Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
302 am PDT sun Mar 16 2014
Synopsis...a quasi-stationary front will remain near the olympic
peninsula through this morning with rain or drizzle across far
northwest Oregon and southwest Washington. The leading edge of the
front will slowly sag south to near the Portland area this afternoon.
More widespread and heavier rain will sweep through southwest
Washington and northwest Oregon tonight. The front will move east of
the Cascades between midnight tonight and day break Monday. The
biggest story is the dramatically lowering snow levels tonight and
Monday that will lower into the higher Cascade foothills. Heavy snow
is possible in the Cascades as well tonight. Look for cooler
temperatures this week as well. Another disturbance will drop in
from the northwest Monday night and Tuesday...with another Tuesday
night and especially Wednesday...continuing the unsettled and cool
pattern through at least midweek.
Short term...as expected...the wet frontal boundary continues to be
hung up in western Washington...clipping our far northern forecast
zones north of the Columbia River...except to around Astoria or a bit
south of there near the coast. Snow levels are currently quite high
with a mild air mass south of the front.
The front will begin moving south this afternoon...with the leading
edge of the precipitation reaching a Lincoln City to Portland line
later in the day. The front will the sweep across southwest
Washington and northwest Oregon tonight...moving east of the Cascades
between midnight and 5 or 6 am Monday. Snow levels will fall
dramatically as the front moves through...to as low as about 2000
feet late tonight and Monday...into the higher elevations of the
Cascade foothills and the Coast Range.
As the front sweeps through tonight...the precipitation will be
locally heavy...with locally heavy snow in the Cascades. Will issue a
Snow Advisory with this forecast package issuance. Once the front
moves through late tonight...the showers behind the front are not
very impressive and we will only get relatively minor accumulations
The models continue to focus on a weak overrunning wave moving in
from the northwest Monday night and Tuesday. This feature is not very
strong...but should give US some more areas of light valley rain and
light mountain snow Monday night into Tuesday decreasing later
Long term...no changes. Previous discussion follows...
Tuesday night through Saturday...the 12z runs of the extended forecast
models have continued the trend of the past few model cycles in
bringing a cold front through the region around midweek. The
ensembles are now showing good agreement that an upper level trough
will move into the Pacific northwest late Wednesday into Thursday. Decided to bump up probability of precipitation
considerably during this time period...but quantitative precipitation forecast totals are modest at
this point. Beyond this system...do not currently see any other well
organized precipitation for the region into next weekend. Expect
primarily cyclonic flow aloft in a fairly progressive pattern through
next weekend. A weak system moving onshore over North Washington or British
Columbia may bring showers or drizzle at times Thursday or Friday...
especially for the northernmost parts of the forecast area. Overall...
expect temperatures on the cooler side of normal through the extended period
with quite a bit of cloud cover in onshore flow. Pyle
Aviation...expect conditions to deteriorate into IFR along the coast
and MVFR inland as a frontal system slowly sags southward today.
Frontal passage should occur this morning at kast...and as late as
middle evening at keug. Instability behind the front should lead to most
locations trending VFR tonight.
Kpdx and approaches...a mix of VFR and MVFR conditions will likely
occur this morning...but VFR conditions should be the dominant flight
condition. Frontal passage still appears on track for 00z to 02z
Monday. A more consistent period of MVFR conditions will likely
accompany frontal passage as steadier precipitation moves overhead.
However...increasing low level instability behind the front should
lead to conditions trending VFR Sunday night. /Neuman
Marine...south winds ahead of a front have been underachieving
across the waters this morning. As a result...I put a mention of
occasional gusts to 25 knots in the coastal waters forecast for this morning...but opted to
have the Small Craft Advisory for winds focus on the gusty
northwesterly winds that will arrive Sunday evening and Sunday night.
Gusts of 30 knots appear likely during that time...especially across the
Otherwise...seas in the low teens early this morning...will rise
sharply late this morning. Kept with the idea that seas will likely
peak in the 16 to 18 feet range this afternoon...before slowly falling
Sunday night into Monday. Seas will likely drop below 10 feet sometime
later Monday...possibly as late as early Tuesday. However...expect
this respite to be short lived as another 10 to 12 feet westerly swell
arrives Wednesday. A burst of 25 to 30 knots winds will also likely
accompany this swell train as a low pressure moves southeastward
through British Columbia. A more Summer like weather pattern appears
likely late in the week so the central Oregon waters may see some
gusty evening winds from time to time. /Neuman
or...Winter Weather Advisory from 6 PM this evening to 5 am PDT
Monday for northern Oregon Cascades.
Winter Weather Advisory from 7 PM this evening to 5 am PDT
Monday for Cascades in Lane County.
Washington...Winter Weather Advisory from 4 PM this afternoon to 1 am PDT
Monday for South Washington Cascades.
Pz...Small Craft Advisory for winds from 3 PM this afternoon to 9 am
PDT Monday for coastal waters from Cape Shoalwater Washington to
Florence 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 rough Columbia River bar until 5 PM PDT
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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.