Heat in Oregon, August 11 to 14, 2016

Area Forecast Discussion
National Weather Service Portland OR
245 PM PDT Thu Aug 11 2016

.SYNOPSIS...A ridge of high pressure will move over the area Friday
and Saturday. This will bring clear skies and hot afternoon
temperatures to inland locations. As the flow turns onshore Sunday,
more seasonal weather returns with areas of morning clouds, afternoon
sunshine, and near normal August temperatures. This pattern persists
into Tuesday. Thereafter, upper high pressure builds over the eastern
Pacific for dry conditions and above average temperatures.

&&

.SHORT TERM...Tonight through Sunday...A strong upper ridge around
134W moves eastward tonight and Friday. By Saturday morning the ridge
axis is losing amplitude and over central OR-central WA, with the
flow aloft becoming more west/southwest. Models indicate a weak
thermal trough forming over western OR-western WA Friday...remaining
into Saturday...and then becoming focused east of the Cascades around
00Z Sunday. Max temperatures Friday will peak about 15 degrees above
seasonal normals. Saturday temperatures will approach Friday's
values, with the limiting factor being determined by the eastward
reposition of the thermal trough. If it lingers west of the Cascades,
Saturday could be as warm as Friday, but best bet at this time is for
1-3 degrees of cooling. While temperatures are marginal (low to mid
90s), given the two-day duration and relative scarcity of 90 degree
days so far this summer (six thus far), it seemed prudent to issue a
Heat Advisory for the Willamette Valley, Portland/Vancouver metro,
and central to western Columbia River Gorge for Friday and
Saturday.

On Sunday, a weak shortwave approaches from the west while the
onshore/nwly surface pressure gradient increases. Should be a classic
summer day over most of CWA with morning clouds, particularly over
the Columbia River Basin and northern Willamette Valley, persisisting
at the coast but becoming sunny inland with an afternoon northwest
breeze. As the upper trough approaches could see enough mid-level
moisture increase in the far southern reaches of the CWA for an
isolated afternoon thunderstorm southeast tip of Lane County
Cascades. Bright

&&

.LONG TERM...(Sunday night through Thursday)...The upper level
trough looks to push east of the Cascades by early Monday as weak
upper level ridging builds into the region. This will keep dry
weather and above average temps across the forecast area through the
long term forecast.

The one thing that could throw a kink in the forecast is the
potential for a broad upper level trough to develop over the Pac NW
on Tuesday or Wednesday which could help keep clouds along the
coast. Otherwise, impacts look to remain minimal. /64

&&

.AVIATION...Skies have cleared across the forecast area as high
pressure aloft strengthens over there region, resulting in a
stable and drying air mass. Low stratus along the coast has also
cleared north of KTMK, but remains along the central Oregon coast,
particularly KONP where 200 ft cigs persist. Breezy N winds
continue along central coast through the evening. Expect VFR
under clear skies through the period for the interior. Marine
layer likely maintains or returns LIFR cigs to the southern
coastal areas (including KONP)this evening through much of the
overnight period. Confidence a bit lower for the northern coast
near KAST where model guidance suggests more offshore flow may
develop to push marine stratus back offshore.

KPDX AND APPROACHES...VFR under clear skies through the period. NW
surface wind around 10 kt, becoming light/variable overnight. Cullen

&&

.MARINE...High pressure over the waters will maintain another day
of a seasonally typical pattern of gusty N winds over the waters,
particularly south of Cascade Head. Again expect some localized or
brief gusts 20 to 25 kt between Cannon Beach and Cascade Head, and
perhaps a bit further north well offshore (beyond 40 nm), but
these will not be widespread in terms of area or time, so will
maintain the current SCAs for Wind as they are. The general
pattern remains in place through early next week, but winds on
Friday afternoon/evening might be just a bit lighter as offshore
high weakens slightly. However, a return of advisory strength
winds over the weekend appears likely. Seas remain generally 5 to
6 feet through the weekend, with dominant period remaining short
(7 to 9 seconds) as a combination of wind wave and a NW swell
component being generated off Vancouver Island impact the waters.
Cullen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory from noon Friday to 6 PM PDT Saturday for Central
     Columbia River Gorge-Central Willamette Valley-Greater
     Portland Metro Area-South Willamette Valley-Western
     Columbia River Gorge.

WA...Heat Advisory from noon Friday to 6 PM PDT Saturday for Central
     Columbia River Gorge-Greater Vancouver Area-Western
     Columbia River Gorge.

PZ...Small Craft Advisory for winds until 2 AM PDT Friday for Waters
     from Cascade Head to Florence OR from 10 to 60 nm.

     Small Craft Advisory for winds until 10 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.