Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 281542
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
841 AM PDT Sat May 28 2016

.SYNOPSIS...An upper level low pressure system over southern BC
will persist through Sunday 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 start to build Sunday night, then
strengthen Memorial Day and Tuesday, resulting in much warmer and
drier conditions. Daytime temperatures are expected to cool a bit
late in the week.
&&

.SHORT TERM...(Today through Memorial Day)...Minimal changes to the
current forecast. Water vapor satellite imagery this morning had a
broad upper low draped across Vancouver Island and Southern British
Columbia. A couple of weak disturbances within West to Northwest flow
aloft are expected to impact the forecast area through the weekend.
One such feature is tracking south along the Southern British
Columbia coastline. KLGX and KRTX doppler radars show precipitation
activity across SW Washington and far NW Oregon as of 15Z. The 06Z
GFS and 12Z NAM indicate decent isentropic lift along the 290K
surface this morning, primarily focused over SW Washington and
extreme NW Oregon. Isentropic lift gradually lifts north this
afternoon. However, low-level onshore flow will persist today through
Sunday, resulting in a marine layer up to at least 6000 feet MSL.
Models show an ill-defined cold frontal feature over Western
Washington this afternoon, sliding south late in the day through this
evening. Precipitation with this feature looks to be focused north of
a Tillamook to Mt. Hood line. However, as the marine layer gets
reinforced tonight, cannot rule out areas of drizzle or light rain
further south along the coast and west slopes of the Oregon Coast
Range.

Moist low levels persist Sun, as the main upper trough axis moves
across the area. NAM time-height section for KPDX shows considerable
moisture below 800 mb or so Sun morning, then some drying in the
lowest levels. Expect gradual improvement across the area Sun
afternoon as the surface flow turns more out of the north. Sun night
should see good radiational cooling as the air mass continues to dry.
NAM hints at some morning low clouds Mon morning in the SW Washington
interior valleys and the North Oregon coast and coastal valleys with
the surface ridge axis near the Columbia River. GFS 850 mb temps warm
from a range of +5-10C Sun to +10-15C Memorial Day. Weishaar

.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...Expect widespread VFR conditions through this
afternoon. The north coast and coast range will remain mostly
cloudy with occasional showers. There will be more sun the
further south and east you go. Clouds will slowly increase inland
later this afternoon as a weak front approaches, with cigs developing
around 4500 to 6000 ft. Onshore flow will strengthen later today
and tonight, with 2500 to 3500 ft cigs increasing along the coast
this evening, then pushing inland overnight.

PDX AND APPROACHES...VFR with northwesterly flow aloft, with
light onshore flow at low levels. Ceilings around 4500 to 6000 ft
will develop later this afternoon. Onshore flow to increase
tonight, bringing 2500 to 3500 ft cigs in overnight. Pyle

&&

.MARINE...Breezy southwest winds expected today as a weak cold
front pushes into the waters, but they should remain below small
craft advisory thresholds. 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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