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

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Area Forecast Discussion
National Weather Service Portland, OR or
331 pm pst tue jan 26 2021


.synopsis...a dynamic occluded front continues to push north from the
pacific bringing mixed precipitation and snowfall to the area. this
front will move inland through the evening tonight and weaken through
the morning on wednesday. expecting more showery conditions wednesday
through thursday before a weak ridge attempts to build in behind it.
potential for a bit more "active" weather over the weekend.

&&

.short term...tonight through thursday night...quite an active
afternoon as a strong occluded front pushes northward from the
pacific. what started off as rain along the coast became a rain snow
mix for a few hours. most coastal areas have turned back to rain and
will continue to stay there through the evening. as we look east, the
coast range was the first to really get a good amount of accumulating
snow and will continue to do so for a few more areas. the snow
accumulations will be highest above 500 ft along the coast range
where they could see 2 to 4 inches and possibly higher amounts above
800 ft. shifting slightly lower, around 200-500 ft, accumulations
will likely stay below 2 inches. could also see slight snow
accumulation on roadways.

the willamette valley was a bit of a surprise this afternoon as the
snow arrived a bit earlier and heavier than expected. this was mainly
due to the evaporative cooling that the higher precipitation rates
produced. areas around corvallis saw temperatures drop from 37
degrees to near freezing in about an hour even. because of the
cooling and dry air at the surface, more snow was able to reach the
surface at a quicker rate than expected. local webcams around the
area are showing anywhere from 0.5 to 1 inch of snow west of i-5 in
the central willamette valley, and more snow accumulation is
possible. shifting northward, a rain snow mix is more widespread. the
west hills of portland, western washington county and northern clark
county are experiencing more consistent snow with higher
accumulations. while the inner portland/vancouver metro continues
with the rain/snow mix with struggling accumulations. easterly winds
through the columbia river gorge has formed a shallow layer of drier
air which has caused the precipitation to evaporate before reaching
the surface. hence why areas around the columbia river were the last
areas to see the snow starting to fall.

these snow conditions will persist for the next few hours with
accumulations highest along the coast range, cascades foothills and
cascades range. most locations within the forecast area are under a
winter weather advisory through wednesday early morning. snow should
transition to rain and become showery in the post frontal environment
as precipitation rates lighten up later this evening. the exact
timing of this change is difficult to forecast as it will greatly
depend on whether or not the front will be reinvigorated by any post
frontal lift. another challenge that may occur during the overnight
hours is the chance for the freezing of any melted snow or rain from
this afternoon. in areas with more accumulating snow, around 2 inches
or more, there tends to be an insulating effect which will keep those
areas cooler than those without much accumulation. combine this with
continued easterly winds and the residual cool air, there is a chance
that freezing could occur overnight into the early morning hours on
wednesday...potentially impacting the morning commute. for areas that
have less snow cover, the ground likely will be able to radiate heat
and assist in keeping any freezing at bay. there are so many factors
that go into this chance for refreezing so there is not a ton of
confidence so will just say that there is a chance.

showers will persist through wednesday in the post frontal
environment. snow will remain concentrated to the coast and cascades
ranges above 1000-1500 ft or so, while elsewhere will be rainy. not
expecting too much accumulation of either rain or snow.
precipitation will continue to lighten through wednesday evening into
thursday as all residual shortwaves move out of the area and an area
of very weak high pressure attempts to develop on thursday night.
-muessle


.long term...friday through monday...a shortwave upper ridge may
provide a brief break in precipitation friday morning, but the next
front will bring another chance for rain and snow (above 2000 feet)
friday afternoon or evening through saturday. a complex low over the
pacific supports the chance for waves to either bring a series of
fronts across the area or slow the movement of the saturday front
for potentially a prolonged period of wet weather saturday through
tuesday. the gefs and ecmwf integrated vapor transport (ivt)
forecast is trending towards a possible weak atmospheric river (ar)
event. there is potential for the cascades to have a few days of
accumulating snow as snow levels are expected to roughly be 2500 to
3500 feet during this wet period. ~tj
&&

.aviation...front offshore continues to spread rain across
region, with inland low elevation snow. widespread mvfr, with
areas of ifr where snow is occurring. do think snow will trend
to decrease for the lowlands after 03z to 04z. afterwards, will
trend to showery precipitation, with snow levels sitting closer
to 1000 feet. even so, will maintain widespread mvfr overnight.
showers decreasing overnight, with mix of mvfr to lower vfr after
12z, with not much change through wed am.

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

kpdx and approaches...cigs will quickly drop to mvfr as the
precipitation spreads across region through 23z. air mass such
that will see mix of rain/snow, but will have a period of just
snow at times between 23z and 04z. overall, mvfr with occasional
ifr during that time. again, think may see wet dusting to half
inch on grassy areas, but any snow that does fall will melt this
evening, with no danger of freezing overnight. overnight will
maintain mvfr, with decreasing showers.   /rockey

&&

.marine...broad area of low pres over the offshore waters
continues to slowly drop southeastward tonight. front now pushing
closer to shore, with southeasterly gales still on the waters.
overall, strongest winds are just offshore, with winds gusting 35
to 45 kt on the outer waters. closer to shore, gusts mostly 30 to
35 kt. winds will ease this evening, and stay in the 15 to 20 kt
range overnight into wed. will keep current gale warning through
7 pm, but will need small craft advisories afterwards to cover
the gusty winds and seas that will stay in the mid-teens.

a rebuilding westerly swell late tonight are expected to keep seas a
little above 10 ft through wednesday night. a broad area of low
pressure is expected to linger past mid week over the coastal
waters, and may bring some wind gusts up into the range of 20 to 25
kt wednesday and wednesday night. another chance for small craft
level winds comes with a front friday night.   /rockey

&&

.pqr watches/warnings/advisories...
or...winter weather advisory until 7 am pst wednesday for cascade
     foothills in lane county-cascades in lane county-central
     columbia river gorge-northern oregon cascade foothills-
     northern oregon cascades-upper hood river valley.

     winter weather advisory until 4 am pst wednesday for greater
     portland metro area-western columbia river gorge.

     winter weather advisory until 4 am pst wednesday for central
     coast range of western oregon-central willamette valley-
     coast range of northwest oregon-south willamette valley.

wa...winter weather advisory until 7 am pst wednesday for central
     columbia river gorge-south washington cascade foothills-
     south washington cascades.

     winter weather advisory until 4 am pst wednesday for greater
     vancouver area-western columbia river gorge.

     winter weather advisory until 4 am pst wednesday for willapa
     hills.

pz...gale warning until 7 pm pst this evening for coastal waters
     from cape shoalwater wa to florence or out 60 nm.

     small craft advisory until 6 pm pst wednesday for columbia
     river bar.

&&

$$

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