Funnel Cloud in Oregon, May 19, 2016

Area Forecast Discussion
National Weather Service Portland OR
152 PM PDT Thu May 19 2016

.SYNOPSIS...An upper level low pressure storm system will linger over
the region through early next week. This will result in mostly cloudy
skies, cool temperatures and off and on showers most days.

&&

.SHORT TERM...Today through Sunday...A cool upper level trough is
currently dropping southward across the Pacific Northwest. An
unstable northwesterly flow pattern is currently bringing widespread
showers to northwest Oregon and southwest Washington today.
Convection so far has remained shallow, but with some sunbreaks,
temperatures approaching 60F across portions of the Willamette Valley
may allow for showers to intensify enough to produce some hail and
possibly a rumble of thunder or two later this afternoon and early
this evening. Shower coverage and intensity should generally decrease
later this evening as surface heating wanes.

With that said, shower activity is most prevalent across western
Washington and off the Washington coast early this afternoon. This
area of showers is likely associated with an area of -26 to -28C
500mb temperatures, which is expected to shift southward across far
western Oregon and the coastal waters late this afternoon and this
evening. As a result, shower coverage and intensity will likely hold
on longest near the coast and across our far southern zones
overnight.

As the upper level low pressure shifts south of the region late
tonight and Friday, warmer and drier air aloft from the north and
east should work its way overhead. This should help to limit shower
coverage and intensity Friday afternoon and evening. The Coast Range
and Cascades will stand the best chance of a few showers developing.

Discrepancies between models in rain chances continue to exist for
Saturday. Low level westerly flow will certainly keep rain chances
going across the Coast Range and particularly the Cascades on
Saturday. A 700mb closed low pressure is forecasted to move into west
central Washington, which may bring an area of steadier precipitation
to the south Washington Cascades and far north Oregon Cascades late
Saturday, but confidence this area will actually be affected remains
low.

Models continue to suggest a shortwave trough wrapping around the
parent low pressure will likely increase shower coverage Sunday so
PoPs were nudged upwards during this period. /Neuman

.LONG TERM...Sunday Night through Thursday...Showers appear likely to
linger across portions of northwest Oregon and southwest Washington
early next week as the upper level low pressure currently residing
over the Pacific Northwest slowly shifts south and east of the
region. Most recent model solutions suggest weak shortwave ridging
should slowly build over the Pacific Northwest towards the middle of
next week, but some model solutions continue to suggest weak upper
level troughing will persist over the region. Due to the uncertainty,
slight chance to low end chance PoPs and near average temperatures
were kept in the forecast. /Neuman

&&

.AVIATION...Low pressure and a moist/unstable air mass will
continue to bring showers to the forecast area through this
evening. Conditions will be predominately VFR, but expect some
MVFR cigs/vis in heavier showers. There is also a slight chance of
thunder/lightning into the early evening hours. The heavy showers
may also cause mountain obscurations in the Cascades into the
early evening.

KPDX AND APPROACHES...Primarily low-end VFR conditions expected
through the evening with some brief periods of MVFR cigs in the
2500 ft range with heavier showers. There is also about a 20
percent chance of thunder this afternoon...but confidence low in
thunder threat unless we get some sun breaks.

&&

.MARINE...Strongest winds will be in the outer waters through the
evening with winds in the 15-20 kt range and gusts around 25 kts.
In the inner waters...gusts up to 20 kts expected through the
evening. Lighter winds of 10 to 15 kts are expected Friday.

Seas will also run around 10-11 ft in the outer waters and around 9
ft in the inner waters tonight. Seas and winds will decrease
slightly later tonight into Friday. The elevated seas will also
produce rough conditions on the Columbia River Bar during the
ebbs.

Little change expected in the overall pattern through early next
week. Broad low pressure will persist near the Pac NW, with strong
high pressure well offshore. At this point it appears the
strongest winds will remain in the Offshore Waters this weekend. A
decent fetch along the BC coast will initially keep seas in the
8-10 ft range through Friday night, then seas are expected to
subside as winds ease in the fetch area.  tw/Weagle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 9 PM PDT this evening
for Waters from Cape Shoalwater WA to Florence OR from 10 to 60
nm.

     Small Craft Advisory for hazardous seas until 6 AM PDT Friday
     for Waters from Cape Shoalwater WA to Florence OR from 10
     to 60 nm.

     Small Craft Advisory for Rough Columbia River Bar until 6 PM
     PDT this evening.

     Small Craft Advisory for Rough Columbia River Bar from 3 AM to
     8 AM PDT Friday.

&&

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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.