Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Portland or
233 am PDT sun Apr 20 2014

Synopsis...high pressure will bring mainly dry and a little warmer
weather today. The next Pacific cold front will approach the region
Monday and move through Monday night bringing a cooler showery air mass. A
warm front approaching the coast will keep a threat for showers
going Wednesday...then another cool showery trough is expected late in the
week.
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Short term...early this morning it looked like the last of the
showers associated with the departing trough were coming to an end
over the north part of the forecast area. A transient surface high is
expected to move across the Pacific northwest today for dry and warmer
weather. The warm front lifting up to the Washington coast appears to
lack moist isentropic lift this morning so will drop the chance for
showers on the S Washington coast.

Next Pacific system expected to approach Monday. Models continue to
show the trough digging as it approaches the coast...so initially
the front is expected to be slow to reach the coast with much of the
best dynamics headed S. Flow however backs to the south-southwest aloft Monday
bringing middle and upper level moisture up into the region. Will
continue to carry an increasing threat for showers Monday and Monday
night...but hold off on likely or higher probability of precipitation until Monday night when
the front band finally pushes inland and the upper trough axis
finally reaches the coast. As the cool upper trough moves inland
showery conditions will persist into Tuesday. This will also usher in
below normal temperatures Wednesday as 800 mb temperatures go below zero c.

Long term...no changes. Previous discussion follows...Tuesday night
through Saturday... the extended portion of the forecast is looking
increasingly wet with below normal temperatures. We start out fairly
quiet Tuesday night and early Wednesday...with a few showers around on the
backside of an upper level trough that is departing to the east. The
next frontal system is expected to bring steady rain beginning Wednesday or
early Thursday. Confidence in the timing of this system is not high at
this point. The 12z European model (ecmwf) run came in much more progressive than past
runs...bringing rain onshore Wednesday afternoon. The 12z GFS and the
majority of its ensembles hold the rain off until overnight Wednesday into
Thursday. At any rate...precipitable water values with this system are
looking fairly high so we will likely get a pretty good dose of rain
through Thursday night. A broad and cold upper level trough will build
into the NE Pacific for Friday into next weekend...bring more rain chances.
Pyle
&&

Aviation...generally VFR conditions across the region early this
morning. Along the coast...persistent scattered clouds around
2000-3000 feet have occasionally formed a broken deck. Expect periodic
MVFR ceilings/visibilities to continue along the coast through daybreak. Over
the interior...expect the middle and high clouds to gradually
clear...which will likely lead to low stratus or fog
development...especially in south and central Willamette
Valley. Any fog that forms will likely be patchy and dissipate
around 18z giving way to VFR conditions on sun.

Kpdx and approaches...VFR through at least 12z. Some patchy
fog/low stratus possible after 12z...with chance for MVFR through
17z-18z. Any that does develop will dissipate by 18z giving way
to VFR conditions through sun. Cullen

&&

Marine...the large westerly swell train reached the outer waters
around 11 PM last night as expected...bringing rapidly building
seas to the coastal waters. Buoy 46089 peaked 24 feet at 16 seconds
and remains near 22 feet. This swell continues to move across the
waters...as buoy 46029 has reached 20 feet and 46050 has reached 22
feet at this hour. Still expect the peak between now and 6 am this
morning...before seas will gradually subside through the day
today...diminishing to around 15 feet tonight...and to 10 feet Tuesday
morning. The high surf advisory for the S Washington...north
Oregon...and central Oregon coasts continues through 10 am today.
Not a good time to be in or near the surf zone today.

A relatively quiet period in terms of wind over the waters
through the first half of this week. A weak system will approach
the waters this afternoon and could bring a few occasional gusts
to 20-25 knots over the far northern outer waters. Otherwise...the
next significant system arrives late Wednesday or Thursday...likely bringing
small craft winds. Cullen



&&

Pqr watches/warnings/advisories...
or...high surf advisory until 10 am PDT this morning for central
Oregon coast-north Oregon coast.

Washington...high surf advisory until 10 am PDT this morning for South
Washington coast.

Pz...Small Craft Advisory for hazardous seas until 5 am PDT Tuesday
for coastal waters from Cape Shoalwater Washington to Florence or out
60 nm.

Small Craft Advisory for rough Columbia River bar until 3 am
PDT Monday.

&&

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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..