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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
856 am pst mon jan 27 2020

updated aviation/marine sections

.synopsis...rain and mountain snow continues today and tonight. this
as a warm front lifts north across the region today, followed by a
cold front tonight. showery on tuesday. then pattern repeats on wed,
with rain increasing. unsettled weather continues into the weekend.
but, still have hope early next week for a dry day, or maybe even
two. but, does appear will be trending to cooler temperatures.
&&

.short term...monday through wednesday...not much in way of change.
weather this morning is rather benign, with variable clouds and
patchy fog, along with a few showers. but, that will change as this
morning progresses.

a new deepening low pres area well offshore will be our star today
into tonight, as it deepens and moves northeast towards vancouver
island over the next 24 hours. this low will maneuvers fronts across
the region. first, will see the frontal boundary over southwestern
oregon will lift north across western oregon today, with rain
increasing by mid to late morning. isentropic lifting increasing
dramatically across area between 15z and 18z (7 and 10 am) today, so
gives good support for increasing rain at that time. models maintain
plume of moisture being pulled up behind the warm front, with gfs
showing 1.0 to 1.2 inch precipitable water aimed at the coast, and
remains in place just as the cold front approaches from the west this
evening. that cold front will likely move onshore between 05z and 07z
(9 pm to 11 pm). that does not give much time for precipitation to
decrease along the coast. so, will see moderate to heavy rainfall
over the willapa hills and coast range, and coastal lowlands this
afternoon into this evening, with 1 to 3 inches of rain likely.
farther inland, somewhat less rainfall, with 0.50 to 1.00 inch for
interior lowlands and 1 to 2 inches for the cascades.

all this will be problematic for rivers in those areas, primarily
those draining the willapa hills. with the anticipated rainfall, will
see strong rises on coastal rivers, but most will stay below flood
stage. however, the grays may get close to flood stage later mon
night into tue am, as may other rivers draining the willapa hills.
so, will maintain flood watch for that area tonight into tue.

high up, snow levels will start out near 4000 feet this am, but
rising to 5000 to 5500 feet behind the warm front this afternoon.
will get decent shot of snow for the higher terrain, with generally 6
to 10 inches expected in south wa and north or cascades, and bit less
for lane county. snow levels drop back to 4000 to 4500 feet later
tonight into tue, with a repeat of snow accumulations. so, will post
winter weather advisories for the cascades, generally above 4500 feet
in s wash, and above 5000 feet in n ore cascades for today through
tue am.

models insist on rain transition to showers around or just after
midnight tonight across the region. the parent low that moved to off
vancouver island tonight will approach later tonight and tue am. air
mass will be unstable enough for some threat of thunderstorms tonight
through tue am, at which point the low will be weakening as it slows
its progress to the coast.

showers decreasing later tue afternoon into tue evening. can not
completely remove all mention of showers, but they will be rather hit
and miss by later tue evening. then act iii, as another strong,
rather moist front arrives on wed. will trend to increasing pops late
tue night into early wed, with rain most of the day on wed. this
system will be accompanied by another moist atmospheric plume, with
precipitable water values of 1.1 to 1.2 inch feeding into the frontal
zone. like today, will see moderate to heavy rain along the coast and
into the nearby higher terrain for wed. will have to close watch
coastal rivers again, as will likely see strong rises again at some
point during the day.      /rockey

.long term...wednesday night through sunday...models and
their ensembles are in good agreement that a positively tilted
shortwave ridge will push eastward into the rocky mountain states
during the middle part of next week. this will result in
increasingly zonal flow spreading across the region during the
latter half of the week. it appears likely a few showers will linger
across the region wednesday night behind a front that will pass
through the region earlier on wednesday. precipitation then appears
likely to become more focused along a warm front lifting
northeastward across the northeast pacific late thursday into early
friday. more uncertainty begins to creep into the forecast late
friday into early saturday as there is a fairly even split among
models and their ensembles on whether or not precipitation will lift
far enough north of the region to keep the area dry. as a result, a
blend of model guidance puts pops near climatology during this
period. what appears more certain is that temperatures will likely
remain above average and snow levels will likely be above the
cascade passes during this time.

it should be noted that whenever the front drops southward over the
weekend, cooler temperatures will likely push back into the region
with snow levels lowering below the cascade passes. have kept the
cooling out towards day 7 rather modest at this point given model
and ensemble spread, though.       /neuman
&&

.aviation...wide range of flight conditions this morning, with
the predominant mix being mvfr and vfr. expect to see mainly vfr
through 20z and then an increase in mvfr from the southwest as
the next warm front spreads into the area. will likely see areas
of ifr develop along the coast this afternoon. flight conditions
to remain ifr to mvfr late this afternoon through tue morning.
gusty south wind develops along the coast by early afternoon with
peak gusts to 45 kt. inland gusts inthe 20-25 kt range. there may
be a brief respite in the wind overnight, but models suggest a
secondary surge tue morning.

kpdx and approaches...expect predominant vfr through early
afternoon, but there will areas of mvfr along western approaches,
specifically the tualatin river valley. conditions lower into
mvfr 20-22z and remain there through tue morning. southerly wind
gusts 20-25 kts expected roughly 28/00z-07z. weishaar

&&

.marine...minimal changes to current forecast. a developing
complex of surface low centers will approach the pacnw coast
today from out near 43n, 145w. by late this afternoon, the
nearest lobe of the complex will have advanced to near 130w,
sending a warm front across the waters. pressure gradients will
be very tight with the low center in the low 990s and higher
pressure over land in the mid 1010s. as such, feel this system
will present a notably stronger gale threat today and this
evening than the last couple systems. do expect frequent gusts
35-40 kt and sporadic 40-45 kt gusts early this evening closer to
shore. however, there is some uncertainty as the overall warm
frontal nature of the system will have a tendency to keep the
higher winds lifted and less likely to reach the surface.
however, the best chance again for those higher gusts will be
this evening as rain turns back to showers and possible tstms.
seas, already in the lower teens, will notch toward the 15-18 ft
range this evening as winds peak. highest seas will remain closer
to shore and south of tillamook bay.

models continue to struggle with how to handle that cluster of
lows as the approach the shore around daybreak tuesday. the 12z
model runs have come into a little better agreement regarding the
central surface low pres 12z tue. there was up to an 11 mb
difference in prior runs, but the 12z runs seem to have converged
on a central pres around 995 mb. the westerly bent back occlusion
rotates into the area late tonight, with possible 35 kt gusts
over pzz255 and pzz275. may need to extend the gale warning for
those zones, but will make that decision for the afternoon
forecast.

tuesday night through early wednesday brings a break in the
action. although, wednesday will see possible gales and seas in
the upper teens as a 955mb low in the northern gulf of alaska
sends another frontal system across the waters by wednesday
afternoon. models all agree on the notion this will occur but are
very different on the strength of the features. thursday may
present somewhat of a break with gusts "only" in the 20-25 kt
range diminishing to the lower teens by nightfall. models then
continue to diverge further heading into the weekend, albeit with
a steady stream of wind concerns through early next week. seas
do not appear likely to fall below 10 feet for any prolonged
period in the near future. weishaar/jbonk

&&

.pqr watches/warnings/advisories...
or...winter weather advisory until noon pst tuesday for cascades in
     lane county-northern oregon cascades.

wa...flood watch from 4 pm pst this afternoon through tuesday
     afternoon for south washington coast-willapa hills.

     winter weather advisory until noon pst tuesday for south
     washington cascades.

pz...small craft advisory until 9 am pst this morning for coastal
     waters from cape shoalwater wa to florence or out 60 nm.

     gale warning until 10 pm pst this evening for coastal waters
     from cape shoalwater wa to florence or out 60 nm.

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

&&


$$

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

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