Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 280558 AAA
Area Forecast Discussion
National Weather Service Portland OR
1059 PM PDT Fri May 27 2016
Corrected days of the short term.
.SYNOPSIS...Low pressure will persist around southern B.C. through
the weekend, with onshore flow and plenty of clouds in southwest
Washington and parts of northwest Oregon, brushing the northern
areas with a bit of moisture at times this weekend. Upper level
ridging will build in Sunday night and on Memorial Day for drying
weather with less clouds and warmer daytime temps, with highs on
Tuesday and Wednesday expected to reach into at least the mid 80s
inland. Temps cool a bit late next week, and a threat for showers
or possibly even thunderstorms returns as an upper level trough
approaches the coast, though there is some disagreement amongst the
models for late next week.
.SHORT TERM...(Tonight through Memorial Day)...An area of low
pressure will continue along the central and southern B.C. coast
through the weekend, maintaining onshore flow and lots of clouds
across southwest Washington and much of northwest Oregon. This will
also send some precipitation into the area at times, especially
across the north.
Showers from this afternoon are winding down this evening much as the
models are showing, with just a few left in the northern Cascade
forecast zones. There is an area of more layered and cooler topped
clouds off the Washington coast that will spread onshore late tonight
and Saturday across western Washington and clipping far northwest
Oregon. The models show this as an area of light warm advection and
isentropic lift, somewhat like we can get in winter but weaker. It
appears we will get some light more stratiform like rain or drizzle
from this on Saturday, with the best chance of precipitation along
the north coast and adjacent coastal mountains, and possibly trying
to leak over into the south Washington Cascades. There is some small
chance of light precipitation along I-5 from Portland north to Kelso
and Castle Rock, with the better chance farther north.
The trailing weak cold front, if you can call it that, appears to
drag through the northern areas Saturday night into early Sunday with
a bit of light stratiform precipitation again across the far north.
Look for temps a bit warmer into the 60s over the weekend, but still
struggling to reach seasonal normals.
An upper ridge is forecast to build into the Pacific Northwest Sunday
night and Monday, which should bring clearing skies and more sunshine
on Memorial Day. Look for temps to rebound well into the 70s on
.LONG TERM...No Changes. Previous discussion follows...
Monday night through Friday...An amplifying upper level ridge looks
to persist over the Pac NW through at least Wednesday bringing dry
weather and warmer temperatures. Models continue to suggest 850mb
temperatures near 15-20C early next week under moderate offshore flow
so will continue the upward trend with the temperature forecast. As
of now, it is becoming more likely that we could see the warmest
temperatures of the year next week with afternoon highs on Wednesday
approaching 90F. Models then start to diverge for the latter half of
the workweek. The ECMWF remains a little more progressive than the
GFS late next week and shows a meandering cutoff low developing late
Thursday/Friday over southern Oregon. If the ECMWF is correct we
could see some showers develop across the CWA. As such, will maintain
slight chance PoPs and cooler temperatures in the forecast, but
confidence remains extremely low. /64
.AVIATION...VFR conditions expected through the TAF period at all
sites. Occasional MVFR cigs were observed with the heavier rain
showers this afternoon, but these have become less frequent as the
showers have diminished this evening. With a lull in activity
expected overnight, do not expect showers to impact any of the
PDX AND APPROACHES...VFR conditions expected through the period.
Light and variable winds through mid day tomorrow. A few scattered
showers will be around later tomorrow afternoon, but there is a less
than 25 percent chance that PDX is impacted. /Bentley
.MARINE...WNW winds will shift more westerly over the next 6 hours
and eventually southwesterly Saturday morning ahead of an approaching
weak front. Winds will increase for 6-9 hours ahead of the front with
gusts approaching small craft criteria in the northern zones for
several hours. Given the stronger winds will mainly be north of our
forecast area, will hold off on a SCA for winds at this time, but one
may be needed if winds are stronger with later forecast guidance.
Otherwise, winds will remain in the 10 to 15 kt range into early next
week. Northerly winds begin to increase Monday night as a thermal low
develops northward along the coast.
Seas will remain in the 4 to 6 foot range through the next 7 days
without much of a catalyst for higher seas. Given seas and normal
ebbs, expect favorable conditions in the Columbia River bar through
the period. /Bentley
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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.