Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 271221 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
521 AM PDT Tue Jun 27 2017

.SYNOPSIS...Dry northwesterly flow across the region persists with
broad upper level high pressure over the eastern Pacific. A weak
ridge moves across the Pacific Northwest later in the week, for
slightly warmer temperatures across the region. A few upper level
disturbances may deepen the marine layer later in the weekend, but
generally seasonable temperatures continue through early next week.

&&

.SHORT TERM...Today through Friday....Latest satellite imagery and
surface observations reveal a rather extensive layer of marine
stratus across most of the forecast area early this morning. Expect
this trend to continue, with overcast skies for all of the forecast
area below around 5,000 feet elevation. While some of the model
guidance continues to suggest a very rapid clearing after sunrise
today, have continued to indicate a somewhat slower retreat of the
marine layer in the forecast. Based on the depth of the layer, expect
that it might be closer to midday or even early afternoon before
skies become primarily sunny. This additional cloud cover may keep
high temperatures a few degrees cooler than yesterday, but still
generally near climatological normals.

For the next few days, expect little change to the general pattern,
as a broad upper level ridge remains in place across the far
northeastern Pacific and into the Pacific Northwest. This will
maintain the trend of morning clouds giving way to afternoon sunshine
and will maintain temperatures close to normals.

By Thursday, the offshore ridge migrates a bit closer to the region,
which will weaken the onshore surface pressure gradients. This will
ease the strength of the marine push for less widespread clouds and
somewhat warmer temperatures Thursday and Friday. Expect afternoon
highs in the lower 80s across the interior lowlands and in the mid
60s along the coast.   Cullen

.LONG TERM...Friday night through Tuesday...Weak onshore low-level
flow continues over the weekend, maintaining cool and generally
cloudy conditions along the coast. Expect that the onshore gradient
will be insufficient for widespread marine stratus intrusion into the
interior. Thus, abundant sunshine and a slightly warmer air mass will
push afternoon temperatures into the lower to mid 80s across the
Willamette Valley. There is general agreement among the model
guidance that a series of shortwave disturbances will track into
southern British Columbia or western Washington over the weekend and
early next week. The first is expected to arrive late Saturday or
early Sunday, though some differences remain with respect to the
strength and placement of the impulse. Nevertheless, expect that it
will be close enough to the forecast area to bring a stronger onshore
gradient, more widespread cloud cover, slightly cooler temperatures,
and perhaps some light precipitation to the region. The subsequent
shortwave likely follows a similar track and moves into the Pacific
Northwest around Monday. Therefore, expect little change, with rather
seasonable temperatures and morning clouds giving way to afternoon
sun for the extended holiday weekend.  Cullen

&&

.AVIATION...Onshore low level flow will continue through
Wed bringing a marine influence to the area. Inland, expect MVFR
cigs through the morning before lifting to VFR in the afternoon.
MVFR cigs return inland late tonight into Wed morning. Coastal
areas will continue to be MVFR today and tonight but there may be
spots of IFR cigs through midday. Low MVFR to IFR cigs return
tonight into Wed morning.

KPDX AND APPROACHES...MVFR cigs around 2500-3000 ft, lifting to
VFR 4500-5000 ft around midday, the likely becoming CLR to SCT
5000 ft during the afternoon and evening. MVFR cigs return late
tonight, after 10Z at about 2000-2500 ft.

&&

.MARINE...High pressure offshore will bring northwesterly and
northerly through the week. The winds may come close to Small
Craft Advisory thresholds during the afternoon and evening on
Tuesday and Wednesday mainly in the far outer waters, but it
looks very borderline at this time.

Seas to continue below 10 ft for the next several days. Seas are
around 5 to 6 ft with a 7 to 9 second dominant period. Seas will
be somewhat choppy but does not look like it will exceed
advisory criteria. Periods will lengthen a bit later in the week.
/mh

&&

.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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