Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
342 am PST Thursday Feb 11 2016
Synopsis...southwest Washington and northwest Oregon remain in the
southwest flow aloft between an upper ridge inland over eastern
Washington and Oregon and a low pressure system out near 140w. A
weak warm frontal boundary will lift north today...followed by the
associated cold front moving onshore tonight and through the
forecast area on Friday. Snow levels will drop down to pass
elevations Friday night as another disturbance moves through for
showers. Another warm front will move in late Saturday and Saturday
night for more rain and for some snow in the mountains...then linger
through Sunday and produce more rain while snow levels rise in the
Cascades. The warm front will move mostly north of the area Sunday
night and Monday. Another cold front will bring some rain early next
week before the main colder upper trough moves through middle to late
next week with falling snow levels in the mountains.
Short term...a frontal boundary from the weak system that moved
through Wednesday remained over southwest Washington and northwest
Oregon overnight...and is forecast to lift north as a warm front
today and early tonight. This will bring some areas of rain to
southwest Washington and northwest Oregon at times today into
tonight...especially along the coast and in the north interior areas.
Echoes have begun picking up off the north Oregon coast already early
this morning...and this may be the main boundary. Precipitation will
move north into western Washington today and this evening...but will
probably linger from about Portland north inland.
The associated cold front out around 135w this morning is forecast to
approach the coast tonight and move through in the inland areas in
the morning and early afternoon on Friday...and should be east of the
Cascades by 4 PM Friday. Snow levels will be well above the Cascade
passes for most of this event.
Snow levels fall to below the passes Friday night behind the front
and as a short wave moves through that will produce a decent shot of
showers Friday night an Saturday morning. Snow amounts look a little
below advisory amounts at this point.
This is forecast to be followed by a warm front that will approach
the coast late Saturday and be over the forecast area Saturday night
and Sunday. The models show two good waves moving along the warm
front during this time frame...one Saturday night and the other on
Sunday. Snow levels in the Cascades will start below the Cascade
passes Saturday night but likely rise well above the passes on
Sunday. The best chance of seeing advisory amounts would be Saturday
night before the snow level rises...especially in the north
Long term...no changes. Previous discussion follows...
Saturday night through Wednesday...the progressive weather pattern
will persist into next week. Models continue to show a front moving
across the Pacific northwest late Saturday/early Sunday. Have increased probability of precipitation
across much of the region Saturday evening to account for the faster
timing of the European model (ecmwf). Not expecting to see a lot of Cascade snow with
this front as snow levels quickly rise above 7000 feet early Sunday. We
could see a brief break from the rain Monday as a transient upper
level ridge moves across the region...but will maintain chance probability of precipitation
due to some lingering instability. A weak shortwave could bring some
light showers Tuesday. Another front arrives late Tuesday and should
bring more rain and Cascade snow to the region...with snow levels
lowering to around 3500 feet Wednesday afternoon. Temperatures look to remain
slightly above normal through the forecast...but will trend cooler
after Monday. /64
Aviation...VFR across the board at this hour.With cloud cover likely
inhibiting any potential for widespread fog development. 00z gfs20
time heights are proving to be the best ceiling guidance of the available
options during the dry weather over the last couple days. Ceilings may
lower closer to 050 early this morning but appear to get stuck there.
Models have continued to weaken the incoming front and lamp guidance
continues to trend away from IFR visibility impacts at the coastal taf
sites of kast and konp and are keeping conds as MVFR ceiling/visibility
impacts. Inland taf terminals do not reach MVFR for very long, if at
all during the next 24 hours.
Kpdx and approaches...VFR conditions are the most likely scenario
through the next 24 hours. Ceilings lowering to MVFR of 025-030 under
rain bands today are possible but only give about a 10-20 percent chance.
Broad offshore flow will bring easterly outflow winds from The Gorge
Marine...no significantly large changes to the forecast. Enp is
generally on track with the incoming swell as 10 feet combined seas
reached buoy 89 as of the 0200 hour. Still could extend the Small Craft Advisory for
seas out through Sunday afternoon per enp guidance but prefer to keep
it covered for the periods of higher confidence at this time.
Confused seas will prevail through the better part of the evening
before a singular westerly swell will dominate.
Did lower winds for this first warm frontal period as the surface low
will pivot north and well offshore with the associated surface trough
and tightest pressure gradient mainly staying over the offshore
waters. It will still cover a decent portion of the outer waters. Its
somewhat questionable whether the inner waters will get many gusts
above 21 knots today but dont feel confident enough to pull down the
Next event on the horizon appears to be a potential gale event
Saturday night. Models have come into better agreement though still
differ in the details. Decided to take a 50/50 blend of the GFS and
European model (ecmwf) winds fields. This approach yielded peak gusts 35-37 kts
Saturday night. Prefer to see continued consistency given the
wishy-washy and decaying strength nature of the models over the last
couple events. After that...see a couple shorter Small Craft Advisory type events for
next week. /Jbonk
Pz...Small Craft Advisory for winds from 10 am this morning to
4 am PST Friday for waters from Cape Shoalwater Washington to Cascade
Head or from 10 to 60 nm-waters from Cascade Head to
Florence or from 10 to 60 nm.
Small Craft Advisory for hazardous seas until 4 am PST
Saturday for coastal waters from Cape Shoalwater Washington to
Florence or out 60 nm.
Small Craft Advisory for winds from 4 PM this afternoon to
4 am PST Friday for coastal waters from Cape Shoalwater Washington
to Cascade Head or out 10 nm-coastal waters from Cascade Head
to Florence or out 10 nm.
Small Craft Advisory for rough Columbia River bar until
9 am PST this morning.
Small Craft Advisory for rough Columbia River bar from 4 PM
this afternoon to 11 PM PST this evening.
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.