Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 270311
Area Forecast Discussion
National Weather Service Portland OR
810 PM PDT Tue Jul 26 2016
.SYNOPSIS...A weak upper trough near the coast with a weak westerly
flow aloft over the Pacific Northwest will continue tonight into
early Wednesday with morning low clouds giving way to afternoon
sunshine and seasonable afternoon temperatures. An upper level ridge
will build for the second half of the week and bring inland highs
well into the 90s Thursday and Friday before a weak trough arrives to
moderate temperatures and increase clouds over the weekend.
.SHORT TERM...(Today through Thursday)...Stratus is already moving
back onto the Coast, while the rest of the area is under clear skies.
With a very weak shortwave moving through tonight, we`ll see stratus
push back inland Wednesday morning, in a similar manner to this
morning. Could see some patchy drizzle for the far North Oregon and
South Washington Coast where the shortwave may generate enough lift
to support it. Otherwise skies should clear out again Wednesday
afternoon with temperatures slightly warmer than today. Will see less
and less morning clouds inland Thursday and Friday leading to a
warming trend inland toward the end of the work week.
The main discrepancy in the forecast is how warm we will get inland
Thursday and Friday. While the ECMWF shows 850 temps getting up
around 20C-22C, the GFS is more modest with 850 temps only around
16C-18C. 850 temps from the ECMWF would support highs in the upper
90s while the GFS would only support temps getting up into the lower
90s. Right now leaning towards the GFS with the lower 90s due to the
flatter nature of the ridge, and also due to the flow, though weak,
generally continuing to be onshore. Really don`t have the offshore
component to the wind to help dry and warm the airmass. Due to
onshore flow continuing on Thursday and Friday, the Coast will stay
much cooler than inland, with highs generally in the upper 60s to
lower 70s. -McCoy
.LONG TERM...(Friday night through Tuesday)...Heights begin to fall
Friday night as a deeper upper level low moves from the Gulf of
Alaska into southern British Columbia. Still some disagreement among
the forecast models in the track and depth of the upper trough, but
generally expect a cooler and cloudier weekend and start to next
week. Introduced a slight chance of showers for the northwestern
portion of the forecast area early Sunday as this upper trough and
associated surface front slides across, but moisture looks quite
minimal so will hold off on anything higher than that for now.
Onshore flow aloft will prevail through the first portion of next
week with another reinforcing impulse crossing the region around
Tuesday, keeping temperatures a few degrees below seasonal norms.
.AVIATION...Marine stratus was beginning to make a push back onto
the coast this evening. KAST was already in solid with MVFR cigs
by early evening, while further south stratus was just forming.
Expect the north coast to remain mainly MVFR overnight and into wed
morning. Northerly flow along the central OR coast will slow
development of clouds, with areas of low end MVFR to IFR conditions
developing through 12Z. Stratus expected to push inland late
tonight, mainly up the Lower Columbia into the North Willamette
Valley, with MVFR cigs vicinity of KPDX between 12Z and 19Z. Stratus
is likely to burn back to the coast quicker Wed than Tue, with KAST
likely the last TAF site to clear and return to VFR conditions after
KPDX AND APPROACHES...VFR through tonight. There is a high
probability that MVFR conditions will return with marine stratus
after 12Z, before returning to VFR conditions around midday at 19Z.
.MARINE...Small craft advisory level winds gusting to 25 kt across
the southern waters early this evening in response to the trough of
low pres along the south Oregon coast. Surface pres gradients
expected to remain strong overnight and into Wed, so will hang onto
the advisory for winds in the southern waters. In the north, winds
generally have been under 20 kt. Models suggest a little
strengthening of pres gradients across the north Wed afternoon in an
otherwise similar weather pattern, so will keep small craft advisory
posted for the north beginning midday Wed. Gusts in the extreme
southern PZZ255 and PZZ275 could see near-gale force gusts late Wed.
The overall pattern to remain virtually unchanged Thu and Fri. The
next upper trough is expected to swing across the area this weekend,
which will deepen the marine layer and reduce wind speeds.
As northerly winds pick up and continue for the next few days, seas
will be dominated by short period locally generated waves. This
results in steep seas, likely a times approaching square seas with
heights in feet equaling the period in seconds. Overall wave heights
decrease over the weekend into the first part of next week with much
lower wind-wave component.
PZ...Small Craft Advisory for winds from 11 AM Wednesday to 5 AM PDT
Thursday for Coastal Waters from Cape Shoalwater WA to
Cascade Head OR out 60 nm.
Small Craft Advisory for winds until 5 AM PDT Thursday for
Coastal Waters from Cascade Head OR to Florence OR out 60
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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.