Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus66 kpqr 201101 

Area forecast discussion
National Weather Service Portland or
255 am PST Wed Nov 20 2019

Synopsis...high pressure over the region will result in benign
weather through the first half of the weekend before an increasingly
active and stormy weather pattern develops next week.


Short through Saturday...water vapor satellite imagery
early this morning reveals a shortwave ridge over the northeast
Pacific and a closed low pressure over California. Models are in good
agreement the shortwave ridge will slowly Bend over and shift across
the Pacific northwest over the next 48 hours. This will bring a
multi-day stretch of dry weather to the region.

Offshore pressure gradients will build later today into Thursday,
which should result in increasing easterly winds through the Columbia
River gorge. In addition, there should be enough of a northerly
pressure gradient across the region that air stagnation concerns
should be limited to nonexistent across the area today into Thursday.

A weak and splitting shortwave trough will push towards the region
Thursday into Friday. This upper level storm system will drag a dying
low level front towards the region Thursday night into Friday. Model
and ensemble guidance continue to suggest it will fall apart enough
before arriving to maintain a dry forecast. The main impact from this
storm system is that it will likely reduce offshore pressure
gradients enough that fog coverage should expand Friday and Saturday
mornings across the area. Otherwise, expect high temperatures right
near average for the date with low temperatures near to below
freezing at night for many valley locations through Saturday. /Neuman

Long term...Saturday night through Wednesday...models and their
ensembles are in fair agreement a shortwave ridge will Bend over the
Pacific northwest and open the door for an increasingly zonal and
active weather pattern for the Pacific northwest next week.
Conditions should start off dry across the area Saturday evening
before a dying front drop southeastward across the area Saturday
night into Sunday. Some amplitude and timing differences still exist
during the Saturday night and Sunday timeframe so pops have generally
been held into the chance to likely categories for now.

Models then generally agree a strong upper level jet will take aim at
the Pacific northwest early next week. The operational GFS and ec
suggest a weak surface low pressure will develop and track towards
the Pacific northwest. This would likely result in a wet and
potentially cool pattern with plenty of snow across the Cascades
Tuesday into Wednesday. Meanwhile, the Gem suggests a much stronger
surface low pressure will track towards the region, which would
result in a considerably milder, windier and somewhat wet pattern for
the region. Considering the spread in the gefs and ecs ensemble
systems, a variety of scenarios appear on The Table Tuesday into
Wednesday so have opted towards trending the forecast towards a
middle of the Road scenario as output by nbm guidance. /Neuman


Aviation...the predominate cig will be VFR except along the
southern Willamette Valley and areas along the coast where
conditions will vary between all cig levels; similar to the last
few nights. IFR stratus and reduced visibility due to fog are
present in areas around kast as well as ktmk. With many inland
areas still under MVFR stratus (1000 to 2000 ft agl), widespread
fog is not expected. If it does form, it will likely be in areas
prone to fog like khio which have been clear overnight. High
pressure building in overnight through Wed will keep skies VFR
above 4000 ft above ground level. With that being said, clearing skies through
the day with residual moisture may cause some frost to form in
the early morning after 12z Wed and again after 10z Thu. This
frost is likely to be focused through the Willamette Valley.
Winds will begin to turn offshore around 18z Wed and continue
through the forecast period. With an increased pressure gradient
between kttd and kdls, gusty winds are possible through the
Columbia River gorge after 06z Thu.

Kpdx and approaches...VFR ceilings will dominate through Wed with
some brief periods of lower MVFR cigs possible early Wed morning
after 12z. Winds are becoming offshore and will continue to be
through Thu. East winds will increase around 20z Wed where they will
persist until late Wed night. Frost is possible after 12z Wed and
after 10z Thu. Patchy fog possible Thu morning. -Muessle

&& general, seas and winds will continue to ease
through morning hours. The Small Craft Advisory winds in the
central outer waters are expected to persist at around 10 to 15
kt gust 20 kt through late Wed. Seas will continue to fall below
11 ft early Thu morning which is when the Small Craft Advisory
is expected to expire. High pressure building over the waters
will cause conditions to transition winds to the 10 to 15 kt
range and seas around 6 ft.

The next system is expected to move over the waters Thu
afternoon. Over the last several days, this system has weakened
which leads to some lack of confidence in the track and
intensity. However, guidance is still forecasting seas to
increase quite drastically to 12 to 14 ft with a period of 15 to
18 seconds Fri night into Sat. Conditions will again ease on sun
as zonal flow takes hold. -Muessle


Pqr watches/warnings/advisories...
Pz...Small Craft Advisory until 10 am PST this morning for coastal
waters from Cape Shoalwater Washington to Florence or out 10
nm.Waters from Cape Shoalwater Washington to Cascade Head or from
10 to 60 nm.

Small Craft Advisory until 4 am PST Thursday for waters from
Cascade Head to Florence or from 10 to 60 nm.



Interact with US via social media:

National Weather Service Glossary of Abbreviations