Small Craft Advisory 35, NWS Portland, OR

Area Forecast Discussion...UPDATE
National Weather Service Portland OR
903 PM PST Tue Mar 2 2021

Updated aviation and marine discussions

.SYNOPSIS...Mild and mainly dry Spring-like weather will hold through
early Thursday before a series of storm system bringing a return to
valley rain and mountain snow late in the week into the weekend.

&&

.SHORT TERM...Tonight through Friday...What remains of a stalled,
dying front continues to spread out across the northwestern part of
the CWA tonight. Weak surface ridging develops through Wednesday,
which will maintain dry conditions across the CWA along with a
warming trend which will result in high temperatures for inland
valley locations reaching the upper 50s to low 60s, coastal locations
and the Cascades warming into the upper 40s to mid 50s through early
Thursday.

Over the next few days a trough coming from the Aleutian Islands
will slowly progress into the eastern Pacific Ocean and by Thursday
afternoon will start to impact our area. The key features through the
latter part of this week will be the trough and a weak to low end
moderate atmospheric river. The trough and associated front will turn
this atmospheric river flow south to north, rather than the typical
west to east flow. Guidance does have total QPF values of 2 to 3
inches by Friday night for areas along the Coast Range with total QPF
values lowering further east with inland valley locations picking up
between 0.50 and 0.25 inches and the Cascades seeing less than 0.25
inches by Friday night. Given the south to north orientation, the
likelihood of hydrological impacts remain low at this time. However,
areas like the Grays and Nehalem rivers will be closely monitored
given that some areas still have a snow lingering in the upper
elevations. /42

.LONG TERM...Friday night through Monday...Friday night models have
the upper level trough axis over or past the Cascades. The cooler air
behind the front will drop snow levels but the bulk of the
precipitation looks to be done by that time. Saturday shortwave
ridging looks to take place which will lower precipitation chances
but given that there is some uncertainty between the operational
models have chosen to not deviate much from the NBM which keeps a
chance of precipitation across the CWA. As Sunday approaches a colder
low looks to dive down from the Gulf of Alaska towards the Pacific
Northwest, which will bring cooler temperatures, lowering snow levels
with valley rain and mountain snow through Monday. /42

&&

.AVIATION...High pressure will continue over the region tonight
into tomorrow, bringing calm to light and variable winds and
mostly clear skies. This setup will be ideal for areas of fog and
low stratus to develop later tonight, especially after 11Z
Wednesday. It appears fog will be a little more widespread than
last night, with dense fog possible at times. All TAF sites have
the potential for fog tonight into Wednesday morning, but
KHIO/KUAO/KEUG appear to have the best chance. Any fog or low
clouds that develop overnight should last well into Wednesday
morning, and perhaps into early afternoon over the southern
Willamette Valley. Skies should eventually become mostly clear
again once fog and low stratus scatters out between 17-21Z
Wednesday.

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

KPDX AND APPROACHES...Nearly calm winds and mostly clear skies
will continue through much of tonight, before chances for fog
and/or low stratus increase after 11z Wednesday. Dense fog is
not expected at the terminal at this time, but cigs around 800
ft are becoming more likely beginning around 12Z Wednesday. -TK

&&

.MARINE...Buoy observations late Tuesday evening showed seas
still hovering around 12-13 ft, which is several feet higher than
what wave guidance has been suggesting. This is due to a
northwest swell that is taking longer than expected to fall below
10 ft. Therefore, the Small Craft Advisory has been extended for
all waters through tonight before dropping off after sunrise when
seas should finally fall below 10 ft. A Small Craft Advisory has
also been extended through 10 am PST Wednesday for the main
channel of the Columbia River Bar, due to seas running higher
than expected and Wednesday's morning strong ebb likely resulting
in seas to 10 ft with breakers possible.

Conditions deteriorate Thursday as a strong but slow moving cold
front approaches. Moderate to high potential for strong
southerly gales, along with seas building back to 17 to 22 ft. A
Gale Watch has been issued for all waters beginning Thursday
morning and continuing through mid Friday morning. Winds and
seas will drop back a bit on Friday afternoon, but unsettled
weather will continue into the coming weekend. -TK/Weagle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Gale Watch from Thursday morning through Friday morning for
     coastal waters from Cape Shoalwater WA to Florence OR from
     10 to 60 NM.

     Small Craft Advisory until 7 AM PST Wednesday for coastal
     waters from Cape Shoalwater WA to Florence OR out 60 NM.

     Gale Watch from Thursday morning through Friday morning for
     coastal waters from Cape Shoalwater WA to Florence OR out
     10 NM.

     Small Craft Advisory until 10 AM PST Wednesday for Columbia
     River Bar.

&&

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