Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland
302 am PDT sun Mar 29 2015
Synopsis...mild and mostly dry weather through Monday as flat upper
level ridging remains over the Pacific northwest. A cold front will push across
the region late Monday...ushering in a much cooler and more
seasonable air mass...along with showers and lower snow levels
through the end of the workweek.
Short term...Sunday through Tuesday... a little bit of very light
rain on radar tonight potentially affecting the South Washington and
north Oregon coasts...but not sure much if any rain is actually
reaching the surface. Otherwise dry conditions overnight tonight and
through Sunday into Monday as ridging remains over the area.
Afternoon high temperatures should climb back into the middle to upper 60s over
the interior lowlands this afternoon with a near repeat Monday.
An upper level trough will dive down from the Gulf of Alaska on
Monday...finally driving a stalled frontal boundary off Vancouver Island
onshore as a cold front. Expect rain to push onto the coast Monday
evening...then inland overnight although models continue to trend
slightly later with timing of the front. The upper level trough will
move through on Tuesday...ushering in a significantly cooler air mass.
The forecast models are indicating that there will be plenty of
postfrontal showers across the region on Tuesday. Forecast model
soundings show some instability and forcing with the front Monday
night and a bit into Tuesday morning...but it looks like there may be
too much of a cap to really produce any thunder so have left it out
for now. However it may be one of those days with periodic heavy
showers...some containing small hail. The colder air should also drop
snow levels down to Cascade passes where several inches of
accumulating snow may fall. Bowen/pyle
Long term (previous discussion)...Tuesday night through Friday...a
progressive pattern is expected for the extended forecast period. Behind
the upper level trough on Tuesday...forecast confidence is fairly high that
another shortwave will move onshore Wednesday...bringing continued showers
and mountain snow into Thursday morning. There is then a shortwave upper
level ridge that is modeled to move into the region on Thursday. This may
end up providing a brief break from the shower activity later Thursday
into Friday before a deep upper trough moves toward the coast on Friday
into next weekend. Forecast confidence becomes lower toward the end of
the week. Friday could end up being mostly dry...but the forecast models
seem to be trending toward speeding up the arrival of the deep
trough...which would bring more rain onshore Friday. Pyle
Aviation...VFR conditions expected to continue through today and
tonight. High-level clouds should keep any fog from forming at
inland sites. Light off-shore winds are helping keep the coast
clear as well. There are a few light showers being seen on radar
that are approaching kast. Thought is that these will fizzle out
before reaching kast...but a few sprinkles are possible.
Confidence is not high enough to have in taf...though these will
probably bring in a middle-level cloud deck.
Kpdx and approaches...VFR conditions expected through 06z Monday.
Marine...pressure gradient across the northern outer waters is
likely generating low-end small craft winds in this area.
Satellite-derived winds from a pass around 1000 PM is showing
15-20 knots winds clipping the northern outer waters. This gradient
should be relaxing and winds should decrease back below small
craft criteria over the next few hours.
Seas have been holding around 8 feet this morning...but larger swell
generated from the low pressure system over the Gulf of Alaska
will start moving in over the next couple hours. Observations out
at buoy 5 have supported swell coming in all the way to the coast
around 10 feet. Seas should hover around 9 to 10 feet through early
Monday so a Small Craft Advisory will be issued for this period
across the outer and inner waters.
Sunday evening...winds should start to pick up out of the south
ahead of our next frontal system which will move through Monday
evening. A Small Craft Advisory for winds and seas will likely be
needed ahead of this system on Monday. Winds should ramp up to 20
to 25 kts just ahead of the front...gusting to 30 kts...and seas
should build to 10 to 12 feet Monday night and stay up through early
Pz...Small Craft Advisory for winds until 5 am PDT early this morning
for waters from Cape Shoalwater Washington to Cascade Head or from 10 to
Small Craft Advisory for hazardous seas from 5 am early this
morning to 5 PM PDT this afternoon 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 rough Columbia River bar until 3 am PDT
early this morning.
Small Craft Advisory for rough Columbia River bar from 11 am
this morning to 5 PM PDT this afternoon.
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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.