High Surf in Washington, November 15, 2020

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1002 AM PST Sun Nov 15 2020

Updated Aviation and Marine Sections

.SYNOPSIS...Classic, unsettled November weather will prevail across
the Pacific Northwest for much of the upcoming week. Expect
seasonably cool temperatures and scattered showers today. The cold
front which moved south of the forecast area late Saturday will lift
back northward as a warm front, bringing another round of rain and
mountain snow later tonight and Monday. Monday afternoon and evening
will be mild and mainly dry, potentially with a few breaks in the
clouds. Another strong front will push into the region for wet and
breezy weather Tuesday, followed by another round of cool and
unsettled weather through Thursday. Drier weather looks possible by
next weekend.

&&

.SHORT TERM...Today through Tuesday...As of 3 AM, the latest NOAA
satellite and radar imagery shows our frontal zone sagging south of
the forecast area, taking the steadiest precipitation with it. This
front produced another decent round of rain and wind, with several
inches of snow above the Cascade passes. Rainfall totals over the
past 24 hours generally ranged from around 1 inch in the lowlands up
to 3 inches for some of the wetter spots in the Oregon Coast Range
and Cascades. The associated runoff continues to fill our rivers,
most of which again saw modest rises from this system. Fortunately
the heaviest rain remained south of the Willapa Hills, sparing the
Grays River from any flooding.

Snow showers continue in the high Cascades with mixed rain/wet snow
at pass level. We allowed the Winter Weather Advisory to expire for
the North Oregon Cascades, as we're only expecting a couple more
inches of snow, and mostly above 4500-5000' elevation. Meanwhile,
low-level cool air remains locked in the Hood River Valley, where
there are likely some icy spots this morning. West winds should break
through shortly, allowing temperatures to rise well above freezing
today.

Otherwise, today will be a fairly typical November "break" day
between weather systems. Enough instability exists below 700 mb to
support scattered showers, but there will probably be some shadowing
to the lee of the Coastal Ranges and Cascades. Overall, today should
be more dry than wet for most of the forecast area. Despite
yesterday's front technically being a cold front, it should be a few
degrees warmer today for most of the forecast area, with seasonable
highs in the lower to mid 50s for the lowlands. A few patches of
shallow morning fog will dissipate fairly quickly after sunrise.

Models now showing the front lifting back north as a warm front
Sunday night, with rain spreading northward overnight. Not expecting
heavy rain with this system, but mostly 0.25 to 0.50 inch of rain for
tonight through Monday morning. This warm front will lift north
quickly Monday morning, with rain well north of the Columbia River by
mid to late afternoon. Still decent amount of clouds across region.
But, with no rain and some breaks in the cloud cover, seems
reasonable to get afternoon temperatures into the upper 50s to lower
60s, especially for areas south of Salem. Dry weather on tap for
Monday night. But, with high pressure east of the Cascades, and
deepening low pressure well offshore, will see increasing easterly
winds.

Next system arriving Tuesday, with rain spreading inland early in the
day. But, some uncertainty with this system. At moment, models
trending with rather strong low offshore that will lift north-
northeast towards Vancouver Island during the day. With that in
mind, will likely stay on lighter precipitation side for most of the
day, along with somewhat breezy east to southeasterly winds. But, if
low tracks more eastward, then we could easily get into more rain and
better potential for breezy south winds. For now, will go ahead with
a High Wind Watch for this system Tuesday for the South Washington
and North Oregon Coasts. Oregon's Central Coast may eventually need a
watch if some of the more southern and eastern low tracks within the
ensemble suite pan out. This system has the potential to produce very
strong winds along the coast, or not, and much will depend on the
track. Historically, models tend to be a bit too far south and east
with rapidly intensifying lows off our coast, but not always.

Either way, looks to be another wet day for the region. Another
concern will be the potential for tidal overflow along the south
Washington coast on Tuesday afternoon. Given uncertainty of wind
speeds and seas, will have to watch this as draw closer.
Weagle/Rocket

.LONG TERM...No Changes. Previous discussion follows...Tuesday night
through Friday...Cluster analysis shows a high probability that the
region will continue to be on the leading edge of a deep upper level
trough Tuesday night. The deep upper level low will shift north and
dissipate by Wednesday night. The surface low will continue to
strengthen Tuesday as it moves northeast towards Haida Gwaii. By
Tuesday evening surface winds will likely shift onshore bringing
stratiform rain within the warm front across the region. Gusty
southerly winds are expected Tuesday night as gradients tighten
within the warm front. NBM shows a 40% chance that KPDX will see wind
gusts up to 35 kt, wind gusts will likely stay between 20 to
25 kt. These stronger gusts are possible if this low continues to
strengthen like the models are depicting at this time.

The 12Z GFS and NAM both show a weak shortwave ahead of the cold
front which will likely support another rise in QPF Wednesday
afternoon. Cold front will likely push onshore Wednesday night
bringing showers across the area into Friday. Potential for a
transitional period Friday as a transient upper level ridge moves
across the Pacific NW. Weak surface ridging is likely to build
Friday night which could bring a brief pause in the rain. But, as
this is so far out confidence is low.		  /BPhillips

&&

.AVIATION...Generally VFR over the area as of 18Z. Westerly
orographic flow into the Coast Range and Cascades will maintain
lower conditions at times through the day. The coast and interior
lowlands will remain primarily VFR through at least 06Z Mon.
However, as is typical in a post-frontal air mass, there will be
brief periods of MVFR in showers. A warm front over southwest
Oregon early this evening shift north tonight. Expect MVFR
conditions to develop south of a KS12-KONP line after 06Z Mon,
with IFR likely along the coast south of KONP. Conditions improve
to VFR over the south part of the forecast area late Mon morning.
MVFR conditions reach the northwest Oregon late tonight.

For detailed regional Pac NW weather information, go online to:
http://weather.gov/zse

KPDX AND APPROACHES...VFR through the period. There will be brief
periods of cigs around FL040 this afternoon through early
evening, with a 20-30% chance of MVFR cigs associated with
showers. Cigs 060-080 late evening into early Mon morning, then
lowering after about 10Z as a warm front reaches the area. East
wind 15g25kt to develop at the west end of the Gorge Mon morning.
Weishaar

&&

.MARINE...Wind speeds continue to subside this morning, generally
10-15 kt with gusts to 20 kt. Wind backs to southwest this
afternoon and then southeast to south tonight. Models in decent
agreement indicating a return to gale force wind over PZZ255 and
PZZ275 mid to late Mon morning with a warm-frontal passage. East
wind persists over the north zones into early Mon afternoon,
followed by gale force south wind. Will maintain the current gale
watch, but feel these conditions will be most prevalent over the
outer waters. There is still plenty of model disparity regarding
the strength and location of the surface low Tue. Specifically,
the 06Z ECMWF ensembles show quite a bit of variability with
surface low placement. In any event, latest models continue to
suggest storm force wind Tue. Exact timing and magnitude remain
in doubt due to the model variability.

The ECMWF and ENP wave guidance show seas 20-22 ft over the
northern waters this afternoon, with the highest waves along the
south Washington coast. Buoy 46005 registered 30-ft wave heights
at 02Z. This decays to around 22 ft at buoy 46029 early this
afternoon. See no reason to adjust the forecast with no new
information. Not having buoy 46089 makes it difficult to time the
peak waves into the north Oregon coast. Seas ease into the mid-
teens by 08Z Mon and to the low teens Mon morning. The ENP model
shows 20-25 ft seas along the coastline Tue morning. The ECMWF
model is 2-3 ft lower. Both models show this to be more of a
southwest swell with relatively short periods.

Expect somewhat more benign conditions during the second half of
next week as higher pressure likely returns to the northeast
Pacific. This looks like seas will drop below 10 ft for a multi-
day stretch beginning Thursday. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...High Surf Advisory until 7 PM PST this evening for Central
     Oregon Coast-North Oregon Coast.

     High Wind Watch from Tuesday morning through Tuesday afternoon
     for North Oregon Coast.

WA...High Surf Advisory until 7 PM PST this evening for South
     Washington Coast.

     High Wind Watch from Tuesday morning through Tuesday afternoon
     for South Washington Coast.

PZ...Gale Watch from Monday morning through late Monday night for
     coastal waters from Cape Shoalwater WA to Florence OR out
     60 NM.

     Storm Watch from late Monday night through Tuesday afternoon
     for coastal waters from Cape Shoalwater WA to Florence OR
     out 60 NM.

     Small Craft Advisory until 10 AM PST Monday for coastal waters
     from Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory until 10 PM PST Monday for Columbia River
     Bar.

&&

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