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fxus66 kpqr 221650 
afdpqr

Area forecast discussion
National Weather Service Portland or
849 am PST Fri Nov 22 2019

Updated aviation section.

Synopsis...dry weather as a result of high pressure over the Pacific
northwest will give way to a series of fronts and low pressure
systems beginning this weekend and continuing through at least the
first half of next week. Holiday travelers should be prepared for
snow across the Cascades beginning Sunday night or Monday.



&&



Short term...today through Monday...water vapor satellite imagery
early this morning reveals an upper level low pressure spinning over
The Four Corners. The shortwave ridge that has been in place across
the Pacific northwest continues to be eroded as it flattens and
shifts into the northern Rocky Mountain states. A shortwave trough
sliding eastward into British Columbia is currently in the process of
splitting with a weak upper level closed low pressure beginning to
form off the Oregon coast. Models are in good agreement this feature
will slide south-southwestward and morph into another large closed
low pressure off the Southern California coast. The end result is
that our fairly benign weather pattern of late will more or less
continue through Saturday. Expect fog coverage, locally dense in
spots, to increase this morning and then again Saturday morning. Low
temperatures will continue to drop to near or below freezing with
high temperatures topping out near average for the date through
Saturday.

The weather pattern will begin to finally change late in the weekend
as a stronger shortwave trough slides eastward into British Columbia.
This will result in a trailing low level front to drop southeastward
into the area Saturday night into Sunday. Models and their ensembles
suggest rain is all but a given Saturday night or Sunday across our
northern zones with a good chance that even our southern zones will
experience a period of light rain Sunday. Trended pops upward, but
there still remains some slight timing differences between models
and their ensembles to keep pops out of the 90-100% range.

Models then suggest a strong jet approaching 200 kt will form across
the Gulf of Alaska late Sunday into early Monday. This jet will then
take aim at the Pacific northwest and result in a longwave trough
developing over the western US early next week. Operational models
suggest an embedded shortwave trough will dive southeastward across
the area late Sunday night into Monday. However, there are enough
timing and amplitude differences among various gefs and eps ensemble
members to keep pops in only the chance to likely categories for now
during this time period. Either way, with the flow increasingly
turning northwesterly, colder air will filter into the region and
allow snow levels to lower below the Cascade passes Sunday night
into Monday. As a result, anyone planning to travel across the
Cascade passes should be prepared for winter travel conditions
beginning Sunday night and Monday. /Neuman



Long term...Monday night through Thanksgiving day...few changes to
the long term as the spread among the latest operational model and
ensemble solutions suggest the large degree of uncertainty
highlighted in the previous discussion remains. /Neuman

See below...

Attention then turns to the low pressure system shown by many
models/ensembles rounding the base of said upper trough and moving
into the West Coast, mainly Tuesday. There are still enormous
differences between members regarding the evolution of this system,
with the range of landfall solutions extending from Vancouver Island
to south of San Francisco and solutions for the low's intensity
ranging from sub-960 mb to around 1000 mb as it moves onshore. Given
the cold air pushing down with the upper trough, and the potential
for the low to come onshore to the south of all or part of the
forecast area, this system will need to be watched for the potential
for low elevation snow north of the low. That said, no single
solution can be trusted (nor discounted) at this point, especially
given the variance between guidance. For now, we continued to trend
our forecast colder, with snow levels generally around 2000 feet
Tuesday then down to 1000-1500 feet by Wednesday. Longer range
guidance appears to be in decent agreement that the upper trough
Will Park over the pac northwest through Thanksgiving, with scattered
showers and possibly even a few flurries reaching down to the lowest
elevations. Weagle



&&



Aviation...clear and dry conditions are expected throughout the
day. Current fog conditions affecting kpdx and keug should
elevate and improve to MVFR conditions by 19z Fri and . Coastal
sites will stay VFR throughout the forecast as light drainage
winds keeps the area dry. High pressure influence will persist
throughout the day creating VFR conditions across the forecast
area. There is a weak shortwave that will track south along the
coast but no precipitation is expected. Weak onshore flow will
transition to an easterly pattern after around 03z Sat. Because
of clear skies and low winds through the day coupled with the
overall synoptic pattern, localized fog is likely by Saturday
morning.

Kpdx and approaches...fog conditions are expected to improve to
MVFR conditions by 22z. Expect VFR conditions through today with
winds turning from westerly to southeasterly. LIFR fog
conditions returning again Sat morning. -Bphillips



&&

Marine...long period 18 second swell will continue through Sat
night. While the period will ease slightly to around 15 seconds
on sun, seas should remain in the 11 to 13 ft range through sun.
On Mon night, a front associated with a strong North Pacific low,
will advance towards the waters. This low track however has a lot
of uncertainty with it due to a lack of model consistency between
each other and runs. One solution has the low tracking more
northward over the central Oregon coast while a second model
depicts the low moving over the southern Oregon waters near the
California border. Where this low moves will greatly impact
winds. At this time, forecast winds are increasing with speeds
near 15 to 20 kt with gusts to 30 kt late Tue through Wed. The
pattern will also impact seas, however they are expected to
remain near 11 to 13 ft. Precipitation is likely with this
system. -Muessle

&&

Pqr watches/warnings/advisories...
or...dense fog advisory until 10 am PST this morning for lower
Columbia.

Washington...dense fog advisory until 10 am PST this morning for I-5
corridor in Cowlitz County.

Pz...Small Craft Advisory until 4 PM PST Saturday for coastal waters
from Cape Shoalwater Washington to Florence or out 60 nm.

Small Craft Advisory until 4 am PST Saturday for Columbia River
bar.

&&



&&

Pqr watches/warnings/advisories...
or...dense fog advisory until 10 am PST this morning for lower
Columbia.

Washington...dense fog advisory until 10 am PST this morning for I-5
corridor in Cowlitz County.

Pz...Small Craft Advisory until 4 PM PST Saturday for coastal waters
from Cape Shoalwater Washington to Florence or out 60 nm.

Small Craft Advisory until 4 am PST Saturday for Columbia River
bar.

&&



&&



Pqr watches/warnings/advisories...
or...dense fog advisory until 10 am PST this morning for lower
Columbia.

Washington...dense fog advisory until 10 am PST this morning for I-5
corridor in Cowlitz County.

Pz...Small Craft Advisory until 4 PM PST Saturday for coastal waters
from Cape Shoalwater Washington to Florence or out 60 nm.

Small Craft Advisory until 4 am PST Saturday for Columbia River
bar.

&&



$$



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