Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 231208
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
302 AM PST Thu Nov 23 2017

.SYNOPSIS...A series of fronts will continue periods of wet weather
into next week. Snow levels will remain above the Cascade passes
through Thursday morning. Snow levels will then lower to near the
Cascade passes Thursday night, but the precipitation will be light.
There is a better chance for snow to impact the passes Sunday and
Monday.

&&

.SHORT TERM...Today through Saturday...Cold front falling apart over
the interior lowlands or Cascade foothills and rain has decreased.
Another front strengthens offshore this morning then moves through in
the afternoon, sagging south and east this evening. Moderate rain
will impact the north coastal mountain and Cascade zones today. This
will bring another rise to rivers in those basins, but not to
significant levels.  The cold front will stall out to the south of
our CWA but then push north again as a warm front. It will likely
generate showers along the coast and SW Washington Friday morning,
but precipitable water values lower considerably (~0.5 inch) and the
rain totals should be fairly light (<0.15 in). Areas away from the
coast south of Salem will be mostly dry late Friday morning into
early Saturday morning.

The drainage basin for Grays River will see enough rain again today
to extend the time it remains above flood stage into some time
tonight.

Snow levels will be slow to drop.  It will be tonight before they
lower to any impactful level for possible travel concerns over the
Cascade passes. Still, this will be after the heavier precipitation
moves well east of the area. May get a few inches of snow to
accumulate at the 4500 foot plus pass elevations
by early Friday, and that may be generous at best.

Models are even slower with the approach of a low from the SW Friday
night and Saturday and have trended forecast that way. There may be a
dry period for much of the CWA later friday night and Saturday
morning. But looks like rain will arrive Saturday afternoon as the
low swings a warm front south-to-north across the CWA. Snow levels
will rise back to above 8000 feet late Saturday morning,
and do not have any winter weather concerns. /mh

.LONG TERM...Saturday night through Wednesday...No changes,
previous discussion follows: Snow levels will lower down to the
Cascade passes late Saturday night or early Sunday morning behind a
front. The front should move east of the Cascades late Sunday
morning, but will be followed by another front Sunday night into
Monday. A cold upper trough will help keep snow levels down to near
or just below the Cascade passes through Monday evening. The models
vary on when the Upper trough will move east, but agree that an
upper ridge will replace the upper trough by Tuesday.
This will favor increasing snow levels and decreasing rain chances
Tuesday and Wednesday. ~TJ

&&

.AVIATION...Moist southwest flow aloft, with plenty of clouds.
Front appears to be pushing slowly across the I5 corridor towards
the Cascades. Widespread IFR and low MVFR along the coast will
persist this am, then slowly improve to MVFR by midday. Mix of
VFR and MVFR inland, though think will see more MVFR between 12Z
and 20Z as air mass remains moist thanks to onshore flow behind
the front. Will generally improve to more VFR between 20Z and
22Z for inland areas. Expect higher terrain and passes over the
Cascades to be obscured in clouds for good part of the day.

KPDX AND APPROACHES...Mix of VFR and MVFR this am, with more MVFR
than VFR as air mass remains moist with occasional light rain and
drizzle this am. Will slowly improve to VFR after 21Z, with CIGS
lifting to around 5000 ft. But, will see increasing MVFR after
04Z as air mass cools and lower clouds develop.        Rockey.

&&

.MARINE...Cold front now well inland, and winds have eased back
under 20 kt. Still have rather broad area of low pres offshore.
So, will maintain south to southwesterly winds on the waters
through Fri, though winds generally 10 to 20 kt, with gusts 25 kt
at times through tonight. Seas holding at 10 to 12 ft today, but
will slowly subside tonight into Fri am. So, will cover seas and
winds with Small Craft Advisory through tonight.

Break in the weather for Fri into Sat, then will a couple of
strong fronts will push over the region later Sat and again late
Sun. System on Sat will see deep low pres moving north just inside
of 130W. This should be close to support solid southerly gales on
the waters later Sat and Sat night, with seas building to 15 to 20
ft. Another front will push across region later Sun and Sun night.

Next week looks to be much more tranquil weather as high pres
builds over the region. If trends continue, could see northerly
winds 10 to 15 kt for good part of next week. But seas will vary,
due to various swell fetches arriving next week.      Rockey.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.

WA...None.

PZ...Small Craft Advisory for winds and hazardous seas on all
coastal waters today and tonight.
     Small Craft Advisory for Rough Columbia River Bar conditions
until 10 am today, and again 5 to 10 pm today.

&&

$$

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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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