National Weather Service Area Forecast Discussion for Long Beach, WA USA

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Area Forecast Discussion
National Weather Service Portland, OR or
209 pm pst thu jan 20 2022

.synopsis...high pressure will begin building into the region
tonight, both aloft and at the surface. this ridge of high pressure
is then expected to persist through early next week. this setup will
result in a prolonged period of calm and dry conditions along with an
increased potential for fog and/or low stratus across the interior
lowlands, mainly during the overnight and morning hours each day.

&&

.short term...through sunday...a weak cold front was pushing across
the coast range early thursday afternoon, and will continue to push
eastward towards the cascade crest the rest of today. south to
southwest surface winds were occurring ahead of this front, which has
resulted in very mild temperatures for this time of year. in fact,
the portland international airport was sitting at 60 degrees at 1:15
pm pst jan. 20th, which breaks the record high for the day. the old
record was 56 degrees, which was set back in 1961. vancouver was
sitting at 59 degrees at the same time, which ties the record high at
that site (set in 1968). expect temperatures to cool behind the cold
front later today as surface winds continue veering to the west.
decreasing cloud cover is also expected the rest of this afternoon
and evening along the east slopes of the coast range and across the
western half of the willamette valley, as westerly flow will result
in downsloping on the lee side of the coast range mountains. at the
same time, high pressure will be strengthening over the region. this
will help set the stage for areas of fog to develop this evening as
winds become light and variable, especially for the aforementioned
areas where clearing skies are most likely to occur. in addition to
the fog potential, there is also the potential for patchy light
drizzle tonight as a weak impulse aloft dives down from the north,
bringing an increase in low-level moisture and forcing for ascent.
that said, the drizzle forecast is more uncertain than the fog
forecast as forecast nam/gfs/rap soundings show differing moisture
profiles between 0 and 1 km. the nam/rap seem to favor patchy drizzle
tonight, while the gfs does not. would expect at least some drizzle
tonight though, at least along north-facing slopes in higher terrain
where moist upslope flow should be enough to wring out some moisture.

friday still looks to be a dry day as high pressure continues to
strengthen both aloft and at the surface. in fact, friday will mark
the first day of a prolonged stretch of dry weather that will last at
least fix to six days (discussed below in the long term discussion).
with strong high pressure in place friday through the weekend, expect
subsidence inversions each night and calm winds. this setup is
favorable for widespread low stratus and/or fog to develop across the
interior lowlands friday night and saturday night, which should
linger through the morning hours on saturday and sunday. the low
mixing heights combined with the light and variable winds will most
likely result in air stagnation concerns, which could eventually
result in decreasing air quality as time goes on. the other forecast
challenge is the high temperature forecast on saturday and sunday due
to uncertainty regarding how widespread fog will get overnight and
how long it will linger into the following day. if fog and/or low
stratus is stubborn to lift, then high temperatures on saturday and
sunday will most likely be around 40 degrees in the lowlands. if fog
and/or low stratus is able to scatter out for the afternoon hours,
then highs should be in the low to mid 50s with sunshine. the nbm 1d
viewer continues to pick up on this uncertainty well, with the 10th
to 90th percentile for high temperatures ranging from 40 degrees to
around 55 degrees from portland to eugene. the current forecast is in
between these two outcomes, utilizing the nbm 50th percentile. -tk

&&

.long term...sunday night through thursday...the long term forecast
will be dominated by a persistent ridge over the eastern
pacific, which models and their ensembles suggest will extend into
the pacific northwest. this will continue to bring calm, dry, and
mild weather to the region through at least wednesday afternoon. this
means the air stagnation concerns that are expected to begin saturday
night are likely to remain a concern well into next week. due to the
prolonged nature of this potential air stagnation event, it is
possible that air quality will slowly worsen over time next week.
this is not a guarantee though, as there are many factors aside from
the weather that play a role in air quality. one thing that is more
certain is the continuation of low stratus and/or fog over the
interior lowlands during the overnight and morning hours each day.
while it is impossible to determine the details this far out in
time, would expect more low stratus rather than fog heading into
next week since the ground will be drier by then due to several days
in a row with no precipitation and some potential sunshine.

long range models are starting to show a breakdown of the ridge
late in the forecast with a shortwave trough pushing south from
the gulf of alaska wednesday night into thursday. however, with the
persistent stationary high pressure ridge in place, it will take a
system with a bit more energy to weaken it. there is still quite a
bit of model uncertainty at this point in whether or not rain will
return wednesday night into thursday, so it is far too soon to tell
exactly when the dry weather pattern will break down. -tk/muessle

&&

.aviation...00z tafs: northwest flow aloft, along with moist,
onshore low level flow, through this evening. a mix of mvfr and
vfr conditions through the interior valley, expected to become
predominately vfr by 00z. at the coast, onshore flow will
maintain low stratus through this evening. expect ifr to lifr
conditions to persist through 03z friday, especially along the
central oregon coast, with model guidance suggesting a chance
for improvement to mvfr afterwards. high pressure builds tonight
as the flow aloft becomes more northerly. models show the marine
layer deepening to around 4000-5000 ft which could produce some
drizzle, especially across the northern forecast area. cigs
across the interior are expected to lower to mvfr after 06-07z as
well. if there are any cloud breaks tonight, will likely see fog
develop, especially within the southern willamette valley. cigs
may lift to vfr around 20z friday.

for detailed regional pac nw aviation weather information, go
online to: https://weather.gov/zse

kpdx and approaches...mix of vfr and mvfr currently, but expect
mainly vfr conditions through 06-07z this evening. cigs will
likely lower to mvfr as the marine layer deepens tonight, along
with some patchy drizzle into friday morning. west winds around
10 kt will ease and become northwest by this evening. /dh

&&

.marine...high pressure will continue to build across the waters
through friday. northwest winds around 10-15 kt this evening will
turn more northerly as thermally induced low pressure along the
northern california and southern oregon coast increases the
pressure gradient over the coastal waters. north winds gradually
increase to around 15-20kt by friday evening, particularly off
the central oregon coast. the surface high pressure center will
drift northward allowing for some offshore component to the wind
through the weekend. winds should also ease to around 10-15 kt by
sunday. high pressure weakens somewhat early next week with
settled weather expected to continue.

seas around 6 to 8 ft at 14 seconds will continue to build up to
9 ft through tonight before gradually easing back to around 7 to
8 ft on friday. another long period northwesterly swell is
expected to move in on saturday with a period of around 15
seconds and seas hovering around 7 ft. seas gradually build again
sunday into monday as a westerly swell moves in, bringing a
chance of seas reaching 10 ft. /dh

&&

.pqr watches/warnings/advisories...
or...none.
wa...none.
pz...none.
&&

$$

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