Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
905 am PDT Thursday Oct 2 2014
Synopsis...an upper level ridge with its axis along 130w this
morning will move onshore tonight and remain over the Pacific
northwest Friday...slightly flattening over the weekend but mostly
keeping a front to our north at Bay except perhaps along the far
north coast. The upper ridge will flatten more next week but only
weak energy is expected to move through that may or may not be enough
for some precipitation over the area. All in all...no major storms
are anticipated through the middle part of next week...with rather
pleasant Fall weather most of the time.
Short term...today through Saturday...much less fog and low clouds
this morning across the area...with the main spots the Nehalem River
Valley in the north Oregon Coast Range...along Interstate 5 from
Castle Rock and Kelso south to the Portland Airport...a couple of the
higher Cascade valleys...and south near Eugene. These will burn off
later this morning with plenty of sunshine across the area today.
Expect temperatures inland into the lower 70s.
An upper ridge had its axis out near 130w this morning and will move
onshore tonight...and be over southwest Washington and northwest
Oregon Friday. There is a strong upstream system moving north into
the Gulf of Alaska on the west side of the ridge that has some former
west Pacific typhoon moisture in it. The warm front with this system
will feed some high clouds into the north part of our forecast area
today and into the evening...but it should not be enough to Mar the
pleasant day today. In addition...we will see a bit of northerly flow
across our area with light offshore gradients through The Gorge that
will help this be a nice day today.
The models continue to forecast a weak offshore pattern developing
tonight into Friday...with surface pressure gradients on the nam12
reaching about 5 or 6 mb through The Gorge after midnight tonight and
into Friday. This suggests gusts up in the 30s at places like Corbett
in the west end of The Gorge...a bit higher at Crown Point. Winds
elsewhere will be lighter. Fog late tonight and Friday morning should
again be patchy...mainly in the South Valley...up around Kelso...and
possibly some of the higher sheltered river valleys. The gradient
relaxes significantly by late Friday so expect the winds to do so as
well since the dynamic and thermal forcing is not that strong.
Continue to look for cool nighttime and early morning temperatures...with
some lower 30s in higher sheltered Cascade or Coast Range valleys...
and middle to upper 30s in wind sheltered lower elevations
The upper ridge will remain over our forecast area this weekend...
weakening a bit as the remains of the moist front currently in the
Gulf of Alaska tries to sag into the northern extremes of our
forecast area. We might see some patchy light precipitation in our
far north coastal forecast zones...and some clouds trying to spread
into the north half of our forecast area later Saturday into Sunday
morning...but that appears about it. Tolleson
Long term...no changes. Previous discussion follows...
models continue to advertise upper level ridging over the region
early next week will give way to more zonal flow. This may allow a
weak shortwave trough or two to impact the region at some point
towards the middle of next week. As a result...slight chance probability of precipitation
were kept in the forecast in the extended. Nonetheless...the probability of precipitation are
still a touch lower than climatology and temperatures were kept near to
slightly above normal. /Neuman
Aviation...high pressure and clear skies allowed some very patchy fog
and low stratus to form over parts of the region early this morning.
The main locations impacted include the southern Willamette Valley
and the lower Columbia Basin from about Astoria to just west of the
Portland/Vancouver metropolitan area. These locations may see brief MVFR/IFR
ceilings or visibilities through 16z or 17z. Then expect widespread VFR
conditions with sunny skies over the entire region through this
evening. Developing offshore flow will likely allow VFR to persist
overnight and Friday morning...although some patchy fog over the central
and southern Willamette Valley is possible from about 12z to 16z.
Kpdx and approaches...there is a slight chance of a brief IFR ceiling
through about 17z. Otherwise expect VFR conditions through the next
24 hours. Gusty east winds may affect areas out toward The Gorge
tonight into Friday morning. Pyle
Marine...overall remaining rather quiet through the weekend. High
pressure remaining offshore will keep winds roughly out of the north. A
trough of low pressure along the S Oregon coast will cause winds to pick
up each afternoon and evening to around 20kt before weakening again
in the mornings. Seas around 5 feet today and Friday expected to increase
to around 7 feet for the weekend as swell arrives from the west.
Strengthening north winds Monday may see winds in the southern waters
gusting to 25 knots by the end of the day.
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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.