Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
258 am PST Wednesday Dec 11 2013
Synopsis...dry conditions expected today and tonight with an upper
level ridge near the coast today sliding slowly inland tonight...
with areas of rather persistent valley fog and freezing fog into
Thursday. The air mass will slowly moderate through Thursday and
Friday...first at middle levels and eventually near the surface. The
next system is stronger and wetter and will reach the coast middle day
Thursday and inland later Thursday and Thursday night. The
precipitation inland will likely start as a wintry mix and
eventually transition to mainly rain late Thursday or Thursday
Short term...today through Friday...an upper ridge will be over
southwest Washington and northwest Oregon today...slowly sliding
east tonight and Thursday morning. This will bring a period of dry
weather. It will also bring an inversion with warmer air aloft moving
into the coastal mountains and Cascade foothills...with fog or
freezing fog and low clouds in the valleys. Easterly winds will
increase through The Gorge today...clearing out the fog near The
Gorge. Areas away from The Gorge such as the south and central
Willamette Valley may have a tough time breaking out today...and if
they do at all...will likely see the fog and freezing fog reform
early tonight. The Tualatin valley will be a tough call on whether
the east winds will be strong enough to clear that area out. If the
fog does persist...those areas may struggle to reach freezing today.
Have issued some dense fog advisories for this morning as outlined
The next system still looks on tap for Thursday and Thursday night.
Model timing still is a bit slow...with the north coast seeing
precipitation around middle day and inland later in the day and Thursday
night. We should still see a lot of fog and freezing fog in the
valleys in the morning...and this should make it cold to start the
day. The fog will likely again be slow to break up...and this should
aid the chance of seeing some freezing rain inland with the onset of
the precipitation. The main front moves through Thursday night and
should mix out most areas. There will be an initial light easterly
drift to the winds...but they should turn more southerly down the
valley and the period of winter precipitation in most areas is
probably not too extensive. The exception could be The Gorge...which
may take until late Thursday night or Friday morning for westerly
winds to break through and mix out the area. Will continue the
current Special Weather Statement for this episode.
We should still see some rain or showers on Friday in onshore flow
though the precipitation should decrease through the day. We may
finally see more areas reach the 40s on Friday.
The Thursday and Friday system should also produce some snow in the
Cascades...but mainly up at the ski resorts. Tolleson
Long term...no changes. Previous discussion follows...
Friday night through Monday...upper level ridge pushes back over the
Pacific northwest Friday night. Upper flow becomes zonal Saturday as models
bring a decaying front across the pacnw Saturday afternoon. Sunday
the upper high rebuilds off the Southern California coast...for a
return to northwest flow aloft. There is indication that shallow
moisture will continue to stream into the area over the ridge...but
have low confidence that any of it will survive to bring precipitation to
the region. Burgess
Aviation...variable high clouds today with light offshore flow.
Widespread IFR in fog and stratus...with tops 1000 to 1500 feet...
extending from Cowlitz valley to Portland and through Willamette
Valley. Local studies indicate this fog/stratus will burn out between
19z and 22z. Will have pockets of dense fog through 18z. Less fog
tonight as have bit more in way of offshore winds. But fog will
reform S of Portland and north of Kelso...with VFR conditions elsewhere.
Will have increasing highs clouds overnight.
Kpdx and approaches...IFR stratus/fog persists this am... with
gradual improvement of visible to MVFR after 17z. Stratus/fog will burn
burn off around 20z. VFR afterwards with light east wind. Rockey.
Marine...tranquil weather continues through tonight. High pressure over
Pacific northwest...with light east to southeast winds. Seas holding near 3 feet. Next front
will arrive on Thursday...and push onshore late Thursday. Gradients not all
that impressive. Southeast winds will become S and pick up on Thursday... with 20
to 30 knots by afternoon. Gradient may be enough to pop a few gust to 35
knots...but overall not enough to support and gale watch or warning at
this time. Next shift or two can continue to monitor models trends
for gale potential. Seas will build as the winds pick up...with 10 to
12 feet seas later Thursday and Thursday night.
High pressure builds over the NE Pacific on Friday...with west to SW winds 15 knots.
Seas will drop back to 6 to 8 feet. May see another swell train arrive
on sun. Will keep swell at around 10 feet on sun.
or...dense fog advisory until noon PST today for greater Portland
metropolitan area-lower Columbia-south Willamette Valley.
Washington...dense fog advisory until noon PST today for Greater Vancouver
area-I-5 corridor in Cowlitz County.
More weather information online at..
Interact with US via social media
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.