Funnel Cloud in Oregon, May 10, 2018

Area Forecast Discussion
National Weather Service Portland OR
953 AM PDT Thu May 10 2018

.SYNOPSIS...Cool and unsettled weather will continue today, with
scattered showers in the lowlands and more numerous showers in the
higher terrain. Showers will generally come to an end in the lowlands
this evening, while a few showers linger in the higher terrain
through Friday. High pressure will eventually take charge over the
Pac NW this weekend, with a warmup leading to well-above normal
temperatures by Mother's Day. Onshore flow returns early next week,
resulting in cooler but still above-normal temperatures.

&&

.SHORT TERM...Today through Sunday...Aside from some minor tweaks to
the forecast to end the showers a little earlier this evening in the
Willamette Valley, only minimal changes were made to the forecast
this morning. Models do show a vort lobe swinging south through
western WA/OR tonight, but this trajectory isn't the best to allow
showers to make it east of the Coast Range. Suspect a few showers
will linger in the higher terrain through Friday, but the inland
valleys should be mostly dry after this evening. High pressure ridge
and significant warmup still look on track for this weekend.  Weagle

Expect continued showers today as a pair of impulses embedded within
an upper trough will slide across the Pacific Northwest. Forecast
models are in reasonably good agreement through the short term
period. Despite the cool day featuring scattered showers across most
of the region, rainfall amounts will be rather modest and can't rule
out a few breaks in the clouds at times. On balance, probably not a
bad day at all as everyone can find something to enjoy. The weekend,
on the other hand, will be a bit more one-sided. If you prefer cool
and showery weather, this will not be your weekend. More on that in a
minute. Snow levels will lower a little - down to around 5,000 feet -
as the upper low moves over the region. While a little new new snow
may accumulate at the highest Cascade elevations, there should not be
any impacts at or near the Cascade passes.

By late Thursday and early Friday, the upper level trough migrates
east and south into the Great Basin, where models suggest it will
take up residence through much of the weekend. Meanwhile, expect a
warming and drying trend to develop closer to home as a strong
Pacific high builds into the far eastern Pacific and gradually sets
up over the Pacific Northwest. Our forecast area will initially be
situated in between these two aforementioned features in the weather
pattern. Expect some morning low clouds to give way to abundant
afternoon sunshine, with fewer clouds Saturday than Friday.
Temperatures on Friday may be kept a few degrees cooler in the far
southern Willamette Valley than points north if clouds are slower to
clear with the light northerly low-level flow in the valley. Saturday
will see temperatures well into the 60s along the coast and in the
upper 70s inland as offshore low-level flow may begin to develop. The
trend will further continue on Sunday as 850mb temperatures over the
region are modeled to reach 14-17 degrees C, well above the 90th
percentile values of observed 850 mb temperatures for this time (as
measured at the KSLE upper air site). This translates into afternoon
temperatures well into the 80s across the interior valleys on
Mother's Day. While these high temperatures would be some 15-20
degrees above average for the holiday, they will still remain well
short of record warmest Mother's Day holiday (records for the holiday
are generally 90-95 degrees F in the valley).	Cullen

.LONG TERM...Sunday night through Wednesday...Forecast models remain
in decent agreement for the very beginning of next week, but become
more diverse in their solutions by midweek. There remains some notion
of a wind reversal developing along the coast late Sunday night,
which will bring a surge of clouds and cooler marine air from south
to north along the coastal areas. Expect this push of marine air to
perhaps enter the southern Willamette Valley around Eugene by early
Monday; however, the more significant marine push will hold off until
Monday night when the marine layer deepens. With onshore flow again
increasing over the region, temperatures will return to much closer
to seasonal norms for Tuesday and Wednesday. The upper low over the
Great Basin will gradually weaken, but an approaching upper low over
the Pacific is expected to cut off and remain off the California
coast by Tuesday evening. While a wide range of possible solutions
remain for the midweek period, have increased cloud cover and
introduced PoPs for Wednesday across the southern half of the
forecast area as some showers associated with this upper low may
rotate into the region. While confidence in the details remains lower
than normal beyond Tuesday due to uncertainty in the position of the
upper low, enough evidence in the ensemble guidance to warrant at
least a slight chance mention in the forecast for Wednesday.  Cullen

&&

.AVIATION...VFR conditions are already giving way to MVFR cigs
early this morning as a secondary front moves into the area,
producing areas of light rain. The rain or showers are expected
to continue through much of today, with cigs slow to rise,
possibly reaching VFR later today. Onshore flow and the
associated upper level system will keep clouds across the area
with a few showers tonight, and cigs will likely lower back to
MVFR overnight tonight and on Fri morning.

KPDX AND APPROACHES...VFR cigs will probably lower to MVFR as
rain develops before sunrise this morning and continues off and
on much of today, breaking up to showers later today and tonight.
Cigs may lift to VFR later today and this evening before dropping
back to MVFR later tonight and Fri morning. pt

&&

.MARINE...SW winds will shift to NW fairly early this morning
behind a secondary cold front moving through, and as higher
pressure builds into the coastal waters through the day today
behind the front. Winds will increase tonight and Friday and
will likely exceed Small Craft Advisory thresholds, weakening
Friday night and Saturday. Winds will stay out of the N or NW
until a southerly wind reversal likely develops and spreads
northward along the the coast Sunday night and Monday. Winds
turn NW again later next week.

Seas are 4-5 ft this morning but are forecast to rise to 10-11 ft
tonight by our wave models due to the increasing NW winds. Seas
are expected to slowly drop below 10 ft later Friday and Friday
night. Seas then stay below 10 ft well into next week. pt

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds from 5 PM this afternoon to 11
     PM PDT Friday for Coastal Waters from Cape Shoalwater WA
     to Cascade Head OR out 60 NM.

     Small Craft Advisory for hazardous seas from 6 PM this evening
     to 3 PM PDT Friday for Coastal Waters from Cape Shoalwater
     WA to Cascade Head OR out 60 NM.

     Small Craft Advisory for winds from 8 PM this evening to 5 AM
     PDT Saturday for Coastal Waters from Cascade Head OR to
     Florence OR out 60 NM.

     Small Craft Advisory for hazardous seas from 8 PM this evening
     to 3 PM PDT Friday for Coastal Waters from Cascade Head OR
     to Florence OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar from 1 AM to
     4 AM PDT Friday.

     Small Craft Advisory for Rough Columbia River Bar from 11 AM to
     4 PM PDT Friday.

&&

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland

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 CWA or forecast area.