Scientific Forecaster Discussion
fxus66 kpqr 202207
Area forecast discussion
National Weather Service Portland or
206 PM PST Mon Nov 20 2017
Synopsis...wet and unsettled weather will continue this week. A cold
front has mostly moved south and east across the forecast area of
southwest Washington and northwest Oregon this afternoon. This
frontal boundary will lift north as a warm front tonight and Tuesday
with some windy conditions, especially near the coast, and more rain.
A trailing cold front will linger over the forecast area, especially
the coast and the north interior, Tuesday night and Wednesday for
more rain. Snow levels in the Cascades will remain relatively high.
The next cold front sweeps through on Thanksgiving with snow levels
in the Cascades lowering some Thursday afternoon and Friday. Look for
some lingering showers Friday before the next system arrives on the
Short term...tonight through Thursday...the main cold front that
came onshore over night and has mostly moved east of the Cascades and
south of the forecast area this afternoon, and the precipitation has
decreased to some showers. The models indicate the showers will
further decrease this afternoon and evening. Snow levels remain high
in the Cascades.
The frontal boundary continues to be forecast to lift back to the
north tonight and Tuesday as a significant warm front. This warm
front will have a good dose of rain with it, maintain the high snow
levels in the Cascades, increase east winds through the Columbia
River gorge, and increase south to southeast winds along the coast.
This is not a great pattern to get strong winds inland, though it
could get pretty windy near the beaches and headlands during the day
on Tuesday behind or south of the warm front. High winds are marginal
but possible. Looking at the vertical structure and magnitude of the
winds suggests that the best chance of seeing significant winds along
the coast will be 18z Tue-00z Wed.
While the warm front will tend to hang around near or just to our
north Tuesday night and Wednesday, a trailing cold frontal boundary
will then hang around the area Tuesday night and Wednesday for some
rain continuing. The models indicate that the amounts will be
heaviest over the northern mountains on Tuesday night, otherwise the
amounts will tend to be less than last night and those expected
through Tuesday. Snow levels will remain high.
The next cold front will approach the coast later Wednesday night and
move through southwest Washington and northwest Oregon on
Thanksgiving, pushing this whole mild moist air mass eastward in the
afternoon. Look for the precipitation to turn to showers from the
west Thursday afternoon with a dip in the snow levels Thursday
afternoon and evening, though snow levels will probably stay above
the passes Thanksgiving.
Total rainfall amounts through Thursday could reach 4-6 inches at the
coast and the mountains (heaviest north) and 0.67-1.50 in the
valleys. The Grays River at Rosburg did reach flood stage early this
morning and has crested and will need to be watched this week, but no
other rivers are expected to reach flood stage. In general, the
rainfall through the next few days is not expected to cause flooding
other than some possible localized urban flooding should leaves clog
storm drains, though area rivers and streams will likely continue to
see some sharp rises at times this week. Tolleson
Long term...Thursday night through Monday...we will be transitioning
to showers by Thursday night, which will be diminishing Friday. The
models keep speeding up the next system, which may arrive by
Saturday, and then may linger into Sunday. The next system is
expected Monday. After a brief drop in snow levels Friday mainly in
the north part of the forecast area, snow levels rise gain
significantly Saturday before dropping a bit again Sunday. May get a
brief rise in snow levels again Sunday night into early Monday at the
leading edge of the next system. Overall, the unsettled weather
pattern continues. Bishop/Tolleson
Aviation...tonight's front is hovering down just south of eug this
afternoon, with cloud decks breaking up and predominantly VFR
conditions across the area this afternoon. As the front makes its way
back northward tonight, expect MVFR/IFR cigs to return overnight,
with rain spreading back over the area. These conditions will persist
through at least Tuesday afternoon. Will see increasing southerly
winds on the coast Tuesday afternoon, with gusts up to 40 to 45 mph
probable at coastal terminals between 21z-03z.
Kpdx and approaches...VFR conditions this afternoon will continue
through this evening. Rain moves back in around 09z overnight,
bringing cigs and/or vis down to predominantly MVFR, continuing
through much of Tuesday. -McCoy
Marine...winds have dropped below 20 kt and seas are gradually
subsiding today. The next system to watch is the front that moved
through last night which has stalled just south of our area. This
front will become the warm front associated with our next system
which will move through tonight, bringing winds back up over our
waters, with southerly gale force winds out past 10 nm from the
coast. Seas will likely build back up into the mid-to-upper teens
with this system, with higher seas out past 10 nm where the stronger
winds are located. Winds will peak midday Tuesday as this wave moves
across the waters, with seas peaking Tuesday night. Then, we should
see winds and seas subside through Wednesday morning.
We remain in an unsettled pattern with a series of systems moving
south to north offshore Wednesday and Thursday, bringing additional
chances for gale force winds in our outer waters beyond 10 nm from
the coast. This will keep seas up into the low-to-mid teens through
Thursday. May get a bit of a break on Friday, then another system
moves up the coast this weekend. -McCoy
Pz...Gale Warning from 4 am Tuesday to 3 am PST Wednesday for waters
from Cape Shoalwater Washington to Cascade Head or from 10 to 60
Small Craft Advisory for hazardous seas until 4 PM PST this
afternoon for coastal waters from Cape Shoalwater Washington to
Florence or out 60 nm.
Small Craft Advisory for winds from 2 am Tuesday to 3 am PST
Wednesday for coastal waters from Cape Shoalwater Washington to
Cascade Head or out 10 nm.
Gale Warning from midnight tonight to 3 am PST Wednesday for
waters from Cascade Head to Florence or from 10 to 60 nm.
Small Craft Advisory for winds from midnight tonight to 3 am
PST Wednesday for coastal waters from Cascade Head to
Florence or out 10 nm.
Small Craft Advisory for rough Columbia River bar until 4 PM
PST this afternoon.
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