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FXUS66 KPQR 261634 RRA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
934 AM PDT Wed Apr 26 2017

.SYNOPSIS...A cold front is moving through the region this morning,
bringing rain and higher Cascade snow. Rain will transition to
showers later today. Showery weather will then continue through Thu.
Does appear will have a break for later Fri and Sat, with dry and
mild conditions. But, will see threat of rain return later Sat night
and Sun. With all these April showers, just imagine the size of those
coming Mayflowers. The weather appears to be trending toward warmer
and drier for next week.

&&

.SHORT TERM...(Today through Fri)...A strong Pacific jet stream of
160+ kt is aimed directly at the Pac NW today. IR satellite also
shows an extensive frontal boundary stretching from the Pac NW down
into the subtropics, with a fairly good late season moisture tap
feeding into the Pac NW. The frontal boundary has been pushing
through SW Washington and NW Oregon this morning, bringing a period
of steady precipitation to the region. Some areas in the Coast Range
and Cascade foothills have seen 24 hr rainfall totals in the 1 to 1.5
inch range. Totals along the coast and in the interior lowlands have
been closer to 0.5 inch. Precipitation has been falling as snow for
elevations roughly 4500 to 5000 ft and above. Area webcams show
accumulating snow at some of the higher passes this morning. Current
Winter Weather Advisory for snow above 4500 feet in the Cascades
continues, with 6 to 12 storm total snow likely. As usual, heaviest
snow will be on higher peaks/ridges, mainly above 5000 feet.

The steadier rain will be transitioning to showers later this morning
and this afternoon as the front pushes east of the region.
Showers will be decreasing in intensity from west to east across the
region this afternoon, but they will persist well into this evening
in the Cascades, thanks to favorable orographic flow.

Showers will be gradually decreasing tonight. But not expecting much
change in overall air mass on Thu. A few passing embedded
disturbances in the westerly flow on Thu will be enough to
destabilize air mass bit more, with showers increasing again later
Thu am into the afternoon. Snow levels remain between 3500 and 4500
feet, but with less precipitation amounts will result in only a few
inches of new snow. Showers will gradually decrease Thu night.

Now, after all the rain, we will need a break. Indeed, it appears
that break arrives on Fri. Still a minor threat of showers, but think
even that threat will be over the Cascades. Otherwise, will trend to
partly sunny skies with mild temperatures. Pyle/Rockey


.LONG TERM...Friday night through Tuesday...Showers continue to
further diminish later Friday through Saturday as an upper level
ridge over the eastern Pacific will further amplify in between low
pressure systems both upstream and downstream. Not quite confident
enough yet to bring sky cover to mostly sunny wording, but did trend
things that direction. Meanwhile, temperatures will also respond
accordingly with high temperatures in the afternoon warming into the
mid 60s - all the way to around seasonal normals, at least for one
day! However, this will be yet another only short-lived intermission
in the season of steady rain. A weakening frontal system will bring
increasing round of clouds, another chance of rain, and slightly
cooler temperatures. Forecast models do diverge a bit the first half
of next week, but as we transition to May there is some potential
for a bit of shift in the pattern. At this point, trended the
forecast dry for Monday and Tuesday, but did so somewhat cautiously
for two reasons - first, ensemble members continue to suggest a
somewhat large spread in possible solutions; second, we've seen this
sort of pattern in the models several times in recent weeks, where a
seeming trend toward dry conditions and a building ridge fails to
appear. That said, this would be consistent with the latest CPC 6-10
outlook of warmer and drier than average May 1-5 period. An abundance
of words to say the forecast was trended this direction but with
lower than typical confidence. Cullen
&&

.HYDROLOGY...The lower Columbia River will be running above bankfull
for the next several days. Primary areas of concern are the Columbia
near Vancouver and downstream past the Columbia near Longview to the
mouth. Contributions to the high flow are coming from high
astronomical tides in addition to increased runoff from the Snake
River and Willamette River basins. Lower reaches of tributaries
flowing into the Columbia River may also experience periods of
elevated water during the high tide cycles. Please continue to
monitor the forecasts for the next several days. /JBonk
&&

.AVIATION...Main focus of rain and showers will continue to drift
south this morning with showers developing north shortly then
closer to 18-20z for salem and southward. In the meantime, will
see periods where heavier ran bands and showers will drag cigs
down to MVFR and perhaps Vsbys close to IFR. Expect conditions
will generally improve this afternoon likely as prevailing VFR
after sunset and through most of the night. May get some low
MVFR stratus around or after 12z.

KPDX AND APPROACHES...VFR should prevail although may see
frequent cigs 030-040 through 00z today as showers stream across
the terminal area. Expect Minimal, if any, impacts to visual
approaches beginning with the afternoon boxer arrivals and
continuing through morning boxer arrivals. There is a 20% chance
of a 015 cig beginning around 14z. /JBonk

&&

.MARINE...Winds and seas are gradually becoming more benign this
morning. 06z WW3 data shows a 9 ft swell crossing the northern
waters late this afternoon and evening, however, am feeling the
associated GFS winds are slightly too strong. As such, have kept
the seas capped at 9 ft.

Broader high pressure builds over the NE Pac keeping a relative
lull in winds through Friday. Seas may next reach 10-11 ft
Thursday through early Friday as the southern end of a swell
train clips the northern waters from a surface low crossing the
Alaskan Panhandle. A deeper front may clip the waters Saturday
night for SCA level gusts. /JBonk

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 7 PM PDT this evening for
Cascades in Lane County-Northern Oregon Cascades.

WA...None.
PZ...Small Craft Advisory for Rough Columbia River Bar from 4 PM
this afternoon to 8 PM PDT this evening.

Small Craft Advisory for Rough Columbia River Bar from 3 AM to
8 AM PDT Thursday.

&&

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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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