Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
253 am PDT Sat Mar 15 2014
Synopsis...the edge of a warm front associated with the next system
will brush the coastal waters and the far north sections of our
forecast area with a little light rain or sprinkles today. The
associated very wet cold front will remain north of our area in
western Washington today...slowly sagging into our northern forecast
zones tonight and Sunday...then sweeping through southwest Washington
and northwest Oregon Sunday night and early Monday with a good shot
of rain. This front will also dramatically lower snow levels and
produce some locally heavy snow in the mountains. Cool showery
northwesterly onshore flow will be over the forecast area Monday with
more snow in the mountains. The middle part of next week is more
uncertain and may not stay dry if recent model runs are to be
believed. More rain expected later next week.
Short term...infrared satellite imagery and National Weather Service
radar show clouds and some light echoes across parts of our coastal
waters and near the north coast forecast zones early this
morning...somewhat similar to the models. The models show the edge of
a warm front associated with the next system brushing our waters and
far north zones today...trying to lift north in the afternoon.
Amounts will be quite light. Otherwise we do have a chance of some
fog or low clouds developing down the Willamette Valley and locally
along the coast this morning.
The main cold front and moisture feed is oriented to our north into
western Washington...and will tend to stay north today. The cold
front very slowly sags south into our northern forecast zones tonight
and Sunday with slowly increasing chances of rain...possibly getting
into the Portland area either late tonight or on Sunday.
The main cold front then drives southeastward across southwest
Washington and northwest Oregon Sunday night as a vigorous upper
level short wave moves through. This will bring a good shot of rain
Sunday night to our area that could be locally heavy. Precipitable waters are over an
inch feeding this frontal band. In addition...strong cold advection
will drive snow levels to below the passes Sunday night... and as low
as about 2000 feet by early Monday. The snow could be locally heavy
as well...and may require a Snow Advisory. Cool northwest onshore
flow trailing the cold front will keep snow levels down around 2000
feet or possibly even a little lower on Monday. This could give some
accumulations into the higher Cascade foothills and the Coast Range.
The showers and onshore flow should wane by Monday evening. Tolleson
Long term...recent model runs show some uncertainty with dry weather
during the middle week period...with a flatter dirty upper ridge. For
now will wait another model run or two for consistency before making
any changes per coordination with neighboring offices. The remainder
of the previous discussion is unchanged...Monday night through
Friday...upper ridging briefly rebounds Tuesday and Wednesday...
ahead of trough of low pressure that will push a cold front through
the region late Wednesday. Showery conditions look to persist through
Thursday under cyclonic flow aloft as the upper trough moves east. By
late Thursday model agreement degrades somewhat...both depict a short
wave or two moving through fast northwest flow late in the week but
disagree on the details. Overall...expect progressive conditions to
prevail through the extended. Bb
Aviation...high pressure across the region is currently producing
VFR conditions. These improved conditions will give way to a
deterioration of conditions along the coast Saturday...and late
Saturday night for inland locations.
Kpdx and approaches...expect VFR conditions through at least Saturday
evening. MVFR conditions will be possible after 06z Sunday. /Neuman
Marine...relatively lights winds currently across the waters will
turn southerly and increase to 20 to 25 knots this morning. Wind gusts
may approach 30 knots across the northern waters this afternoon and
evening. Expect Post frontal westerly winds to be light Saturday
night into Sunday...before becoming gusty into 25 knots to 30 knots range
Sunday night. High pressure over the northeast Pacific and thermal
low pressure over California will bring a return to more of a
Summer-like wind pattern Monday and Tuesday...with gusty evening
winds across the central Oregon waters.
Seas are currently in the 10 to 11 feet range and will increase a
couple more feet today...before a larger westerly swell arrives
Sunday morning. This larger westerly swell will top out in the 16 to
19 feet range for approximately 6 hours around midday Sunday. Seas
should then subside steadily...before falling below 10 feet late Monday
or early Tuesday. Another swell around 10 feet appears on tap for
Pz...Small Craft Advisory for winds from 6 am this morning to 5 am
PDT Sunday for coastal waters from Cape Shoalwater Washington to
Cascade Head or out 60 nm.
Small Craft Advisory for hazardous seas until 5 PM PDT Monday
for coastal waters from Cape Shoalwater Washington to Florence or out
Small Craft Advisory for winds from 9 am this morning to 11 am
PDT Sunday for coastal waters from Cascade Head or to Florence
or out 60 nm.
Small Craft Advisory for rough Columbia River bar until 5 PM
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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.