cascades, but coverage should be more sparse than
what was observed on Sunday. /CB

.LONG TERM...THURSDAY THROUGH SUNDAY...Thursday is shaping up as
the coolest day of the week as the western Canada trough is
reinforced by another shortwave dropping over Washington, with
increased cloud cover and 850 mb temps around 12-14 C suggesting
highs in upper 70s to near 80 Thursday afternoon. There may
also be some increased shower potential associated with this
feature, but confidence in that scenario is low at this time.
Forecast confidence remains lower than normal from Friday into
next weekend, mainly owing to continued model struggles on how
to handle the evolution of the cutoff low as it lingers offshore
and possibly approaches the coast again late in the extended
period. This uncertainty is depicted by a rather large spread
both in deterministic solutions and ensemble clusters of 500 mb
height anomalies, which leads to a sizable range of outcomes for
forecast temperatures by the end of next week. Stuck close to
NBM 50th percentile guidance for now given the lower confidence,
which splits the difference with temp rising back into the mid
to upper 80s next weekend. Bottom line, the end of the week
could feature anything from temps near seasonal norms to rising
well into the 90s again depending on the evolution of the
synoptic pattern which will hopefully come into better focus in
the days ahead. /CB

&&

.AVIATION...12z TAFs: The familiar summertime pattern of VFR
inland and IFR/LIFR along the coast continues through Monday.
Expect conditions along the coast to start improving around 20Z
Monday with inland coastal locations such as KAST & KTMK
generally VFR with IFR conditions returning around 05Z Tuesday.
However expect IFR/LIFR to continue along the beaches. Inland
areas are expected to remain VFR through tomorrow, but there will
likely be some haze because of the smoke from the fires near the
OR/CA border that continues to lift northward into NW Oregon due
to southerly flow aloft. No significant impacts expected to
surface vsby but slant range vsby might be impacted.

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

KPDX AND APPROACHES...VFR with light northerly winds through
Monday. Smoke remains too thin to have an impact on surface
vsbys, but could impact slant range vsbys on approach through
Monday. /mh /42

&&

.MARINE...Buoy and satellite imagery, along with observations
from the USCG have prompted the issuance of a dense fog advisory
across all the waters. Visibilities will likely fluctuate between
4NM to less than 1NM at times through Monday afternoon. /42

Otherwise expect fairly benign weather for the next few days.
High pressure offshore and thermal low pressure inland will
maintain N-NW winds through at least midweek. Seas will remain
around 5 ft, 9 sec dominated by a northwesterly swell generated
off of Vancouver Island. There is a small, 1 to 2 feet, southerly
swell around 14-17 seconds reaching the waters through at least
mid-week.  /mh

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

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Dense Fog Advisory until 1 PM PDT this afternoon for coastal
     waters from Cape Shoalwater WA to Florence OR out 10
     nm.Columbia River Bar-Coastal waters from Cape Shoalwater
     WA to Florence OR from 10 to 60 nm.

&&

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