Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland Oregon
246 am PDT Thu Oct 27 2016
Synopsis...a frontal boundary continued to extend from near the
South Washington Cascades to the south Oregon coast early this
morning. The front will slowly shift east this morning then
accelerate eastward this afternoon with rain decreasing. Another
disturbance moving through today will help push the frontal zone out
of the area but spread some showers over the forecast area, and
possibly a thunderstorm mainly across the north half of the area this
afternoon. One more disturbance will swing northeast and brush the
northwest part of the forecast area tonight. This will be followed by
a lull in precipitation Friday. The next low is expected to set up
off the coast Friday night, with another round of unsettled weather
expected through the weekend and possibly into early next week.
Short term...(today through saturday)...National Weather Service
Doppler radar continued to show plenty of echoes and steady rain from
the central Oregon Coast Range and the south Willamette Valley
northward toward the South Washington Cascades early this morning.
This band is starting to make some slow eastward movement. The models
show an upper trough off the coast will swing northeastward through
the forecast area today, which should push the front eastward with
decreasing rain. However, this trough will spread some showers and
instability through the area by afternoon, with a small chance of
thunder especially north, and a little slower arrival than the models
The models then show the southern end of the band out near 140w will
swing northeast and brush especially the northwest half of the
forecast area with some more showers tonight. This system lifts north
of the area by Friday morning.
Friday will see a lull in precipitation, with dry conditions possible
in much of southwest Washington and northwest Oregon. There might be
a few residual showers near the coast and over the Coast Range. There
is a possibility of some fog and low clouds Friday morning as well.
The next low sets up off the coast Friday night and remains anchored
off the coast Saturday. The models show a good shot of precipitation
spreading northward overnight Friday night and Saturday morning in
the resulting southerly flow, with some moisture likely lingering
into the afternoon Saturday as well. Tolleson
Long term...no changes. Previous discussion follows...
(saturday night through wednesday)...12z deterministic models were
generally in good agreement through Sunday, bringing the next large
upper low onshore as an open wave for more cool and unsettled weather
over the weekend. Shortwave ridging may result in a brief lull in
shower activity Sun night or Mon, but models diverge quickly at that
point and beyond. One thing models do agree on for early next week is
that at least some sort of troughing will persist over the NE
Pacific, but details vary widely between the generally drier 12z
European model (ecmwf) and the wetter GFS which keeps the flow pattern more
progressive. Will hold off on committing to either solution right
now, keeping pops and temps fairly close to climo Mon-Wed but hedging
slightly toward the cool/wet side. Weagle
Aviation...a cold front still lies over the inland areas, but should
weaken further as it slowly shifts eastward over the Cascades this
am. Generally, VFR has dominated and see no reason to expect
otherwise today. Will continue to see pockets of MVFR or possibly
brief IFR against the Cascades, as well as the coastal mountains this
am. Light rain inland this am, but will decrease and transition to
showers by the afternoon. Air mass somewhat unstable, so can not rule
out a few isolated thunderstorms, mainly west of a Mt St helens to
Portland to Newport line. Showers will decrease quickly this evening.
Kpdx and approaches...not much change, with VFR and light rain this
am. Rain will taper off, and becoming showery in nature after 18z.
With unstable air mass, could see a few heavier showers and possibly
a thunderstorm in Ops area after 20z. But best threat for tstorms
will be over and to west of coast mtns. Rockey.
Marine...not a lot of change in the overall pattern. Broad area of
low pressure remains over the Gulf of Alaska. This will continue to
send fronts barreling towards the pacnw through the weekend.Jet is
such that the main lows that spin up well offshore will continue to
remain well offshore and move to Vancouver Island.
Currently, continue to see southerly winds 20 to 25 kt on the waters,
with a south to southwest swell of 10 to 12 ft. Seas will subside
today. There will be somewhat slacker winds for awhile this am, but
winds will pick up again later today as another weak cold front moves
across the waters.
Conditions then look quieter over later Fri into the weekend with
winds generally 15 kt or less. Seas 6 to 8 ft Fri, but another fetch
of westerly swell will arrive Fri night and Sat, with overall seas
running 10 to 12 ft. Rockey.
Pz...Small Craft Advisory for winds through tonight on all coastal
Small Craft Advisory for hazardous seas today on all coastal
Small Craft Advisory for rough Columbia River bar until 5 am
today, and again 1 to 5 PM later today.
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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.