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

fxus66 kpqr 251608

Area Forecast Discussion
National Weather Service Portland, OR oregon
908 am pdt tue oct 25 2016

.synopsis...deep low pressure below 980 mb centered well off southern
vancouver island and the northern washington coast will gradually
weaken and move north through wednesday. a second low closer to 990
mb is forecast to move north off the oregon coast late tonight and
wednesday for gusty coastal winds and more rain at times before
weakening as it makes landfall on vancouver island wednesday night.
another disturbance is expected thursday. another low is expected to
send surges of moisture into the forecast area this weekend.

.update...shower bands rotating around a large low offshore of the
british columbia coast will continue showers across nw oregon and sw
washington this morning. a line of thunderstorms were embedded in
these showers over the waters off of south washington and north
oregon early this morning. radar showed some rotation with these
cells as they moved north into the north washington waters. these
storms have mostly stayed over the waters, but there have been a few
isolated thunderstorms making it to the immediate coast, before
quickly weakening. satellite and radar imagery shows another weaker
line of thunderstorms approaching the central oregon waters, and have
added isolated thunderstorms for the central oregon coast and coastal
waters through this morning.

satellite imagery shows the next low developing offshore of north
california. this low has a lot of moisture with it as satellite
derived precipitable water shows a bullseye of 2.2 inch precipitable
water values near the forming low center. there is an extended swath
of 1.5 inch precipitable waters just south of the forming low. gfs
modeled precipitable water is forecasting the general moisture around
1.5 inches, but does not show the locally higher amounts around the
low center. we will watch these values as the low continues to
develop and moves towards the pacific northwest this afternoon.

the observed moisture on satellite has increased the forecast
confidence that this low will produce a warm front that will move
across nw oregon and sw washington overnight tonight into early wed
morning. the front is rather quick moving which will prevent the
rainfall totals from being excessively high. however with the high
moisture content, expect the rain to be heavy at times, and high rain
rates may challenge small streams and drains, especially if they are
clogged with leaves. the highest rain totals will be over the higher
terrain of the coast range, and modeled 850mb south winds around 70
kt will likely enhance orographic lift. can expect around 1 to 2
inches of rain for the coast range, and washington cascades tonight
through wed morning, and 0.5 to 0.75 inch elsewhere.

the winds will gust along the immediate coast wednesday morning
impacting the beaches and headland and higher terrain of the coast
range the most with gusts up to 50 mph. east winds will increase in
the gorge tonight where gusts around 45 mph can be expected through
wed morning. east portland areas near the columbia gorge entrance
will also have breezy east winds tonight and wed morning with gusts
around 35 or 40 mph. tj

previous short term from 403 am this through
thursday...a deep low likely below 980 mb was centered off vancouver
island and the north washington coast outside 130w early this morning
and will slowly weaken as it moves northwest into the gulf of alaska
today and tonight. the associated cold front moved east of the
forecast area overnight and we are under south to southwest flow
aloft with a few showers around. the best coverage of showers early
this morning has been over the coastal waters and near the coast, and
the langley hill national weather service doppler radar showed
several storms earlier with rotating updrafts for which we issued
special marine warnings. that activity seems to have eased a bit now.
will keep a chance of thunder along the coast through the morning per
lifted index forecasts.

there is another comma cloud beginning to develop this morning out
around 37n/138w that the models develop into a low around 990 mb that
moves north along the oregon coast just inside 130w late tonight and
wednesday. the coastal gradient remains rather easterly again with
this storm and that may prevent high winds from developing, but still
expect some winds along the coast again. the strongest winds will be
over the coastal waters. the associated moist warm front with pws
pushing 1.5 inches accompanied by 850 mb inflow winds of 60 to 70 kt
will lift north through our forecast area late tonight and wednesday
morning with pretty substantial rains. the rains will not likely last
long enough for any river flooding, though local ponding of water is

the surface low weakens as it makes landfall into vancouver island
wednesday night. the associated cold front lingers over southwest
washington and northwest oregon into early thursday for decent rain
continuing before letting up on thursday. one more upper level
disturbance will move through on thursday and finally push the front
east of the forecast area later in the day. tolleson

.long changes. previous discussion follows...
thursday night through monday...wet weather pattern looks to continue
into this weekend, with another trough dropping out of the gulf of
alaska thursday into friday. may get a brief break from the rain
friday morning as shortwave ridging builds up ahead of the next
surface low that comes up from the southwest. this low looks fairly
weak, bottoming out in the high 990s to right around 1000 mb. heavier
rain will impact southwest oregon, but should be more moderate as it
moves farther north into northwest oregon and southwest washington.
showers should linger across the area saturday night through sunday
morning before another weak system comes up the same track as the
last low, along the track of the south side of the upper-level trough
sitting off the coast of washington and oregon. this one looks fairly
weak as well, only bringing moderate rainfall to our area sunday
evening through monday morning. this second surface low is more
associated with the upper-level trough, which shifts onshore sunday
night into monday, though another upper-level trough appears to come
in and take its place off the coast of washington and oregon for
on-and-off rainy weather to continue into early next week. -mccoy

.aviation...predominately vfr today and tonight. scattered showers
will continue across the forecast area this morning, with isolated
thunderstorms possible along the coast mainly in the morning through
19z. another low pressure system will spread rain across the region
tonight, with brief period of mvfr cigs and vsbys possible. gusty
south to southeast winds possible through this afternoon.

kpdx and approaches...predominately vfr. isolated showers today,
with rain returning after 06z. gusty southeast winds possible
through 00z.


.marine...low pres center near 49n 133w will continue to weaken and
drift nw today. wind over the southern waters have generally
subsided below gale strength, so will drop the warning there with
the morning forecast. over the northern waters both buoy 46029 and
garibaldi still indicating gale force gusts, so that warning will be
allowed to continue through expiration midday. seas were down in the
upper teens this morning at 46029 and 46050, and should continue to
subside slowly today as both winds and sw swell diminish.

another weaker low will move north off the oregon and washington
coast late tonight through wed night, likely near 129w to 130w.
while not as intense, the low still appears strong enough to warrant
the gale watch for the outer waters wed. late in the week looks a
little calmer on the coastal waters with a weak frontal system
approaching the waters fri.


.pqr watches/warnings/advisories...
pz...gale watch from wednesday morning through wednesday evening for
     waters from cape shoalwater wa to florence or from 10 to
     60 nm.

     gale warning until noon pdt today for coastal waters from cape
     shoalwater wa to cascade head or out 60 nm.

     small craft advisory for rough columbia river bar until 6 am
     pdt wednesday.


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

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