Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 190916
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
215 AM PDT Thu Apr 19 2018

.SYNOPSIS...Dry and mild weather is expected today and Friday. A weak
frontal system will move across the region Friday night and Saturday
for light rain and Cascade snow. Dry and mild weather returns Sunday
and Monday.

&&

.SHORT TERM...Today through Sunday...Showers wrapping around an upper
low over Southern California are approaching the Oregon Cascades from
the east early this morning. Radar imagery shows these showers are
dissipating quickly once they reach the Cascades, and rainfall
measurements have been very unimpressive over the Cascades so have
decreased Pops.

An upper level ridge builds over the Pacific NW today and holds
through Friday for dry weather, mostly sunny skies, and warming
temperatures. Some high clouds will likely move over the region late
tonight and Friday as a frontal system approaches the coast.

A warm front will move well north of the area and have little impact
Friday morning, but the cold front will bring a chance of rain Friday
evening through Saturday morning with showers possibly lingering
across extreme SW Washington Saturday afternoon. The snow levels will
remain above the Cascade passes most of Friday then lower to around
3500 feet Saturday morning as the rain decreases and turns to
showers.  Rain and Cascade snow will be on the light side with the
highest 24 hour (Fri afternoon-Sat afternoon) totals around 0.20
inch along the north coast, north coastal mountains, and the south
Washington Cascades. The greatest chances for precipitation will be
along the coast late Friday night and over the Cascades Saturday
morning. The Willamette Valley, especially south of Salem may not
see much if any rain.

Showers will end Saturday night for a dry Sunday. Dry weather is
expected Sunday with surface high pressure over the area and
low-level offshore winds. However a shortwave upper trough moving
over the area will likely keep some clouds around, and limit heating.
Inland temperatures will be around around 5 degrees above seasonal
normal (mid 60s) this weekend. ~TJ

.LONG TERM...Sunday night through Wednesday...An upper ridge
amplifies on Monday continuing dry weather, and raising temperatures
to near or slightly above 70, possibly resulting in the warmest
weather of the year so far. A weakening front approaches Monday night
with increasing clouds Tuesday morning, and slightly cooler
temperatures Tuesday afternoon. An upper level trough may generate
showers over the OregonCascades Tuesday afternoon with snow levels
well above the Cascade passes. The forecast for Wednesday is less
certain as the models diverge on the position of an upper trough near
the region. THe GFS brings the trough over the area for cloudier,
cooler and showery weather whereas the ECMWF forecasts the trough
will stay further offshore and the weather in NW Oregon will be dry
and warm. Have leaned towards the ECMWF since model verification
shows that it generally out performs the GFS in long term
forecasting. ~TJ

&&

.AVIATION...Light ESE flow aloft around the upper level low that
continues to move into California. A few light showers may make
their way into the terrain of the Cascades, but otherwise
mid/high clouds gradually scattering will bring continued VFR
conditions for most locations early this morning. Expect
localized areas of patchy fog/low stratus 12Z-16Z in the Cowlitz
Valley and the southern half of the Willamette Valley as the most
favored locations. Otherwise, expect VFR under clearing skies
Thursday, though increasing mid/high clouds enter the region from
the northwest again after 06z Fri ahead of the next disturbance.

KPDX AND APPROACHES...VFR conditions expected to prevail through
the period with mid clouds continuing to scatter early this
morning. Some slight potential for some patchy fog near the
terminal between 12z and 16z.  Cullen

&&

.MARINE...High pressure over the waters today with light north
winds continuing. The next front approaches on Friday, likely
bringing another round of advisory strength winds Friday night
through early Saturday. Strong high pressure returns over the
Pacific over the weekend for a return of gusty north winds,
possibly reaching advisory criteria at times.

Seas will hold at 5 to 8 feet through early Friday, but build to
around 10 feet as the disturbance approaches Friday night/early
Saturday. Seas will subside a bit later in the weekend, but
expect periods to be relatively short given the contribution from
the gusty north winds, so conditions may remain steep at times
through early next week.    Cullen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
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 CWA or forecast area.


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