Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 280915
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
215 am PDT Sat May 28 2016

.SYNOPSIS...An upper level low pressure system over southern BC
will persist through the weekend bringing onshore flow to southwest
Washington and parts of northwest Oregon. This will keep a chance
for some precipitation across the northern parts of the forecast
area. Upper level ridging will build in Sunday night and on Memorial
Day for drying weather with decreasing clouds and warmer daytime
temps. Temps are expected to cool a bit late next week, and a threat
for showers or possibly even thunderstorms returns as an upper level
trough approaches the coast.
&&

.SHORT TERM...(Tonight through Memorial Day)...A trough of low pres
was over southern BC early Sat morning. A shortwave digging down
from the northern BC coast will swing across southern BC and WA Sun.
Models in good agreement showing a weak warm front off the WA coast
this morning, lifting ne during the day. moist isentropic lift is
depicted between 285k and 290k isentropes during the morning,
generally limited to north of a line from ktmk to kspb. onshore flow
persists mainly n of that line into the afternoon which is roughly
the axis of the surface ridge, and keeping atmosphere moist below
about 700 mb. As a weak cold front follows late in the day sinking
into the n part of the forecast area, necessitating a chance for
showers in the north through the afternoon and evening. Moist low
levels persist into Sun, as the main upper trough axis moves
through. With better dynamics extending further s, chances for
showers will extend a little further s Sun than today. Chances for
showers will drop off Sun afternoon and evening as the upper trough
begins to move e, and low levels start to dry as the flow turns more
northerly. Models moderate 850 mb temps several degrees today as
heights rise, in turn moderating high temps closer to seasonal
normals today and Sun.

Sun night and Mon as the upper pattern shifts e and a ridge of high
pres begins to move in over the Pacific NW. Low level flow turns
offshore for a return to dry weather with decreasing clouds and
temps warming back above normal.

.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...Areas north of a Newport to Salem will remain under
plenty of clouds with along with a few showers. Ceilings generally
6000 to 8000 ft this am with a few pockets of MVFR along the
coast, but ceilings will lower a bit more this afternoon. However,
areas to the south will see mix of clear skies and clouds, though
clouds will be increasing as the day progresses. Onshore flow will
strengthen later today and tonight, with 2500 to 3500 ft cigs
increasing over most of northwest Oregon after 02z.

PDX AND APPROACHES...VFR with northwesterly flow aloft, with
light onshore flow at low levels. Ceilings around 7000 to 8000 ft
this am will gradually lower a bit more through this afternoon,
but remain in 4500 to 6000 ft range.                 Rockey.
&&

.MARINE...as weak front drops into the region today, will see
winds turn more southwest to westerly this am. Once the front
moves onshore later today and early this evening, winds will
becoming west to northwesterly. But, winds will remain 15 kt or
less. Overall, seas running 3 to 4 ft today and tonight.

On Sunday, high pressure will spread across the coastal waters,
and remain well into next week. At same time, thermal low pres
over northwest Calif and southwest Oregon will strengthen. This
will bring typical June pattern for Mon through Wed, with gusty
north to northwest winds of 15 to 25 kt, with strongest south of
Cascade Head. Strongest winds will be in afternoons/evenings.
Also, with these winds will come choppy wind-driven seas, with
overall, combined seas (wind waves and swell combined) running 5
to 8 ft, with highest seas south of Cascade Head.
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&

$$

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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.



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