Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 232225
Area Forecast Discussion
National Weather Service Portland OR
325 PM PDT Thu Mar 23 2017
.SYNOPSIS...An occluding Pacific frontal system will spread rain
across southwest Washington and northwest Oregon this afternoon into
tonight, with showers and a few thunderstorms lingering into Friday.
High pressure will cause showers to taper off late Saturday, but the
next frontal system will likely bring more rain Sunday followed by
showers Monday. Occasionally wet weather is expected to linger
through the middle of next week.
.SHORT TERM...Tonight through Sunday...Visible satellite imagery
continues to show mid and high clouds filtering into southwest
Washington and northwest Oregon this afternoon ahead of an
approaching frontal system. Doppler radar is also starting to show
some light returns this afternoon, but based on recent surface
observations suspect this is mainly falling as virga at the moment.
Otherwise, the forecast remains on track for this afternoon and
tonight with rain arriving at the coast in the next several hours and
pushing inland this evening. Rain with this front could be heavy at
times, but models continue to keep the highest QPF over southern
Oregon. In general, expect around 1 to 1.5 inches of rain along the
coast and in the coast range and portions of the Cascades through
Friday. The interior could see around 0.5 to 1 inch. Snow levels look
to remain above the passes tonight and Friday, with the high Cascades
likely getting another 4 to 6 inches of new snow.
Rain will turn to showers along the coast by Friday morning and
inland by the afternoon as the cool upper level trough starts to move
onshore. Models continue to show around 200 to 500 J/kg of CAPE over
the forecast area tomorrow afternoon, with 0 to 3 km bulk shear
around 25 kt. If we are able to get any sunbreaks tomorrow afternoon
we could see a few thunderstorms develop across the region. However,
this is a big if. Despite this have decided to keep the mention of
thunder in the forecast, but will hold off adding the mention of
gusty winds or small hail.
Showers look to continue into early Saturday, but as high pressure
builds into the Pacific Northwest late Saturday these showers will
likely come to an end for a brief period of dry weather Saturday
night. The next frontal system looks to impact the forecast area on
Sunday bringing the return of cool and wet weather. /64
.LONG TERM...Sunday night through Thursday...12z global models are
in general agreement with evolution of the long wave pattern,
however, details are far too sketchy to pin down specific dry
periods. This is somewhat of a shift from earlier runs where the
early part of next week showed signs of a brief dry period. COld
front Sunday night will push east through early Monday. Plenty of
orographic showers will follow through Monday evening. There, the
GFS and ECMWF start to show differences among the operational runs.
Have thereafter decided to stick fairly close to a blend of the
ensemble means as the ECMWF is slightly more progressive with the
westerly flow while the GFS is continuing more of the amplified
pattern it`s shown the last few days. The 12z runs do come back
together on Wednesday/Wednesday night with a trough sweeping east
across the region. For now, that looks like the wettest day although
given the run to run inconsistency, have kept lower end likely pops
for now. Regardless of the details, overall conditions will close to
seasonal temperature norms which keeps snow levels bouncing between
4000 and 6000 feet. /JBonk
.AVIATION...VFR conditions this afternoon are likely to give
way to MVFR conditions along the coast between 22z and 02z late today
as rain associated with a cold front increases. There is a chance
for seeing short-lived periods of IFR visibilities during periods of
heavier rain mainly between 02z and 06z. Once the front moves inland
expect conditions to improve back to mainly VFR conditions with
showers after 11z. Inland expect mainly VFR conditions to prevail
tonight into Fri, but from 04z through 13z expect at least a
chance for temporary MVFR conditions associated with the front.
KPDX AND APPROACHES...VFR conditions remain most likely tonight
throughout tonight, but there is a chance for seeing MVFR conditions
in rain between 04z and 13z as a cold front slowly moves through.
After 13z VFR conditions are expected to prevail.
.MARINE...Cold front will move east across the coastal waters early
this evening, likely reaching the coast between 6 and 8 pm. By early
afternoon winds over the outer waters were approaching gale force,
and are expected to become solidly gale until after the front moves
through over the outer waters. Inner waters will be a little slower
coming up to gales this evening due to a little bit of an offshore
component to the wind. Will see winds turn more to the west and
decrease behind the front later tonight into Fri, but with gusts
still on the order of 20 to 25 kt through Fri. Seas will respond to
the local winds tonight meaning they will be steep, and are expected
to rise to around 15 ft. By late tonight though as winds subside so
too will seas, down to around 10 ft Fri. A ridge of high pres moves
slowly east across the coastal waters Fri night through Sat night
for quieter weather.
Sun another cold front approaches from the west, increasing winds
again. Winds with this system expected to gust as high as 30 to 35
kt late Sun.
PZ...Gale Warning until 1 AM PDT Friday for Waters from Cape
Shoalwater WA to Florence OR from 10 to 60 nm.
Gale Warning until 3 AM PDT Friday for Coastal Waters from Cape
Shoalwater WA to Florence OR out 10 nm.
Small Craft Advisory for Rough Columbia River Bar from 9 PM
this evening to 5 AM PDT Friday.
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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.