Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland
941 am PDT sun may 24 2015
Synopsis...an upper level low will move slowly from southern b.C.
Today across eastern Washington Monday and into Idaho later Tuesday
and Wednesday. This will maintain the low level onshore flow across
southwest Washington and northwest Oregon for the next several days
with little or no clearing in the afternoons. It will also provide
the possibility of some night and morning drizzle over the area...as
well as a few late day showers in the higher Cascades. An upper level
ridge will move into the Pacific northwest during the second half of
the week...weakening the onshore flow and allowing more sunshine to
break through with warming temperatures.
Short term...we are seeing a near repeat of the last few days as
cloudy conditions cover southwest Washington and northwest Oregon
with areas of drizzle mainly near the coast and in the mountains.
Onshore flow continues to be moderately strong as another low is in
southern b.C. However...this has turned the winds aloft to more west
and northwesterly as well...reinforcing the onshore flow but also
bringing an end to the easterly flow and the associated showers. If
any showers develop today it will be near the crest of the South
Washington Cascades due to flow around the southern b.C. Low.
Temperatures today might creep up a couple of degrees from the last couple
of days...but still stay in the low to middle 60s as clouds stay
The southern b.C. Low will drop into central and eastern Washington
on Monday...maintaining the strong onshore flow and the possibility
night and morning drizzle around the area. Believe the clouds will
have a tough time again breaking up Monday...with temperatures staying in
the low to middle 60s. With the low centered in central and eastern
Washington...we may see our northern Cascades zones clipped by a few
showers in the flow on the backside of the low.
The low is moving into Idaho by later Tuesday. The onshore flow
should continue...though we might see a few sun breaks late in the
day and in the evening. The bit more sunshine in the higher Cascades
continued with the return flow on the back side of the low will
maintain a chance of late day showers near the crest of our northern
Cascade zones. Tolleson
Long term...no changes. Previous discussion follows...
Tuesday night through Saturday...continued onshore flow behind the
Monday system will keep cool cloudy weather through Wednesday. Most
precipitation should stay up in the higher elevations of the
Cascades. Brought temperatures back down some through the end of the week as
models are now showing the region staying under weak onshore flow.
Temperatures do warm some Thursday-Sat as shortwave ridging moves over the
region. A thermal low to our south will set up a good pattern for dry
weather for the Willamette Valley...with clearer skies in the
afternoon...and afternoon showers and possibly thunderstorms in the
Aviation...expect a near repeat of the last 24 hours. Marine layer
will remain in some form for the next 24 hours but do stand a better
shot at notable inland cloud breaks late this afternoon/early
evening. MVFR ceilings at the coast for the day although do see hints in
models at konp breaking free for a few hours similar to Saturday.
MVFR ceilings inland this morning will lift to a VFR ceiling somewhere
between 21-23z. May actually get enough mixing to see the deck
scatter out late this afternoon or early evening for a few hours
before filling back in shortly after sunset. Ceilings fall back down to
MVFR around 025 tonight...with IFR ceilings and visibility possible along the
coast after 25/06z.
Kpdx and approaches...MVFR ceilings around 025 through about 22z. Will
see the deck lift to between 035 and 045 perhaps opening the door to
a period of visual approaches in the 25/00-04z time frame. MVFR ceilings
around 020 likely after 25/09z. /Jbonk/64
Marine...no significant changes...previous discussion follows. High
pressure remains offshore with low pressure over the inland Pacific northwest for the
next several days. This will continue to bring benign conditions to
the waters with northwest winds generally below advisory criteria. There is
a chance for some advisory gusts above 21 knots sun and Monday afternoon
and evening south of Newport...but confidence is not high that it
will come to fruition. Stronger winds off the b.C. Coast are
producing a fresh swell out of the northwest and will continue to bring
choppy seas through at least Tuesday. /64
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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.