Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 241653 CCA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
929 AM PDT Sat Jun 24 2017

.SYNOPSIS...High pressure over the Pacific Northwest will bring
unseasonably hot, potentially record breaking temperatures across
much of northwestern Oregon and southwestern Washington Saturday and
Sunday. A marine push should result in cooler temperatures beginning
late Sunday and Monday. Dry northwesterly flow sets up next week
across the region, bringing more seasonable temperatures and a
pattern of morning clouds and afternoon sunshine.

&&

.SHORT TERM...Today through Tuesday...A warm start this morning 8 am
temperatures already around 5 to 7 degrees above 24 hours ago.  The
building high pressure aloft will bring hot - potentially record
breaking - weather today for much of the forecast area. 850 mb
temperatures is forecast to rise to 21-26 C about 5 C over yesterday.
This will translate to near 100 Degress for much of the inland areas.
Even some of the coastal sites - primarily Tillamook and points
north - will be in the neighborhood of 90 degrees F.  The 12z KSLE
sounding came in with an 850mb temperature of 21C, which is in
agreement with 12Z GFS & NAM.

The thermal trough sits on the coast today giving offshore flow to
the north coast zones. The central Oregon coast may see onshore flow
earlier in the day as the thermal trough nudges inland slightly for
that area.   Air over eastern Oregon and the Columbia River Gorge
will be slightly cooler than the air residing over western Oregon so
temperatures should be slightly cooler near and within the Columbia
River Gorge on Saturday. As a result, continued the trend of keeping
the warmest temperatures in the PDX metro towards downtown and points
west and south.

No changes to the existing advisories and warnings at this time, as
the relatively dry air mass and at least some reasonable overnight
relief as temperatures drop off should prevent more widespread
issues. As discussed in the previous discussion, the Excessive Heat
Warning for the western Columbia River Gorge is due to the
combination of high temperatures AND warm low temperatures Saturday
night, where many areas within this zone will likely have a
hard time dropping below 65-70F. Such warm low temperatures greatly
increase the risk of heat related illness and stress, especially for
those without air conditioning.

Some locations in the Portland metro area closer to the gorge - i.e.,
those spots in/near Troutdale & Gresham - will likely keep sufficient
east wind Saturday night to prevent temperatures from cooling down
much below 65 degrees F. Also, some of the higher hills in the n the
Willamette Valley such as Mt Scott, the West Hills, Bald
Peak/Chehalem Mountain on the Yamhill/Washington County line and the
Salem Hills will likely remain within the thermal belt and remain
considerably warmer than nearby adjacent valley bottoms. In fact,
would not be surprised to see some of these sites also only bottom
out near 70F Saturday night despite the dry air in place. While this
detail has been incorporated into the forecast grids, agree with the
assessment of previous shifts that the localized areas in each of the
zones make it appropriate to maintain the current Heat Advisories in
place as opposed to upgrading the entire zones to Excessive Heat
Warnings.

Sunday still looks on track to be a transition day as a southerly
wind reversal works its way up the coast. It is already off the far
southern Oregon coast, a bit ahead of schedule, and is projected to
push onto the central Oregon coast by late Saturday afternoon or
evening and eventually onto the north Oregon coast either Saturday
night or early Sunday. As a result, slightly lowered temperatures
along the central Oregon coast and Coast Range where it`s looking
increasingly likely more likely the cooler marine air will exert its
influence. Enough marine air may also trickle into the Willamette
Valley that temperatures could end up a bit cooler than the current
forecast, especially near and south of Corvallis/Albany. Regardless,
there is high confidence thermal low pressure will shift east of the
Cascades Sunday night and result in the entire forecast area cooling
considerably by Monday.

Finally, a weak upper level impulse lifting northeastward into
northern California and Oregon late Sunday night and Monday will help
to destabilize the atmosphere is it brushes our southern CWA. At this
point, it appears there is a chance of thunderstorms grazing
primarily the Lane and Linn County Cascades. The current forecast
captures this well for now, but a subtle track in the synoptic
situation could very well either keep thunderstorm activity entire
clear of the forecast area or alternatively bring activity to a much
larger portion of the late Sunday night and Monday. Will need to
monitor the evolution of this feature as it approaches the region.
Cullen

.LONG TERM...Tuesday night through Saturday...Forecast models remain
in decent agreement for the start of the extended period. Lower-level
onshore flow will continue through at least the mid-week period as a
broad upper level trough moves through the Pacific Northwest. Expect
temperatures closer to seasonal norms Wednesday. However, maintained
a slight warming trend for the second half of next week along with a
dry forecast, as heights rise and the air mass warms a bit in
response to an upper level trough building over the region.
/mh Cullen

&&

.AVIATION...High pressure and offshore flow will bring
predominantly VFR conditions to most taf sites through 18z
Sunday. The main exception to this will be along the coast where
a southerly wind reversal will bring IFR conditions to KONP
sometime between 04-08z Sunday before transitioning to MVFR
conditions later on Sunday.

KPDX AND APPROACHES...High pressure and offshore flow will bring
VFR conditions through 18z Sunday. /Neuman


&&


.MARINE...High pressure over the northeast Pacific will continue
well into next week. In the immediate short term, a weak low
pressure will move northward across the waters over the next 36
hours. This will result in gusty north to northeast winds across
the outer waters this afternoon and evening before southerly
winds spread northward across all the waters tonight and Sunday.

A summer-like northerly wind pattern then looks to return late
Monday or Tuesday and continue through much of next week. This
should result in northerly winds peaking generally each afternoon
and evening across the waters...with the strongest winds
generally occurring across the waters off the central Oregon
coast. /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning from noon today to 9 PM PDT Sunday for
     Western Columbia River Gorge.

     Heat Advisory from noon today to 9 PM PDT Sunday for Cascade
     Foothills in Lane County-Central Columbia River Gorge-
     Central Willamette Valley-Greater Portland Metro Area-
     Lower Columbia-Northern Oregon Cascade Foothills.

     Heat Advisory from noon today to 9 PM PDT this evening for
     Central Coast Range of Western Oregon-Coast Range of
     Northwest Oregon-South Willamette Valley.

WA...Excessive Heat Warning from noon today to 9 PM PDT Sunday for
     Western Columbia River Gorge.

     Heat Advisory from noon today to 9 PM PDT Sunday for Central
     Columbia River Gorge-Greater Vancouver Area-I-5 Corridor
     in Cowlitz County-South Washington Cascade Foothills.

     Heat Advisory from noon today to 9 PM PDT this evening for
     Willapa Hills.

PZ...Small Craft Advisory for winds until 11 PM PDT this evening for
     Waters from Cape Shoalwater WA to Florence OR from 10 to
     60 nm.

&&


$$

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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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