Wildfire in Oregon, July 12 to 31, 2021

Area Forecast Discussion
National Weather Service Portland OR
836 PM PDT Sun Jul 11 2021

Updated aviation and marine discussions.

.SYNOPSIS...Under predominantly zonal upper level flow, the area will
see largely tranquil weather conditions throughout the next several
days. Prevailing onshore flow will promote fluxes of marine moisture
and stratus each night, but surface heating will quickly burn off the
clouds each morning to promote warm afternoons everywhere except
along the coast. For the latter part of the week, a strong upper low
approaching our area from the Gulf of Alaska will lower heights and
bring more seasonable temperatures.

&&

.SHORT TERM...This evening through Wednesday...The mainly mellow
weather pattern continues as NW Oregon and SW Washington remain
under the influence of a zonal 500mb flow regime. Several short-
range models (i.e. the NAM, UWWARF, and RAP) agree that 500mb
heights will lower briefly tomorrow before rebounding Tuesday as a
weak shortwave trough traverses the northern part of our CWA. This
ripple in the flow aloft, being slightly stronger than the one that
passed immediately north of our area this morning, should promote a
deeper layer of clouds tomorrow. In addition, the movement of the
low towards our east will induce a stronger gradient favoring
another robust push of marine air Tuesday morning. As compared to
this morning, 1000-850mb relative humidity will be higher both
Monday and Tuesday mornings to also favor the aforementioned marine
push. To account for this, the sky coverage forecast tomorrow and
Tuesday were more or less a carbon copy of this morning's visible
satellite observations - except the areas of stratus were expanded
slightly and made to last for a bit longer (since a deeper marine
layer will be slower to burn off). Similar to this morning, there is
another slight chance for drizzle along the north coast, but
uncertainty is high so decided not to add it to the forecast.
Overall, not much change in the forecast through Tuesday.

Another point of concern in the immediate term was the decision as
to whether or not to add smoke for part of our area. Satellite
images shows diffuse, lofted smoke from the Bootleg Fire in south-
central Oregon which may move north in upper-level southwesterly
flow. Given that the HRRR smoke model suggests smoke will skirt our
southeastern CWA along the Cascades, and that visible imagery
depicts this plume nearing our area, have elected to add a mention
of haze for the eastern Lane Co. Cascades through early Tuesday
morning.   -Bumgardner

.LONG TERM...Wednesday through Sunday...Cluster analysis
portrays a low amount of uncertainty in the large-scale pattern for
the first portion of the long-term, with a general trend towards
lowering 500mb heights in advance of an approaching, deep trough. As
is often the case in patterns with a high pressure ridge towards our
east, the trough attempting to move in from the west is progged to
be "blocked". This may force it to become stationary or even
retreating westward for the middle to latter portion of the long
term period. This makes it difficult to discern which system will
have a dominant impact on temperatures.

This being said, the inclination is towards cooler temperatures for
Thursday through Saturday, during which time the cluster solution
with the highest number of total ensemble members is depicting lower-
than-normal (but only by around 30 meters) heights over our area. It
seems in each cluster solution favoring lower heights compared with
the others, the members from the ECMWF constitute a high proportion
of the total - not surprising given the Euro deterministic (often
the best in the long term) has trended the coolest. Not surprisingly
given it's day 7, Sunday the forecast becomes trickier with all four
clusters different. The NBM, with its IQR of 84-89F at PDX and 82-
87F at Eugene for probable high temperatures, suggests it will be
the first day in a gradual warming trend. -Bumgardner

&&

.AVIATION...Marine stratus is hugging the coast this evening
under north winds. The coastal winds are becoming more NW; as a
result low clouds are slowly advancing into the coastal valleys.
As of 0330z, IFR cigs were affecting KONP and were right on the
doorstep of KAST. Expect IFR cigs to fully move over KAST by 05z.
IFR/low MVFR conds should then affect the coast overnight,
lingering through Monday morning. The stratus will move inland
along the lower Columbia River late tonight with MVFR conditions
for KSPB and KKLS likely. It is uncertain if the clouds will make
it into the north Willamette Valley, and impact KVUO, KPDX, and
KTTD, but a weak upper level disturbance moving over the area
favors the possibility. Any marine stratus that may make it
inland Monday morning will rapidly clear to VFR conditions late
in the morning. The clouds along the coast will take longer to
clear, and may persist into Monday afternoon.

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

KPDX AND APPROACHES...VFR conditions will prevail through this
evening. The gusty NW winds early this evening should ease below
10 kt by 07z. There is a possibility that stratus will move up
the lower Columbia River valley tonight and possibly reach the
terminal between 12 and 17z Monday.  Weagle/TJ

&&

.MARINE...Marine forecast appears to be on track, and no changes
were made this evening. N-NW winds briefly touched gale criteria
near Florence late Sunday afternoon, but have since come down
and are in line with our forecast. The marine discussion from
this afternoon follows.  Weagle

A persistent weather pattern of High pressure across the waters
and a thermally induced low over NW California will continue
north waters across the coastal waters through the week. The
winds will be strongest in the afternoon and evening where gusts
up to 25 kt are likely, especially in the waters south of
Tillamook, Oregon. The high pressure weakens a tad on Monday and
Monday night which will make it hard for the north winds across
the south Washington and north Oregon coastal waters to have
gusts much above 20 kt, especially within 10 nm from the coast.
The small craft advisory headlines were therefore modified to end
earlier in the northern waters. The high pressure strengthens
Tuesday returning the afternoon gusty winds to the waters. The
north winds are expected to decrease again late in the week into
next weekend as a low pressure system moves towards the B.C.
coast north of the Washington coastal waters.

Seas will be a combination of fresh north swell and steep wind
waves. Swell periods will predominately be less than 9 seconds
and wave heights between 4 and 6 feet. The low-amplitude
northwest swell with a frequency of 14 seconds has decreased
today making it less of an influence on the significant wave
heights. ~TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 1 AM PDT Tuesday for Coastal waters
     from Cascade Head to Florence OR out 10 NM-Waters from
     Cape Shoalwater WA to Cascade Head OR from 10 to 60 NM.

     Small Craft Advisory until 11 PM PDT this evening for Coastal
     waters from Cape Shoalwater WA to Cascade Head OR out 10
     NM.

     Small Craft Advisory until 2 AM PDT Wednesday for Waters from
     Cascade Head to Florence OR from 10 to 60 NM.

&&

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