Area Forecast Discussion
Issued by NWS Portland, OR

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648
FXUS66 KPQR 251626
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
923 AM PDT Sun Jun 25 2017

.SYNOPSIS...High pressure over the Pacific Northwest will continue
the very hot temperatures across much of northwestern Oregon and
southwestern Washington. A southerly marine surge will be working up
the coast early today, then extend inland late Sunday bringing much
cooler temps on Monday. There is a slight chance for some high-based
thunderstorms over the portions of the forecast area on Monday. Dry
northwesterly flow sets up later this week across the region,
bringing more seasonable temperatures and a pattern of morning
clouds and afternoon sunshine.

&&

.SHORT TERM...Today through Wednesday...A cooler day for much of the
area but another hot day across much of the interior valleys and
Cascades.  The thermal trough lay along a northwest-southeast line
from the east slopes of the north Oregon coast range ton the Lane
county Cascade foothills. For example temperatures in eastern
Washington and Yamill counties are in the mid to upper 70s as of 8
am, while the south Willamette valley in the mid 60s to low 70s as
cooler marine air seeped inland overnight. The thermal trough will
slowly shift east today but much of the interior valleys will near
100 degrees again. The south Willamette valley will be warm but about
10 degrees cooler than the north Willamette valley. Higher pressure
east of the Cascades is spilling through the Columbia River Gorge
toward the thermal trough resulting gusty east winds at the west end
of the Gorge.  On the coast however onshore flow is bringing cooler
weather.  Satellite imagery reveals that a southerly surge of marine
stratus has continued to move north, just offshore,  along the Oregon
coast and is now just off the Long Beach peninsula. Expect the
stratus to push in to the immediate coastline again by late morning,
especially in the south (such as at Newport and Florence) where
latest observations suggest increasing onshore flow may push more of
this stratus back onto the coast shortly after sunrise.

The current Heat Advisory and Excessive Heat Warning headlines for
the northern half of the CWA and the Cascade foothills
therefore remain unchanged. The thermal low pressure will shift east
of the Cascades by later tonight, and will result in the entire
forecast area cooling considerably by Monday.

As the upper ridge bringing the heat shifts east, a weak upper level
impulse lifting northeastward into northern California and Oregon
Sunday night and Monday will help to destabilize the atmosphere is it
brushes our southern forecast area. At this point, it appears there
is a chance of thunderstorms grazing primarily the Lane and Linn
County Cascades, but perhaps also the central Oregon coast and maybe
the southern half of the interior lowlands. These will be elevated
thunderstorms, so we`ll need watch for changes to the
instability/moisture moving from the south into the region to expand
or cut back on the thunderstorm coverage. Not much change to the
pattern from Tuesday into Wednesday, with morning clouds giving way
to afternoon sunshine and seasonable temperatures.

.LONG TERM...No Changes. Previous discussion follows...Wednesday
night through Sunday...Low level onshore flow will continue through
much of the long term period. Models continue to show a broad upper
level trough moving across the forecast area late Tuesday/Wednesday
which will bring an increase in cloud cover along, with some patchy
morning fog or drizzle on the north coast. Expect much more seasonal
temps on Wednesday afternoon. Upper level ridging will start to build
over the Pac NW late next week which will bring slightly warmer
temps. The good news is that the ridge will not be as strong next
week which will prevent temps from
becoming outrageously hot. /64

&&

.AVIATION...Widespread VFR conditions in place this morning with
high pressure aloft. However, a thermal trough will gradually
push inland through the day, bringing increasing onshore flow.
Visible satellite imagery shows a marine stratus deck just
offshore. The clouds will bring IFR cigs, with potential for vsby
restrictions in fog into the coastal TAF sites by midday. The
onshore flow increases tonight, and is expected to bring MVFR
stratus into the interior lowlands. The clouds will reach the
southern Willamette Valley first, and may arrive by late this
evening. The clouds should then overspread the rest of the
interior TAF sites overnight. East surface and low-level wind to
continue in the Western Columbia Gorge through early this
afternoon afternoon, then weaken as the surface thermal trough
migrates toward the Cascades. An approaching upper level trough
will bring a slight chance for elevated thunderstorms late
tonight and tomorrow morning, with the best chances over the
southern Willamette Valley and Lane County Cascades.

KPDX AND APPROACHES...Expect VFR conditions through tonight. W
to NW surface wind at the terminal will increase late this
afternoon as onshore low-level flow strengthens. MVFR stratus
likely to arrive between 12Z-15Z Mon. Pyle

&&

.MARINE...High pressure over the northeast Pacific will continue
well into next week. South to southwest wind will spread through
the waters today. However, north wind expected to prevail over
the outer northern waters through Mon morning.

Typical summer north wind over the waters Mon afternoon through
at least late next week. There will be periods of small craft
advisory wind speeds, primarily Tue and Wed afternoons and
evenings. Models show the high pres weakening late next week.

Seas to continue well below 10 ft for the next several days.
There is the potential for another uni-wave set-up Tue and Wed.
Overall, despite fairly low wave heights, the pre-dominant wind
wave component will make for steep and choppy conditions.
Pyle/Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning until 9 PM PDT this evening for Western
     Columbia River Gorge.

     Heat Advisory until 9 PM PDT this evening for Cascade Foothills
     in Lane County-Central Columbia River Gorge-Central
     Willamette Valley-Greater Portland Metro Area-Lower
     Columbia-Northern Oregon Cascade Foothills.

WA...Excessive Heat Warning until 9 PM PDT this evening for Western
     Columbia River Gorge.

     Heat Advisory until 9 PM PDT this evening for Central Columbia
     River Gorge-Greater Vancouver Area-I-5 Corridor in Cowlitz
     County-South Washington Cascade Foothills.

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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