Scientific Forecaster Discussion
fxus66 kpqr 301035
Area forecast discussion
National Weather Service Portland or
335 am PDT Thu Mar 30 2017
Synopsis...showers will decrease today as an upper level
trough of low pressure moves east of the region. Friday will be dry
across the region as high pressure crosses overhead. Another weak
system crosses Saturday with rain returning for most areas. Many
areas may be largely dry Sunday through Tuesday as another upper
ridge tries to build over the pacnw.
Short term...today through Saturday night...showers are picking up
again after a brief lull earlier. The primary cold front has shifted
southeast of the County Warning Area but the upper trough axis is making its
approach and is bringing additional lift and instability to enhance
the north-northwest aligned orographic flow. Showers do gradually
decrease behind the trough axis today, but will be slower to do so
than is typical. A fairly high amplitude upper ridge is closely
following today's exiting trough and will be bringing northerly flow
aloft, however, the right entrance region of the accelerating upper
jet will induce extra lift and keep prolonged showers continuing
mainly over the Cascades well into the evening and early overnight.
Away from the mountains, skies should clear enough to bring some
patchy fog across most of The Lowlands and Coast Range valleys.
Friday will be a rather pleasant Spring day once the fog clears.
The ridge builds Friday night but gets pushed over by deepening low
pressure over the Gulf of Alaska on Saturday. Most of the rain will
be pushed north of our cwa, but there will be enough energy to bring
rain threat. Best chances will be north and west of Salem and
amounts will stay relatively light given the current course of the
last several months.
Temperatures and snow levels will stay somewhat close to seasonal
normals with light accumulations above 3500 feet through tonight,
however snow levels will rise well above the passes Saturday. /Jbonk
Long term...Sunday through Thursday...models are in fairly
good agreement through about Monday with a weak upper trough moving
through the area for a continued low chance of showers although it
might be fairer to say most areas will likely be on the drier side
versus wetter. 00z models are now keeping Tuesday under a passing
dry upper ridge but have left pops intact for the time being until
better run to run consistency develops. They also now have a warm
front clipping the region on Wednesday but are showing little rain
interest and keeping the threat mainly north. The GFS and the European model (ecmwf)
are in good large scale agreement having the Golf low deepen
offshore Wednesday night and Thursday. The details still need some
strong ironing though as the GFS brings a cold front across the
region early Thursday while the ec stalls the front just offshore
while an unseasonably aggressive surface and developing compact upper
develops and swings north just west of 130w. Will certainly want to
keep an eye on the ec solution as a 968mb surface low is highly
unusual this late in the season. Fortunately, the current forecast
track keeps it well offshore with only a glancing blow of winds at
the coast Thursday night. /Jbonk
Aviation...scattered showers this morning will continue to
bring a mix of VFR with MVFR conditions through about 16z. Expect
primarily VFR conditions after 16z this morning as showers decrease,
although there is still a small chance for MVFR cigs through 18z.
VFR conditions expected to remain dominant through 09z tonight, then
there is a chance for MVFR or IFR conditions to develop in the
valleys and at the coast with low stratus or fog.
Kpdx and approaches...primarily VFR conditions today and tonight.
There is a chance for MVFR conditions with showers through 16z this
morning. After 09z tonight chances for MVFR or IFR conditions return
with the potential for the development of fog or low clouds.
Marine...northwest winds around 10 to 15 kt this morning will continue to
weaken today and tonight as a surface ridge of high pres builds over
the waters. A weak front will move east across the waters Sat
morning, but winds are likely to remain under 20 kt with this
system. The next chance for Small Craft Advisory winds comes with
northerly winds over the Oregon waters Sat night and sun.
A west-northwest swell around 10 ft 14 seconds early this morning will subside
a couple of feet today. Seas are expected to remain under 10 ft
until Sat night and sun when a westerly swell arrives and brings
seas up into the 12 to 14 ft range.
Pz...Small Craft Advisory for hazardous seas until 11 am PDT this
morning for coastal waters from Cape Shoalwater Washington to
Florence or out 60 nm.
Small Craft Advisory for rough Columbia River bar until 9 am
PDT this morning.
Small Craft Advisory for rough Columbia River bar from 4 PM
this afternoon to 8 PM PDT this evening.
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