Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus66 kpqr 220916 
afdpqr

Area forecast discussion
National Weather Service Portland or
214 am PDT Thu Jun 22 2017

Synopsis...high pressure aloft over the forecast area will
strengthen through the weekend. A thermally-induced surface trough
and resultant offshore low-level flow will result in hot temperatures
Friday through the weekend. A southwest marine surge occurs along the
central coast Saturday night and Sunday. A deeper marine push occurs
Monday for much cooler temperatures inland. Strong onshore flow
continues Tuesday through mid-week, followed by a gradual warming
trend late in the week.
&&

Short term...Thursday through Saturday...the main story for the
short term will be hot daytime temperatures Fri and Sat. Water vapor
imagery shows a large 596 dm high pres center near 39n 136w, which is
resulting in northwest flow aloft over the pac northwest. Wed Max temps were quite
pleasant, but much warmer conditions are on the way. The high-res arw
and NAM show minimal to no low clouds this morning, with both models
suggesting north-NE boundary layer and 975 mb flow. There may be some
patchy low clouds or fog along the coast, but confidence is fairly
low. The 00z ksle sounding came in with 10c at 850 mb. The GFS, NAM
and European model (ecmwf) all show close to 14c valid 00z Fri. This should translate
to at least 5-7 deg warming inland. NAM continues to show a moderate
north-to-south surface gradient through the Willamette Valley Thu,
which will produce afternoon north wind gusts to at least 20 mph.

A thermally-induced surface trough strengthens along the coast Thu
night and would expect subsidence inversions to become more
pronounced in the Oregon Coast Range and all Cascades and foothills
areas. More substantial warming occurs Fri with 850 mb temps near to
slightly above 20c. Offshore low-level flow develops Fri as well,
which will help to boost temps through downslope compression. Even
the coast should get into the act Fri, with 75 to 80 possible,
especially along the north Oregon and S Washington coast. The
thermally-induced surface trough settles over the coast, Oregon Coast
Range and SW Washington Willapa Hills Fri night and Sat. Models in
general agreement showing 850 mb temps near 22c by 00z sun. Coupled
with continued offshore flow, inland valley temps expected to be in
the mid to upper 90s. There is also the potential for places like
kast and ktmk to get close to 90 deg Sat. The latest NAM run hints at
a south flow reversal along the South Coast late Sat afternoon,
possibly reaching Florence by 00z sun.

Sat Max temps will be tricky. The operational runs of the GFS and
European model (ecmwf) continue to be at the top end of the ensembles. In fact, there
are plenty of ensemble members from both the gefs and ec that suggest
it will be difficult for the Willamette Valley to reach much above
the mid 90s this weekend. As a result, confidence in whether or not
this will be a somewhat routine hot spell with temperatures topping
out near or slightly above 90f or record breaking with temperatures
topping out near 100f is still somewhat uncertain at this point.
Either way, the same general heat related precautions and messages
apply. Weishaar

Long term...Saturday night through Thursday...the NAM shows the
south coastal surge moving up the coastline Sat night, getting close
to ktmk by 12z sun. Some of this marine air will likely seep into the
central Oregon Coast Range valleys. However, light offshore low-level
flow continues elsewhere, with strong subsidence inversions remaining
in place for the Cascades. The operational GFS and European model (ecmwf) show 850 mb
temps sun peaking around 24c. Went a touch lower sun inland compared
to Sat. The surface thermal trough may remain over the interior
valleys and near the Cascades sun so Max temps could end up slightly
warmer than forecast. The European model (ecmwf) hints at some mid-level moisture
spreading north from north. Cal Sun afternoon. Also, the European model (ecmwf) has a
short-wave moving over the top of the 500 mb ridge Sun afternoon,
lowering heights just a bit.

Cooling occurs Mon as a short-wave reaches SW Oregon and another
disturbance moves into southern b.C.. the European model (ecmwf) would suggest the
potential for elevated convection for the Cascades and possibly
foothills Mon afternoon, followed by a much deeper marine surge Mon
night. The deep marine layer holds Tue and Wed with daytime temps a
little below normal. High pressure strengthens late in the week for a
return to seasonal conditions. Weishaar

&&



Aviation...mostly clear skies and VFR conditions today and
tonight. Marine stratus with low MVFR cigs may form along north
coast ear;y this morning, but light offshore winds will likely
keep most of this stratus away from the airports. Think inland
areas are too dry to support much if any stratus this morning.

North winds will increase in the afternoon in most locations,
but be especially gusty (25 to 30 kt) along the coast south of
ktmk.

Kpdx and approaches...VFR with mostly clear skies today and
tonight. North winds will increase this afternoon with 20 to 25
kt gusts possible through the early evening. ~Tj

&&

Marine...there will be persistent north winds over the waters
through Saturday due to high pressure over the NE Pacific and
thermal low pressure over northwest California and S Oregon. The winds
will be strongest south of Cascade Head, with frequent gusts of
25 to 30 kt. Winds within 10 nm of the coast will weaken during
the nights, and become offshore through the early mornings. The
winds will build steep and choppy seas that will reach heights of
8 to 10 feet south of Cascade Head at times.

Weak low pressure develops across the waters Saturday night and
holds through Monday. This will result in a southerly wind
reversal for the waters mainly within 10 nm. ~Tj



&&

Pqr watches/warnings/advisories...
or...none.
Washington...none.
Pz...Small Craft Advisory for winds until 5 am PDT Saturday for
waters from Cape Shoalwater Washington to Florence or from 10 to
60 nm.

Small Craft Advisory for winds until 11 PM PDT Friday for
coastal waters from Cape Shoalwater Washington to Florence or out
10 nm.

Small Craft Advisory for hazardous seas until midnight PDT
tonight for coastal waters from Cascade Head or to
Florence or out 60 nm.

Small Craft Advisory for rough Columbia River bar until 7 am
PDT this morning.

&&

$$

Interact with US via social media:
www.Facebook.Com/nwsportland

National Weather Service Glossary of Abbreviations