NWS Portland, OR wrote its last area forecast discussion before the first event at Sep 9, 2:23 PM PST, 37 minutes earlier.
Area forecast discussion, Sep 9, 2:23 PM PST, 37 minutes before
Area Forecast Discussion
National Weather Service Portland OR
323 PM PDT Fri Sep 9 2022
Updated aviation and short-term sections.
.SYNOPSIS...A strong east wind event is on tap for today into
early Saturday. This will bring critical fire weather conditions,
above normal temperatures, and smoke and haze in various quantities
for different parts of the area. A southerly flow reversal Sunday
into Monday will lead to a strong onshore push which will replenish
moisture for lower elevations, along with a cooling trend next week.
&&
..DISCUSSION (through Thursday)...Water vapor satellite imagery at 3
PM shows tremendously dry mid levels as northeast flow continues
across Oregon and Washington behind an upper trough which is diving
southeastward towards the Great Basin. Below normal temperatures
continue as the cool air mass associated with this trough has become
entrenched across eastern Oregon and Washington, while west of the
Cascades temperatures are running a solid 10 degrees above normal as
east flow is downsloping across the Cascades.
The North Bend minus Spokane pressure difference has increased to
15.4mb as of 2PM (which is over-performing a bit from what guidance
has suggested), and unsurprisingly wind speeds have spiked in
response. Gusts to 40 mph have been observed in many locations,
including at PDX with the onset of the easterly surface flow this
morning from the Gorge. Overall, HREF is suggesting peak gusts for
most areas will be 10-15mph less than they were during the 2020
Labor Day event, so we'll continue to message the possibility of
gusts to around 25-35mph across much of the Willamette Valley, 35-
45mph near the Portland/Vancouver Metro, and 45-55mph across the
high Cascades and exposed areas in the Foothills this evening.
Overnight tonight, the event will turn into more of a classic gap
flow event, where areas within and downwind (i.e., west) of the gaps
in the Cascades and Coast Range - most notably the Columbia River
Gorge - will experience their highest winds. The mean of the HREF
ensemble is suggesting gusts to 50+mph through the west end of the
Columbia River Gorge tonight, which seems reasonable given the
forecast maximum pressure difference of roughly 8mb from Astoria to
the Dalles for early Saturday morning.
The CAMs have not been doing a great job of resolving where the best
mixing of strong winds a few thousand feet above the surface will
reach the ground thus far during this event, and so it's doubtful
they will do well tomorrow either. Still, it's worth noting they're
suggesting another burst in the northern lowlands when surface
heating begins tomorrow morning. This seems like a reasonable
possibility given forecast soundings are advertising still a fair
amount of wind even just a thousand feet above the ground at that
time, though the strong winds aloft will be quickly easing as the
gradient weakens with the northeastward shift of the coastal thermal
trough and resultant moderating temperatures east of the Cascades.
As a surface low moves up the coast Saturday and Saturday night, a
southerly flow reversal will overspread the forecast area from the
southwest to bring in cooler conditions and increase low level
moisture, finally assuaging some fire weather concerns for many (but
not all) areas; more details on that follow in the fire weather
discussion.
The other concern is wildfire smoke. DEQ's website suggests air
quality has deteriorated into the moderate category for many
locations, including (1) the Portland Metro where smoke has entered
the area from wildfires to our north and east, and (2) the Eugene
and Corvallis areas where smoke has arrived from primarily the Cedar
Creek Fire near Oakridge. The particulates resulting in this reduced
air quality are PM2.5, which are particularly hazardous to human
health, so staying inside and keeping windows closed if possible is
recommended. It is uncertain what will happen with air quality
across the area tonight into tomorrow, but the HRRR smoke model
suggests additional smoke will filter into the region from the east
due to the strong winds.
Saturday will also be a hot day, and some locations will have the
potential to experience record high temperatures as readings climb
into the mid to upper 90s inland and low 80s to locally 90 along the
coast. NBM continues to hint at this potential heat for coastal
communities as it advertises a 60% chance for highs above 85 degrees
at Astoria. The one exception to the heat inland will be in parts of
Lane County where the smoke concentration is the greatest and high
temperatures could be cut several degrees short by the smoke's
limiting effect on incoming short wave radiation.
The CAMs are hinting that some convection could fire along the
leading edge of the cold front from the offshore low Saturday
evening, though no members of either the EPS or GEFS ensembles are
putting QPF anywhere in the area and soundings suggest the moisture
will be above 600mb (except along the coast where there will be some
marine moisture). Given the conflicting data, a 20% chance for
showers was added to much of the area tomorrow evening/night,
meaning there will be a four times greater probability that rain
will not fall than that it will. Anything that falls will likely
only be a few sprinkles, as is often the case with virga.
Sunday, onshore flow keeps the area much cooler compared with
Saturday, and the southwest to west flow should drive much of the
smoke out except in the immediate vicinity of fires. (Unfortunately,
this could result in a wave of low level smoke surging up the
Willamette Valley into southern Washington Saturday night into early
Sunday morning. But even so, the front is likely to loft whatever
low level smoke is present so that it is no longer concentrated near
the surface.)
The upper low finally passes above the area Monday, deepening the
marine layer and likely resulting in drizzle for low elevations both
Monday morning and possibly Tuesday morning as well. The EPS
ensemble even has several members producing QPF for PDX Monday
morning, indicating the drizzle could reach inland locations too.
Overall, the pattern for early to mid week next week looks much
cooler; according to cluster analysis there isn't a whole lot of
spread among the ensemble members in the upper level synoptics, and
according to NBM there isn't much spread in the low level weather
conditions forecast by those members either. NBM gives around a 75-8
5% chance that highs will not surpass 80 Tuesday through Thursday of
next week. -Bumgardner
&&
.FIRE...Significant offshore wind event is underway this
afternoon as a well defined thermal trough resides along the CA and
OR coasts while surface high pressure builds over the Columbia River
Basin, promoting moderate to strong east winds over much of
northwest OR and southwest WA. Relative humidity values are
generally in the teens across the area with a few obs showing single
digits in Willamette National Forest. Red Flag Warnings remain
largely on track with respect to timing and forecast details. Expect
winds to peak tonight into early Saturday over the higher terrain
and through the Gorge, with some gusts to 50 mph over exposed
terrain in the Cascades and 40-45 mph gusts in the Gorge and over
favored terrain in the Coast Range. For Willamette Valley, have
tweaked the wind forecast upward in the northern valley this evening
based on a few gusts to around 40 mph coming out of the Gorge into
PDX this afternoon. Otherwise, still generally expecting winds to
max out around 35 mph in the rest of the valley this evening, with a
relative lull overnight and winds then picking back up Saturday
morning. Overnight recoveries will be poor throughout the area,
struggling to reach 30 percent in most locations and especially in
the Cascades. Winds should diminish relatively quickly on Saturday
night as the thermal trough develops into a closed low and pushes
offshore, weakening the gradient. This will yield improving although
still relatively dry conditions for Sunday. /CB
&&
.AVIATION...00Z TAFs: Strong easterly winds continue throughout
the area with gusts as high as 45 kt at the highest terrain, and
around 30 kt through the Willamette Valley. Currently receiving
reports of LLWS but due to the uniformity of the wind speeds, have
omitted from the forecasts. Satellite imagery shows widespread
smoke from the Cedar Creek Fire pushing eastward over the southern
Willamette Valley including KEUG and KSLE. Seeing some reductions
to visibility due to smoke and haze, and there still remains the
possibility of seeing IFR level conditions if smoke settles
to the surface.
Elsewhere, will likely see some smoke aloft or haze due to nearby
fires, but not expected to be nearly as concentrated. Could see
some eddies forming on the leeward side of the mountains due to
downsloping and warming, although confidence is low. Easterly
winds will strengthen downstream of the Columbia River Gorge at
KTTD and Coast Range gaps such as KTMK and KAST through 06-09z
Saturday before gradually weakening thereafter.
For detailed Pac NW aviation weather information, go online to:
https://weather.gov/zse
KPDX AND APPROACHES...VFR conditions will persist through the next
24 hours. Will see very gusty easterly winds with speeds upwards
of 35 kt at times. Reports of LLWS below 2000 ft at +/- 10 kt, but
due to a lack of directional shear, have not included in the TAF.
Winds will ease slightly after 10Z Saturday, but not expected to
reduce significantly until later Saturday morning.
-Muessle
&&
.MARINE...A closed area of low pressure continues to push
northward along the coastline which, when combined with high
pressure inland, is creating very strong offshore flow. Expecting
gusty winds around 15 to 20 kt with gusts up to 25 kt throughout
all of the waters, easing from the inner waters westward
starting early this evening. Winds have been slow to increase
today, but have been sitting right along the Small Craft Advisory
wind threshold. However, seas remain elevated with hazardous,
choppy seas. Generally seeing seas around 7 to 9 ft at 9 to 10
seconds throughout the waters. These conditions will persist
through the evening, when they will begin to ease to closer to 5
to 7 ft. Will continue the Small Craft Advisory due to a
combination of winds and hazardous seas.
After this east wind event, will see a wind reversal as onshore
flow returns on Sunday. A southwesterly flow will usher in
monsoonal moisture from the decaying tropical storm off of the
California Coast. Could see slightly elevated winds at that time,
but do think they will be marginal. High pressure builds once
again bringing a typical summertime pattern to the region.
-Muessle
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 8 PM PDT Saturday for Central Oregon
Coast-North Oregon Coast.
Red Flag Warning until 11 PM PDT Saturday for Central Oregon
Cascade Foothills-East Slopes of the Central Oregon Coast
Range-Mt. Hood National Forest West of Cascade Crest-North
Oregon Cascade Foothills-North Oregon Coast Range-
Willamette National Forest-Willamette Valley.
WA...Red Flag Warning until 8 PM PDT Saturday for South Washington
Coast and West Willapa Hills.
Red Flag Warning until 11 PM PDT Saturday for Clark County
Lowlands-East Willapa Hills-Eastern Gifford Pinchot
National Forest Mt Adams Ranger District-Extreme South
Washington Cascades and Foothills.
PZ...Small Craft Advisory from 3 AM to 8 AM PDT Saturday for Columbia
River Bar.
Small Craft Advisory until 9 AM PDT Saturday for Coastal waters
from Cape Shoalwater WA to Cascade Head OR out 10 nm-Waters
from Cascade Head to Florence OR from 10 to 60 nm.
Small Craft Advisory until 3 AM PDT Saturday for Coastal waters
from Cascade Head to Florence OR out 10 nm.
Small Craft Advisory until 3 PM PDT Saturday for Waters from
Cape Shoalwater WA to Cascade Head OR from 10 to 60 nm.
&&
www.weather.gov/portland
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