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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
1014 am pst fri nov 15 2019

.synopsis...cold front has moved east of the cascades leaving
showers in it`s wake. showers will gradually taper off this
afternoon and evening. clouds break up later tonight which will
allow for pockets of fog to develop by early saturday morning. the
fog may be slow to lift into a low stratus deck for a few areas,
namely the south willamette valley. a weaker front on sunday will
mainly affect northern portions of the forecast area with another
chance for rain. more widespread rain is possible late monday and/or
tuesday as a low pressure system moves across the pacific northwest.

&&

.short term...today through sunday...morning update was sent earlier
mainly to reflect qpf details for the rest of the post-frontal
period through this evening. also changed zone wording to indicate
shower coverage vs. probability. snow levels remain 7000-8000 feet
and will see a slight bump up this morning before the deeper cooler
air arrives this afternoon. still, do not expect them to get much
below 5500 feet for the south washington/north oregon cascades and
6500 feet for the central oregon cascades by the time showers taper
off late this evening.

for the afternoon package, will be taking a closer look at fog
coverage for tonight as temperatures will not stray too far from
dew points this afternoon. this will make it fairly easy to saturate
the surface as clouds break up at times overnight. would not be
surprised if there is some local dense fog by daybreak saturday.
/jbonk


previous discussion from 248 am follows: as of 2 am pst this
morning, an approaching cold front had finally spread steady rain
onshore, with some areas of light rain beginning to develop over the
willamette valley. this front has been in no hurry to move onshore,
partially due to a split flow pattern that has developed along the
west coast. that said, this system will begin to accelerate eastward
over the coming hours as it begins to feel the influence of an 80-
100 kt streak within the north pacific jet stream. the left-front
quadrant of this jet streak will provide modest forcing to act on
total precipitable water values of around 1 inch, likely wringing
out 0.25 to 0.50" of rain along the coast and across much of sw
washington, and locally up to 1 inch in the higher terrain. the
willamette valley will likely receive less, especially west of
interstate 5 where some downsloping westerly flow will limit post-
frontal showers. as has been the case with our recent frontal
systems, snow levels should remain well above the cascade passes.

high pressure will build both at the surface and aloft tonight and
saturday, although upper level ridging will be somewhat flat. this
will keep the jet stream close enough to the pac nw to bring another
chance of rain to our northern zones sunday as the next shortwave
clips by to our north. again, snow levels look to remain well above
the cascade passes sunday.

renewed ground moisture from today`s rain will probably lead to areas
of valley fog the next couple nights and mornings, some of which may
be dense if higher clouds thin enough. fog, inversions, and a return
to unseasonably warm 850 mb temps will make temperature forecasting
tricky for the inland valleys saturday and potentially sunday, but
overall temps should be within a few degrees of normal if not
slightly on the warm side of normal with highs generally in the 50s
for the lowlands.  weagle

.long term...sunday night through thursday...no changes.
previous discussion follows...medium range models are in fairly good
agreement with the southern remnants of the upper ridge
reestablishing across the region sunday night and most of monday. a
well established upper low starts the period near 45n, 150w then
slides eastward to near 130w by monday afternoon. the gfs is the
coldest and strongest of the models and brings rain to the north
coastal areas by mid-day monday while other models are slightly
slower and warmer. they all agree the bulk of the rain shield will
cross monday evening through early tuesday morning with perhaps up
to 1/2" pf qpf possible for favored portions of the coast range and
cascades. by this time, however, even the colder gfs lifts snow
levels to well above the passes.

the upper low moves inland tuesday, but a trailing vort max drops
south along the western flank of the low and forms a new low as it
continues diving south along the coastline and into california. this
will keel some chance of rain continuing through most of the day
tuesday and tuesday evening. the differing details of the models
will ultimately determine just how much rain fall and how long it
will fall, but amounts do not seem to be all that impressive once
the initial low passes by monday night.

the broad model agreement continue well into the long term period as
they all show a fairly high amplitude ridge building offshore by
early wednesday. this will serve to keep the region dry through at
least thursday. /jbonk

&&

.aviation...front over the coastal waters is expected to make
landfall around 12z and over the interior lowlands 16-18z. at the
coast - expect rain with mvfr to ifr conditions to improve to
mainly mvfr 16-18z and possibly vfr after 20-22z as some guidance
indicate. for now will hold to mvfr with low level moisture over
the waters and onshore flow convergence. for inland areas - cigs
have lifted to mvfr with cigs around 2000-2500 ft and local vis
3-5 sm. as rain increases should see more widespread reduction in
vis and cigs down to 1500-2000 ft. also can`t rule out a few
hours of ifr. think the best chances for ifr will be in the
15-18z time frame as the front moves through. will see gradual
improvement behind the front with vfr likely around 00z sat, but
areas south of ksle may not see much improvement due to little
mixing there. mvfr become more widespread after 06z sat as the
air mass stabilizes.

kpdx and approaches...mvfr cigs around 2000-2500 ft filling in
the area just ahead of the front. should see cigs 1500-2000 ft as
the front moves through. also can`t rule out ifr conditions.
think 15-18z is most likely period for ifr conditions. vfr
conditions should return around 00z, then lower again to mvfr
after 06z sat. /26

&&

.marine...a front will move ashore this morning with winds easing
below small craft advisory. models show a bit of a coastal jet so
will probably see gust 30-35 kt briefly. seas will be in the 11
to 13 feet for the outer waters, and 10 to 12 feet for the inner
waters through tonight then drop below 10 ft for the inner
waters sat. another front will arrive saturday,and could bring
small craft advisory winds back into our waters through the
weekend. /26 /42

&&

.pqr watches/warnings/advisories...
or...none.
wa...none.
pz...small craft advisory until 4 pm pst saturday for coastal waters
     from cape shoalwater wa to florence or from 10 to 60 nm.

     small craft advisory until 10 pm pst this evening for coastal
     waters from cape shoalwater wa to florence or out 10 nm.

     small craft advisory until 10 am pst this morning for columbia
     river bar.

     small craft advisory from 4 pm this afternoon to 10 pm pst this
     evening for columbia river bar.

&&

$$

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this discussion is for northwest oregon and southwest washington
from the cascade crest to 60 nautical miles offshore. this area is
commonly referred to as the forecast area.

Information courtesy of the National Weather Service - NWS Portland...
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