Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 101201
Area Forecast Discussion
National Weather Service Portland Oregon
400 AM PST Sat Dec 10 2016
.SYNOPSIS...Winds are expected to turn west in the Columbia Gorge
today, finally bringing an end to the snow and freezing rain there.
Otherwise, a series of low pressure systems will maintain showery
weather into next week...with temperatures remaining near or below
normal. Snow levels will dip down to the Coast Range and Cascade
Foothills at times. Much colder weather will return beginning mid
week with the possibility of low elevation snow amounting to a
couple inches, but this remains very uncertain and no large snow
fall is currently expected.
.SHORT TERM...Tonight through Tuesday...THe upper high pressure east
of the Cascades is dramatically weakening at this hour with the 3 AM
Troutdale to The Dalles pressure gradient now a paltry 2.7mb
offshore. Have also noted a rising dew point trend in the Metro area
which further indicates the warmer air mass is growing closer.
Still, temperatures continue to hover around the freezing mark for
the bulk of the Metro and will likely do so for the next several
hours. Fortunately, we are seeing the back edge of the stratiform
precipitation with the back edge about to reach the Cascade crest
within the next hour or so. There will be scattered showers across
much of the region this morning with many areas possibly seeing
breaks in the clouds allowing some periods of sun to poke through
and help the warming effort. The showers should not amount to much
across the low lands nor in the mountains. As such, will expire and
cancel the full suite of winter warnings we have out. It will take
several hours for higher pressure to build west of the Crest and
turn the gradient and resulting winds west through the Gorge. Thus,
did leave a mention of intermittent freezing rain for the morning
period today, however amounts should be very insignificant and
especially with the present coating in place. Will issue an SPS
shortly to highlight concern for falling ice as temperatures warm.
Conditions will be especially hazardous in the Western Gorge where
ice accumulations were greatest.
Will see a series of shortwaves bringing fast moving fronts across
the region beginning late this afternoon and continuing through
Monday evening. The region will remain fairly close to the neutral
or slight on the warm side of the upper jet. They will arrive every
18-24 hours and appear to be fast moving enough such that snow
across the Cascades will likely remain close to or below the 12 hour
Snow Advisory amounts. Also, pass level temperatures will not stray
too far from freezing and would expect the snowfall to be rather wet
and heavy thus limiting accumulation rates. Travelers should still
expect periods of snow covered roads, however, as some of the
periods may bring a quick 3 to 5 inches over a relatively short
amount of time. Snow levels also remain low enough to limit the
amount of melt runoff into area rivers and minimize any threat for
flooding the next few days.
Monday night will bring a closed low diving well offshore which
allows brief upper ridging to appear over the area. Tuesday is
shaping up to be dry across the area. Am still maintaining some low
end PoPs from Salem southward as warm frontal rain will edge
northward from California. /JBonk
.LONG TERM...Monday night through Friday. No changes, Previous
discussion follows. There will be a chance of showers with valley
rain and mountain snow to start the period as an upper level trough
of low pressure slips southward into northern Calif. On Tues, a
fairly strong ridge of high pressure begins to move southward from
Canada into eastern Washington with an accompanying cold air mass.
This setup will bring offshore flow to the region for the middle and
latter part of the week. NWP models indicate there will be a fairly
dry period during the middle part of the week. A fairly strong east-
west pressure gradient sets up the latter part of the week brining
some strong easterly winds through the Gorge by weeks end. tw
.AVIATION...Slow change today, but at least there will be a
change. mild southwest flow aloft today will increase towards
evening as front approaches. VFR along the coast, with a few
showers and MVFR til 18Z, then increasing MVFR cigs 18z as rain
increases. Generally the same for the interior, just a few hours
delayed. But from 30 S of PDX to just n of KKLS, will see
widespread low MVFR and occasional IFR cigs this am. As day
progresses, this MVFR will improve a tad, but still high end MVFR.
Continued mountain obscurations through tonight.
KPDX AND APPROACHES...Persistent MVFR and occasional IFR this am.
Not a lot of change for CIGS today, though may see brief lifting
to VFR between 16z and 20Z. But after 20Z, cigs will lower back to
MVFR as rain spreads into the region. Light east winds continue
til 18Z, maintain temps in the lower 30s. But between 18z and 21Z,
will see shift to more southeasterly wind, and a bump in temps to
the middle 30s. Still think main jump in temps will occur later
this afternoon, as south winds 8 to 11 kt arrive. Rockey.
.MARINE...A front will bring increasing southwesterly winds with
widespread gusts of 25 to 30 kt this afternoon into this evening.
Front will push onshore early this evening, but gusty west to
southwest winds remain through Sunday. Generally, seas running 10
to 12 ft. Not a strong front, so Will not see big jump in seas with
the winds. Even so, seas will peak around 15 ft tonight.
Seas and winds will ease back Sunday night and Monday, but overall
not all that active. High pressure will build over inland PAC NW,
with another round of offshore winds after Tue. Rockey.
PZ...Small Craft Advisory for winds and hazardous seas through
Sunday on all coastal waters.
Small Craft Advisory for Rough Columbia River Bar conditions
Interact with us via social media:
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.