Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
754 PM PDT Wed Jul 27 2016
Synopsis...weak upper ridging is bringing the warmest temperatures
we've seen this July to inland locations of southwest Washington and
northwest Oregon through Friday. Inland temps are getting up to
around 10 degrees above normal, capped by light westerly flow aloft
and continued light onshore flow. The models continue to indicate
that an upper trough will settle southward along the coast this
weekend and early next week for cooler temps, more night and morning
low clouds, and perhaps a little drizzle or showers mainly near the
Short term...(today through saturday)...no changes. Previous
discussion follows...heights have begun to build across the area as a
Flat Ridge strengthens over the Pacific northwest for the second half of the
work-week. This will lead to a persistent pattern of morning coastal
clouds burning off the coast by mid day, warm temperatures, and
northerly winds. Subsidence aloft will compress the marine layer
enough to keep inland stratus intrusion at Bay Thursday and Friday
morning. If anything does form in the Willamette Valley, expect it to
be scattered in nature.
High temperatures in the low 90s inland are still looking like a safe
bet, especially if skies are mostly clear tomorrow morning as
Heights will begin to fall by Friday night as an upper low drops
south out of the Gulf of Alaska and towards British Columbia. This
will mark the end of the warm spell with temperatures returning to
near normal into the long term period. /Bentley
Long term...(saturday night through wednesday)...no changes.
Previous discussion follows...near normal temperatures will continue
through the long term period as model consensus has converged on a
general troughiness pattern across the Pacific northwest. These passing
troughs will act to increase cloudiness in the area, but will produce
little precipitation due to the better forcing further north and
relatively high heights. /Bentley
Aviation...marine clouds with mainly IFR cigs remained along
the coast this evening, extending a short ways inland. VFR
conditions elsewhere this evening. With a weakened onshore flow
tonight, expect marine clouds to push inland overnight in the north,
but not as vigorously as last night. This is likely to leave coastal
taf sites as IFR overnight through about 19z Thu. There is about a
30 percent chance for a return to VFR conditions later tonight or
Thu morning as marine clouds are not likely to push far inland
overnight. Inland areas likely to remain VFR...with just a chance
for kttd and kpdx to see a brief period of MVFR or high end IFR cigs
between 13z and 18z.
Kpdx and approaches...generally VFR conditions tonight and Thu.
About a 30 percent chance of seeing MVFR or high end IFR cigs
between 13z and 18z Thu morning.
Marine...surface high pres will persist over the NE pac through
the end of the week, with a thermal induced trough along the north California
and S or coast. Wind gusts close to 30 kt possible through the
evening over far southern pzz255 and pzz275. Little change in the
pattern Thu through Fri. Small craft Wind Advisory continues until
12z Fri for all zones except pzz250. Wind will ease in the north
inner waters tonight, but return to Small Craft Advisory thresholds
Thu afternoon. Wind speeds expected to subside somewhat over the
weekend as the NE pac surface high weakens.
Steep waves through Fri will remain dominated by the locally
generated wind waves and fresh swell.
Question remains whether to include pzz250 and pzz270 in the Small
Craft Advisory for hazardous seas. Southern waters and northern
outer waters are likely to remain with wave heights near or a little
in excess of wave periods, or effectively, square seas. With buoy
46089 running close to this criteria, and expected to remain with
small craft winds, will add pzz270 to the Small Craft Advisory for
winds through Thu night. As winds subside some over the weekend,
locally driven wind waves will also subside, but a fresh swell
from the NNW will keep seas steep.
Pz...Small Craft Advisory for winds until 5 am PDT Friday for
coastal waters from Cascade Head to Florence or out 10 nm-
waters from Cape Shoalwater Washington to Florence or from 10 to
Small Craft Advisory for hazardous seas until 5 am PDT Friday
for coastal waters from Cascade Head to Florence or out 10
nm-waters from Cape Shoalwater Washington to Florence or from 10
to 60 nm.
Small Craft Advisory for winds until midnight PDT tonight for
coastal waters from Cape Shoalwater Washington to Cascade Head or
out 10 nm.
Small Craft Advisory for winds from 1 PM to 11 PM PDT Thursday
for coastal waters from Cape Shoalwater Washington to Cascade Head
or out 10 nm.
Interact with US via social media:
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.