Area Forecast Discussion
Issued by NWS Portland, OR

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647
FXUS66 KPQR 172115
AFDPQR

Area Forecast Discussion
National Service Portland OR
215 PM PDT Sat Aug 17 2019

.SYNOPSIS...After today`s marine push of cooler air and partly to
mostly cloudy conditions, temperatures will warm slowly but steadily
through Tuesday. A weakening cool front will approach the coast
Wednesday afternoon, bringing increasing clouds, cooler air, and a
slight chance of showers Wednesday night or early Thursday. The end
of the week looks dry, with morning clouds and daytime temperatures
near normal.

&&

.SHORT TERM...Tonight through Wednesday...A fairly uneventful pattern
for the next several days in terms of sensible weather. The Rex block
over the Pacific begins to break down, with the upper high over the
Aleutian Islands and Bering Sea retrograding, and the persistent
upper cutoff around 42N/160W moving slowly eastward. This cutoff is
eventually entrained by an upper trough dropping southward over the
Gulf of Alaska. Heights build over the PacNW in advance of this
system, with temperatures peaking on Tuesday several degrees above
normal. As the aforementioned upper trough and its surface low move
into the central BC coast Wednesday, a decaying cold front will drag
across the PacNW late Wednesday or Wednesday night. At 18Z
Wednesday, ensemble mean IVT is a not-too-shabby (for August) 350-
400 kg/m/s over the eastern Pacific as the front approaches the
OR/WA coast, but IVT quickly diminishes as low-level southerly flow
collapses in the 6-12 hours thereafter. There could be enough
lingering moisture and ascent for a slight chance of light
precipitation across southwest WA and far northwest OR, particularly
along the coast. Precipitation certainty aside, there is high
confidence of a moderate marine intrusion and seasonably cooler
airmass arriving by Wednesday evening. Bright

.LONG TERM...Wednesday night through Saturday...Following the passage
of the decaying cold front Wednesday night, onshore flow persists
through the end of the week. With the break down of the Pacific
block, westerly flow with embedded progressive shortwaves will bring
a seasonable August weather scenario for the end of the week. The
timing of individual shortwaves will augment the morning
cloud/afternoon clearing regime, but ensemble mean heights are high
enough that precipitation appears unlikely Thursday through
Saturday. Bright

&&

.AVIATION...Moderate to strong northwesterly onshore flow
continues, with a low VFR to MVFR cloud deck lingering across the
region. This cloud shield will continue to gradually clear from
southeast to northwest through the afternoon and evening, with
clearing reaching a KONP to KMMV line around 22z. Marine stratus
likely reforms across nearly all of the forecast area tonight
after 09z-12z.

KPDX AND APPROACHES...VFR stratus will continue to slowly lift
and possibly scatter late this afternoon. Surface winds remain
light. MVFR stratus likely returns around 11z tonight. Cullen

&&

.MARINE...High pressure remains in place well offshore as thermal
low pressure persists over northwestern California and
southwestern Oregon. The surface pressure gradient isn`t
particularly strong and will maintain winds closer to 15 kt over
most of the waters, though a few gusts to 20 kt possible over the
southern and outer portions of the coastal waters.. Meanwhile,
seas holding around 6-7 feet, with a mix of a larger 8 second
and smaller 15 second swell.

Little change to the overall pattern through the start of next
week. A front will move near the waters early next week,
bringing south winds to the waters Tuesday and Wednesday. Cullen

&&

.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. This area is
commonly referred to as the forecast area.



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