High Surf in Oregon, March 5, 2021

Area Forecast Discussion
National Weather Service Portland OR
347 AM PST Fri Mar 5 2021

.SYNOPSIS...A rather complex system continues to slowly move inland
today as the overall system weakens. Another front arrives Sunday,
also weakening as it comes onshore. Generally speaking, the coast
will receive the bulk of precipitation while the Cascades receives
far less. Low pressure slowly slides south while centered well
offshore to bring some form of rain and snow for much of next week.

&&

.SHORT TERM...Today through Sunday Night...The upper front, which
has stalled a bit further west than was expected 24 hours ago, is
starting to move back onshore this morning. The further west
position has resulted in rather meager rain amounts as compared to
what was expected by previous shifts. As of this forecast package
QPF storm totals are running about half of the -24 hr forecast.
Given this, any flooding concerns there were for the Grays and
Nehalem rivers are long gone.

The leading edge of rain will cross over the Willamette Valley close
to daybreak which will help break up the patchy fog which has
developed under the clearer to start skies from the last several
hours. Expect rain to be more on than off today until the back edge
of the front crosses this afternoon and for the Cascades, this
evening. Will be curious to see how much shadowing influence comes
into play from the southerly flow intersecting the Siskiyous and the
Umpqua divide to our south. Already diminished QPF amounts may still
be overdone. Will get a few inches of snow for the Cascades with the
Mt St Helens region likely picking up several inches under the more
favorable southerly flow, but still staying below advisory criteria.
Additionally with this front, will get some breezy to borderline
windy conditions at the coast this morning as smaller scale impulses
move north along the front. Gusts 35-45 are most likely for the more
exposed beached and headlands. Cannot rule out the occasional gust
around 50 mph this morning.

Also along the beaches, incoming westerly and longer period swells
will increase the chance of sneaker waves today. Additionally, very
small tsunami waves have begun to arrive at the coast early this
morning. Although they will have some influence, the primary sneaker
wave threat will be from distant storms and not necessarily from the
earthquakes off the northern New Zealand.

Temperatures over the next few days will stay a few degrees below
normal. Saturday will remain showery under a modestly unstable air
mass. May get some small hail embedded in the showers. Showers taper
off near sunset Saturday evening and then another front will cross
the region late Saturday night and early Sunday morning. This front
will also likely end up weaker and splitting to result in what may
be perceived more as showers in the morning. The front, or what's
left of it, does move east rather quickly leaving Sunday afternoon
more convective. Sunday's showers may have a bit more strength to
them as the colder air mass from the broader upper low does move
overhead. Thunderstorm chances are low and below a mentionable 15%,
however, they are not completely zero. Should surface Ts run a
couple degrees higher than expected, then a sub 15% thunder threat
might bump up closer to 25-35%. /JBonk

.LONG TERM...Monday through Thursday...Another large upper low
will work southeastward from the Bering Sea over the weekend to take
up residence between 130 and 140 W off the PacNW coast. This system
will then further drop south and then southeast during the several
day period of the long-term forecast. As it does so, there will be
opportunities for short-waves to rotate around the base of the upper
low and bring rain chances every day through Tuesday. Wednesday and
Thursday have the best chances for staying dry albeit with
temperatures remaining somewhat below normal. As of now, do not
expect any significant snowfall for the Cascades, but at least what
does fall will likely remain snow, especially across the passes and
higher. /JBonk

&&

.AVIATION...12Z TAFs: At 11Z Friday, a strong cold front was
located over the coastal waters. Ahead of this front, broken mid
to high clouds with cigs in the 5000-8000 ft range are occurring
along the coast and into the Coast Range and Willapa Hills.
Further inland over the interior valleys, mostly clear skies have
helped areas of fog develop. Fog is dense in some spots early
this morning, especially over the northern Willamette Valley.
In addition, light rain has already begun along the coast and
will keep pushing inland this morning as the aforementioned
front finally moves across southwest WA and northwest OR. As it
does so, cigs will most likely lower to MVFR along and near the
coast between 14-15Z, and over the Willamette Valley between
16-19Z.

This front will also bring a somewhat brief period of gusty
southerly winds as it passes through this morning, especially
along the coast where gusts around 35-40 kt are expected between
12-15Z. Further inland, gusts around 20-25 kt appear likely
between 15-18Z. This is also when any lingering fog will mix
out, which should mix out very quickly thanks to the sudden onset
of gusty winds. Lastly, expect a period of low-level wind shear
across much of the forecast area this morning as southwest winds
at 2000 ft increase to around 50 kt.

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

KPDX AND APPROACHES...Patchy fog is possible at or nearby the
KPDX terminal between 12-15Z this morning, which will be handled
with VCFG in the beginning of the 12Z TAF period. Aside from the
nearby fog, expect VFR cigs to continue early this morning with
cigs between 5000-8000 ft. Cigs should eventually lower to MVFR
around 17Z as a cold front moves in with light rain. This front
will also bring low-level wind shear concerns between 14-18Z as
southwest winds at 2000 ft increase to around 50 kt. At the
surface, southerly winds with gusts around 20-25 kt are likely
near and behind the front between 16-19Z. Expect VFR flight
conditions to return in the late afternoon or early evening. -TK

&&

.MARINE...Buoy observations early Friday morning showed
significant wave heights around 20 ft across the outer waters,
and around 15-16 ft over the inner waters. Combined seas were
resulting from a combination of a fresh southerly swell and a
long period westerly swell. In addition, a strong cold front was
located over the inner waters, which should begin to push inland
just before sunrise. This front has brought gusty southerly
winds, with buoy observations continuing to show gusts in the
40-45 kt range. By late morning, winds should fall into the 25-34
kt range while combined seas begin to decline into the mid teens.
Therefore, it is likely that the Gale Warning will be replaced by
a Small Craft Advisory by late this morning. That said, a few
gusts to 35 kt cannot be ruled out late this afternoon to the
north of Tillamook Head beyond 30 nautical miles.

Expect winds to decrease significantly tonight, falling below 20
kt by late tonight. Despite the weakening winds, seas look to
stay elevated in the low to mid teens. It is not until Saturday
afternoon that seas should fall to around 10-11 ft. Southerly
winds increase again Saturday evening as the next frontal system
moves over the waters. At this time, a brief period of gusts
between 30-35 kt appear likely with the front.

Westerly swell begins to increase again on Sunday, with guidance
suggesting a peak around 18-21 ft by the late afternoon. With a
dominant period around 16-17 seconds, this will bring a high
sneaker wave threat to local beaches and will also bring the
potential for high surf. Expect both seas and winds to improve
significantly early next week. -TK

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Gale Warning until 9 AM PST this morning for coastal waters
     from Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory until 1 PM PST Saturday for Columbia River
     Bar.

&&

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