Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland
241 am PDT Sat Apr 18 2015
Synopsis...high pressure will persist through Monday with
temperatures gradually warmer each day...potentially bringing the
warmest days so far this year. An upper trough may bring some showers
Tuesday afternoon and evening and cooler conditions. Wednesday should
be dry...but cloudy and cool before a series of cold fronts bring a
chance for rain and mountain snow Thursday and Friday.
Short term...today through Tuesday...high pressure is building over
the Pacific northwest this morning aloft and surface...and will hold through
Tuesday. Skies are clear early this morning...and radiation cooling
may lead to some patchy stratus/fog around sunrise along the
immediate coast and in the interior valleys. However...the atmosphere
is rather dry with temperature/dew point depressions around 10
degrees inland...and think the coast stands the best chance for some
North-northwest winds are already observed along the coast and will remain
through tonight as the high pressure settles across Oregon and
Washington and a thermal trough holds over northern California. Any
fog early this morning will quickly clear and expect temperatures to
rise into the low to middle 70s for the interior valleys and the upper
60s for the coast this afternoon.
The thermal trough will extend slightly northward and offshore
tonight allowing the inland winds to become off shore. This will
result in drier air over Oregon and Washington tonight and a lack of
fog/clouds. Sunday will possibly be the warmest day of the year so
far and expect the interior valleys to warm into the upper 70s.
The pressure pattern will change very little Sunday night and
Monday...and expect even warmer temperatures for Monday.
The ridge will shift inland Monday night as an upper trough
approaches...with onshore flow bringing cooler and moister air to
coastal regions Tuesday morning. Expect marine stratus to return to
the coast and be deep enough to move through the coastal gaps into
parts of the Willamette Valley. These clouds combined with a passing
trough will result in cooler temperature Tuesday afternoon with
inland highs back in the 60s and coastal highs in the 50s.
The upper trough may help bring some monsoonal moisture from
California and Arizona northward for some afternoon showers over the
Oregon and Washington Cascades Tuesday afternoon and possibly some
thunderstorms along the Cascade crest. However...the best chance for
thunderstorms will be east of the Cascades. Tj
Long term...Tuesday night through Friday...an upper trough will bring
a chance of showers...mainly to the Cascades Tuesday night. Wednesday
will be cloudy and cool behind the trough. A couple ofcold fronts
will increase rain and mountain snow chances for Thursday and Friday.
Aviation...high pressure with dry stable flow aloft. At 2 am...ceilings
of 800 to 1200 feet were forming along the coast. These will break
up between 15z and 18z as gusty north winds increase along the coast.
Kpdx and approaches...VFR under dry stable air mass. No adverse weather
impacts through tonight. Rockey.
Marine...high pressure over the region...with thermal low pressure over
northwest calif into far SW Oregon. This will maintain gusty north winds.
While the strongest winds on S Oregon coastal waters...should
still have gusts 20 to 25 knots north of Cascade Head...and 25 to 30 knots
to S. Also...winds will be strongest during the afternoon and
evening hours...slackening late at night. Seas generally 8 to 10
feet today and tonight...but will ease back a tad...with 6 to 9 feet
Longer range shows high pressure over the NE Pacific strengthening Tuesday and
Wednesday...with northwest winds gusting 20 to 30 knots at times.
Pz...Small Craft Advisory for winds through sun am on all waters.
Small Craft Advisory for rough Columbia River bar
conditions until 7 am today...and again 4 to 8 PM today. &&
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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.