Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 300429
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
929 PM PDT Wed Jun 29 2016

.SYNOPSIS...Temperate weather will continue for the next several days
across southwest Washington and northwest Oregon. Coastal low clouds
will spread locally inland each night, generally clearing back to
the coast by midday each day. A little light rain or drizzle may
fall out of the marine layer, mainly along the coast...but some
morning drizzle is possible inland as well by this weekend, as weak
upper level disturbances clip by to our north. Temperatures are
expected to remain within a few degrees of seasonal normals through
at least the 4th of July.

&&

.UPDATE...Tonight should end up looking very similar to last night,
although at the current time much of the coast has temporarily
cleared out with the exception of areas from Clatsop County north.
East-west gradient is impressively strong so marine layer should have
no trouble pushing inland and most, if not all, of the area west of
the Cascade foothills will likely wake up cloudy Thursday morning.
The tighter gradient also means some breezy winds in the valley this
evening and extending into the overnight hours with temperatures
quickly cooling. Temperatures under the clouds will drop into the 50s
but any places which manage to remain clear, like Florence Wednesday
morning, will drop into the 40s by daybreak. Only changes with the
evening forecast update were to increase morning clouds in the south
valley and add some patchy drizzle to the lower Columbia and north
valley, the same places which saw a tiny bit of drizzle Wednesday
morning. Bowen

.SHORT TERM...Previous discussion...(Today through Saturday
Night)...Inland stratus has been slow to erode in the northeastern
Willamette valley. By 23Z, expect stratus to dissipate everywhere
except for right along the coast near Astoria. Marine stratus push
tonight will be even more aggressive than last night as the AST to
PDT gradient is already >10mb and will likely top out >12mb this
evening. This is supported by 12Z NAM which fills the entire valley
with stratus tonight. Expect the stratus to clear in a similar
pattern as today with the foothills of the Cascades east of PDX being
the last to clear. The only difference will be coastal areas where it
is unlikely to clear out as it did today.

Inland stratus penetration will be less intrusive on Friday morning
as winds briefly turn southerly and pressure gradients relax. Inland
stratus will be quite extensive Saturday morning as a weak
disturbance moves through.

Given drizzle was observed this morning along the coast, and even in
a few inland locations this morning, expect drizzle most mornings
from now through the weekend. By this weekend, passing waves may
provide just enough weak forcing for drizzle or light rain warranting
a slight/low chance PoP mainly in the north Coast Range this weekend.
/Bentley


.LONG TERM...No Changes. Previous discussion follows...Very little
change as we move from the short term and into the long term with
morning clouds and afternoon sun. Given climo PoP of less than 15
this time of year, have kept all periods after 00Z Monday dry for now
as model uncertainty increases and we remain on the far southern edge
of any disturbances which may pivot through the flow. /Bentley

&&

.AVIATION...An upper level trough will result in a deeper marine
layer tonight and support another inland marine push Thursday
morning for widespread MVFR cigs. Onshore gradients continue to
increase as an indication of another good inland surge of stratus
tonight. Models indicate that clouds will reform along the
Cascade slopes and fill in to the Willamette Valley during the
night. This may occur earlier than previous forecast indicated as
satellite imagery shows stratus already reforming along the
Cascade foothills. MVFR cigs along the coast will likely lower
to IFR 10z in the north. Stratus did burn back offshore more
along the central coast of Oregon this afternoon but satellite
imagery shows stratus reforming along the coast south of Newport
and expect IFR cigs to develop after 06z. Models agree that a
weak upper ridge will move in Thursday afternoon which will likely
result in slightly early clearing...especially inland tomorrow
with VFR conditions after 18-20z inland. However, the south WA
and north OR coast may keep MVFR cigs for most of Thursday.
Schneider

KPDX AND APPROACHES...VFR conditions this evening. MVFR cigs will
return tonight between 07z and 09z with clearing expected around
20z Thursday. Schneider

&&

.MARINE...High pressure offshore continues to exert a strong
NW onshore gradient across the waters. Have extended the Small
Craft Advisory until 11pm for the near shore waters south of
Cascade Head and will continue for the adjacent offshore waters. A
persistent summer-time pattern of high pressure over the WA and
OR waters with a thermal low over California continues most of the
week for northerly winds that increase in the afternoon and
evenings. Two weak disturbances will weaken this pressure pattern:
A weak front on Friday, and a weaker boundary on Sunday. The winds
will become light during these periods and briefly back to the
west or south. The seas are mainly a mixture of steep wind waves
and a small fresh swell, although a small background long-period
south swell may become more noticeable during the periods of
lighter winds (Fri and Sun). The seas will generally hover between
3 and 5 ft with occasional rises to 6 ft into next week.
TJ/Schneider

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 2 AM PDT Thursday for
     Waters from Cascade Head to Florence OR from 10 to 60 nm.

     Small Craft Advisory for winds until 11 PM PDT this evening for
     Coastal waters from Cascade Head to Florence OR out 10 nm.

&&

$$

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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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