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

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Area Forecast Discussion...updated
National Weather Service Portland, OR or
842 pm pst sun nov 27 2022

updated aviation section

.synopsis...post frontal showers across the lowlands will
diminish overnight with heavy snow accumulations across the
cascades by monday morning. active weather continues throughout
the week as additional storms system drop down from the north
bringing rounds of rain and high elevation snow throughout the
week. there remains a chance for light snow across the interior
lowlands thursday and friday.

&&

.discussion...through saturday...a low level cold front
associated with an upper level trough currently over alberta has
pushed east of the cascades. postfrontal showers will continue
across the area through this evening with rain accumulations
across the lowlands between 0.15-0.20" over the next 12 hours.
the cooler air mass will bring snow levels down to around 1500
ft in the south wa cascades and 2500 ft across the lane county
cascades. a piece of energy will split off from the parent low
to the north and dig south over eastern washington overnight.
this will bring the jet streak south over the area while
reorienting the 850mb winds more westerly. the synoptic lift
coupled with orographically enhanced snow showers will produce
heavy snow across the cascades into monday morning. snow amounts
should reach into 12-18" range with strong westerly winds.
blowing snow will pose a hazard to those travelling across the
passes. therefore, the winter storm warning remains in place
through 10 am monday for the wa and north or cascades and
through 4 pm for lane county cascades. have added an advisory
across the foothills in the or cascades as well for this evening
as accumulations will likely be impactful for travelers.
another impact from tonights system will be enhanced instability
from cold air advection aloft which will bring a chance of
thunderstorms, mainly to the waters and coastal areas, then
moving inland monday.

snow will decrease from north to south starting in the afternoon on
monday as the shortwave trough moves into the intermountain west, and
a shortwave ridge moves in. colder but drier air moving down in
the northwest flow will result in clear skies and cold temps
monday night. light snow showers will likely still be found in
the high cascades, but the surface pressure gradient turns
offshore as very cold air surges south out of canada and into
the columbia basin. in theory this should scour out any moisture
in the boundary layer keeping near the surface dry but a low
level baroclinic zone sets up just offshore creating uncertainty
in the qpf forecast. a shallow warm front may inject just
enough moisture to produce a light dusting on the valley floor
tuesday morning with such cold temperatures already in place.
nbm still shows a 20-40 percent chance of early tuesday morning
lowland snow. temperatures will warm and the light snow on the
grass will melt by lunch.

the next system in the series will move south along the british
columbia coastline tuesday sending a much more defined warm
front northeast across the area tuesday night. snow levels will
rise to around 3500 ft wednesday morning. temperatures will
warm a few degrees into the mid 40s in the interior lowlands
and upper 40s along the coast. expect heavy precipitation
wednesday afternoon as a 700mb deformation band drapes across
the area with a strong jet aloft providing good support. another
thing will be the strong prefrontal 850mb winds that could put
the coast range over the top to need a high wind warning
wednesday morning. the cold front will move onshore sometime
wednesday afternoon and cool, postfrontal showers will continue
overnight. chances for a trace to an inch of snow in the low
levels continue to increase sometime thursday into friday as
wrap around moisture continues within the cold air mass. the
next system from the gulf of alaska will be fast approaching
giving little reprieve from precipitation friday into saturday.
confidence is high that the long term will be wet but whether
the cold air will set up and stay in place long enough to
produce the perfect conditions for low elevation snow is too
early to tell. -bmuhlestein

&&

.aviation...06z tafs: cold and unstable air mass over the region
this evening in the wake of earlier frontal passage. west to
northwest 850 mb flow is resulting in shower activity this
evening, favoring the higher terrain. taf sites will experience
vfr with short-lived periods of mvfr during the early portion of
the 06z taf period. model guidance suggests an organized band of
showers will move through the forecast area late tonight through
early monday morning. at 0430z infra-red satellite imagery showed
a band of colder-topped clouds moving into northwest washington.
thus, expect increasing mvfr at all taf sites during the 09z to
12z period. high-resolution model guidance shows a 40-50 percent
chance of mvfr for the north interior taf sites overnight, but
increasing to 50-70 percent south of ksle. shower activity looks
to decrease from north to south after 15z monday, with the highest
mvfr threat continuing in the south interior valleys. predominant
vfr is expected monday afternoon through 06z tuesday. the
northwest 850 mb flow will maintain frequent mountain obscurement
through the 06z forecast period.

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

kpdx and approaches...a cool and unstable air mass will reside
over the terminal and vicinity through the 06z taf period.
predominant vfr expected through around 09z, but brief periods of
mvfr in showers will remain possible. an organized band of showers
is expected to move across the terminal and vicinity late tonight
through early monday morning for increased periods of mvfr.
showers diminish mid to late monday morning, with predominant vfr
late monday morning through 06z tuesday. there is a 10-20 percent
chance of brief ifr late tonight through monday morning,
especially for the tualatin river valley. weishaar

&&

.marine...a cold front continues to drop southeastward across the
waters off the southern oregon coast this afternoon. winds have
shift out of the west to northwest behind the cold front across
much of the waters. expect gustier winds out of the northwest to
return to the waters overnight. seas are currently hovering
around 10-13 ft across the northern waters and 10-11 ft across
the southern waters. seas appear likely to hold in the low to mid
teens through monday night. given seas will likely run several
feet higher across the outer waters, particularly beyond 30 nm,
the hazardous seas warning for tonight into monday looks on track.

as weak high pressure passes overhead monday night into
tuesday and winds weaken, expect seas to subside below 10 ft.
however, a developing low pressure near haida gwaii will then
drift southeastward towards the region and likely result in the
strongest cold front and attendant winds over the waters so far
this fall/winter season. solid gale force wind gusts of 35-45 kt
appear likely across the waters. there appears to be a 50% chance
that storm force wind gusts of 50 kt will even materialize at
buoy 29 and buoy 50 midweek. given a coastal jet will likely form
ahead of the front, the probability of storm force wind gusts
within 10 nm of the coast is even higher. due to these strong
southerly winds, seas will respond and climb into at least the mid
to upper teens wednesday and likely remain in the teens through
thursday. another storm system appears likely to bring another
round of strong southerly winds and increasing seas around next
friday or saturday.

the new moon today and monday will produce stronger tidal
currents than normal during the evening ebb cycle. those moving in
and out of harbors and crossing coastal bars should use caution
and be aware of any bar restrictions in place. /neuman

&&

.pqr watches/warnings/advisories...

or...winter weather advisory until 10 am pst monday for cascade
     foothills in lane county-northern oregon cascade foothills.

     winter storm warning until 10 am pst monday for northern oregon
     cascades.

     winter storm warning until 4 pm pst monday for cascades in lane
     county.

wa...winter storm warning until 10 am pst monday for south
     washington cascades.

pz...small craft advisory until 10 pm pst monday for columbia river
     bar.

     small craft advisory until midnight pst monday night for
     coastal waters from cape shoalwater wa to florence or out 10 nm.

     hazardous seas warning until 2 pm pst monday for coastal waters
     from cape shoalwater wa to florence or from 10 to 60 nm.
&&

$$

www.weather.gov/portland

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