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Area forecast discussion 
National Weather Service Portland Oregon
313 am PDT Sat Oct 22 2016

Synopsis...showers are coming to an end this morning as yesterday's
upper disturbance races eastward into The Rockies. Meanwhile, weak
high pressure is allowing areas of fog to form in the valleys, which
should burn off by early afternoon. Rapidly developing low pressure
about 300 miles off the Oregon coast will curl north toward Vancouver
Island, pushing a cold front onshore tonight. Rain becomes likely
along the coast this evening, slowly pressing inland through the
night before tapering off Sunday. Low pressure digging south from the
Gulf of Alaska is expected to develop into another strong low Sunday
and Monday, pushing another front onshore by Monday morning. While
the low is expected to remain far enough offshore to prevent strong
winds in the pac NW, disturbances rotating around the system will
keep weather unsettled well into next week.


Short through Monday...National Weather Service Doppler radar continues to
show a few stubborn showers north of a Tillamook to Mt Hood line this
morning, though they do seem to be finally dissipating as shortwave
ridging moves into the region. Weak high pressure is allowing for
some clearing, but with the ground so moist it is not taking long for
fog to form in valleys where skies are clearing. With the sun angle
getting lower this time of year, light winds, and high clouds
expected to be on the increase throughout the day, it may take some
time for the fog and low clouds to completely burn off...perhaps
midday or early afternoon. Decided to keep temps a couple degrees
below most guidance in the valleys today to account for potentially
more persistent cloudiness. Most lowlands should see highs near 60
degrees today.

Satellite water vapor imagery is showing a compact, rapidly
developing low near 44n/134w as of 09z this morning. This system is
producing a number of lightning strikes, indicating the rapid
intensification. Models seem to be struggling to keep up with the
strength of this system, but given the sharp left turn this system is
expected to take, the impacts on the forecast may be minimal - at
least for our land zones. Collaboration with wpc/opc helped determine
that the European model (ecmwf) was the better of the 00z runs in initializing this
system, showing 1006 mb by 06z while others were shallower. The bulk
of the energy with this system will shift north toward the British Columbia coast
this afternoon and evening, but it will push a weakening frontal
system into western Washington/or tonight into Sunday. The 00z ec does show a
little coastal wind tonight...probably gusts 30-40 mph beaches and
headlands. Otherwise the main impact will be some areas of light to
moderate rain spreading inland overnight into Sunday morning, then
dissipating as the front loses its upper level support later Sunday.

Another upper low is presently digging south across the Gulf of
Alaska. This system is also expected to rapidly intensify in the
general vicinity of 45n/135w sun/Sun night. Models are very bullish
in the depth of this low, with many showing central pressure around
965-970 mb by Monday morning. However, the system is expected to
remain far enough offshore to mitigate wind potential for most of the
forecast area. The low will push an occluding frontal system across
the Oregon coast Monday morning. While the deepest moisture is
expected to be aimed toward the or/California border, occasional rain is
still expected across much of our County Warning Area Monday. The cloud cover and
rain should keep temps in the 50s for the lower elevations Monday.
However snow levels should generally remain above pass level through
Monday. Weagle

Long term...(monday night through friday)...much uncertainty in the
extended, as the models diverge significantly later next week. A
broad low pressure system remains off the coast of Washington and
Oregon through the first half of next week. The front associated
with the occlusion of the low moves through on Monday bringing rain
across the area. Tuesday is when the models start to diverge
significantly. The GFS brings a shortwave up the coast bringing
another round of moderate to heavier rainfall on Tuesday night into
early Wednesday. The European model (ecmwf) is slower bringing this system up the
coast, keeping US mostly dry on Tuesday, except some light rain
along the coast. This model brings the midweek system through on
Wednesday into Thursday. Beyond midweek, there appears to be either
a cutoff system that sets up a Rex-block pattern through the end of
the week, or a broad upper-level trough that keeps US rainy into
next weekend. If the Rex block sets up, we could be dry into next
weekend. So essentially, flip a Coin for whether it will be wet or
dry going into next weekend. Snow levels next week are expected to
stay up above 6000 feet, so snow should not be an issue if your
traveling across the passes this week. -McCoy


Aviation...there is a mix of flight conditions across SW
Washington and northwest Oregon this morning. A front pushed through the
region last evening, leaving low level moisture and some residual
clouds around 4-6 kft. In areas where the clouds have scattered
out, IFR or lower fog and stratus has quickly formed. Expect
conditions will eventually settle into mainly IFR stratus over
the northern interior, with LIFR fog over the central and southern
Willamette Valley. Some light offshore flow may keep the coastal
taf sites mainly VFR, but think that some patchy fog will briefly
form at times through the early morning hours. Cigs should lift
and conditions gradually improve to MVFR by late morning, then
VFR in the early afternoon. VFR continues through this evening

Kpdx and approaches...expect IFR stratus through mid-morning, with
improvement to MVFR in the late morning. VFR returns by early
afternoon and continues through this evening. Pyle


Marine...a longer period westerly swell has pushed seas into the
low to mid teens this morning. Think that the seas are peaking
now and will lower a bit later this morning. However, they are
expected to remain around 10 to 12 ft into this evening. A
rapidly developing low pres system apparent on satellite near
43n/135w will lift north toward Vancouver Island tonight. Although
our coastal waters looks to be spared from the strongest winds, S
to southeast winds will pick up quickly later this afternoon and evening.
Expect 20 to 25 kt winds with gusts to 30 kt into early sun am.
There is potential for a few low-end gale force gusts over the
northern waters, but will stay with a Small Craft Advisory for
now. If the 12z model runs come in a bit stronger, a Gale Warning
may need to be considered. The winds will bring increasing
southerly wind waves, which will keep seas above 10 ft through
early sun.

After a lull for much of sun, another potentially much stronger
system is on tap for Sun night into Mon. There are significant
differences in model strength and track at this time. But felt
confident enough in the overall pattern to issue a gale watch
from sun evening through Mon morning. The current fcst contains
S-southeast winds 30 to 35 kt with gusts to 40 kt. It appears that there
is potential for winds to be even higher. This system will likely
push seas at least into the mid teens, possibly pushing 20 ft.

Low pres remains over the NE pac through at least the first half
of next week. Additional strong frontal systems look likely every
24 hrs or so through Wed. There are signs that the weather could
quiet down somewhat for the second half of the week. Pyle


Pqr watches/warnings/advisories...
Pz...gale watch from Sunday evening through Monday morning for
coastal waters from Cape Shoalwater Washington to Florence or out
60 nm.

Small Craft Advisory for winds from 3 PM this afternoon to 5 am
PDT Sunday for waters from Cape Shoalwater Washington to Florence
or from 10 to 60 nm.

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

Small Craft Advisory for winds from 8 PM this evening to 5 am
PDT Sunday for coastal waters from Cape Shoalwater Washington to
Florence or out 10 nm.

Small Craft Advisory for rough Columbia River bar until 5 am
PDT Sunday.



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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.

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