756
FXUS66 KPQR 212302
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
302 PM PST Thu Nov 21 2024

.SYNOPSIS...A few showers today, then rain returns tonight into
Friday along with another round of windy conditions Friday. Showery
weather followers over the weekend into next week.

&&

.DISCUSSION...Today through Wednesday...A low continues to drift
northeast-ward towards the PNW, and weak showers continue to drift
through the area for the rest of today. This low continues to deepen
as it moves closer. This system supported by a 125-130kt jet will
rapidly deepen tonight as it swings to just inside 130W of the WA
coast late Friday afternoon. Pressure drop with this storm will not
be as impressive as the recent meteorological bomb with about 18 mb
drop in 24 hours. This system will bring another round of strong
winds over the coastal waters and at the coast. Winds are currently
generally easterly, with some gusts up to 20-25mph through the
Columbia River Gorge; these will shift southerly by 8pm Thu as the
system approaches, and gusts will increase around then. Looking at
the latest high-resolution HREF guidance, between this evening and
Friday morning, southerly winds at the coast could potentially gust
up to 60 mph (60-80% confidence) at the beaches and headlands, and up
to 40-45 mph in the central Willamette Valley (80% confidence). As a
result, a High Wind Warning has been issued at the coast, while a
Wind Advisory has been issued for the central Willamette Valley.

Rain will spread south to north tonight into Friday morning, with IVT
plume peaking around 500 kg/ms. Duration will be relatively short, as
the main stream of moisture only briefly crosses into the area as the
warm front sweeps north with the low. Inland, 24h total QPF looks to
be around 0.5-1.0" from 4 PM Thursday through 4 PM Friday. Over the
mountains and coast, QPF looks closer to 1.25-2" during this time.
Hydro impacts continue to look minimal, with HEFS guidance showing
less than 5% chance of minor flooding for Coast Range rivers.

Snow levels continue to rise above Cascades pass level ahead of the
incoming system to around 7000-8000 feet tonight, so will have
another round of rain on snow to impact the snow pack. Snow levels
tumble Friday afternoon once the cold air wrapping around the low
pushes into the region. Snow levels drop to around 4500 ft Friday
afternoon, then to around 3000-3500 ft Saturday and Sunday. Snow
amounts during this time look to be around 1/2 foot at passes Friday
night to Sun day afternoon (48 hours), and closer to 1 ft for the
volcano peaks.

More benign conditions over the weekend into mid next week an upper
trough lingers over the northeast Pacific and Pacific northwest. This
will bring showers at times. Also there is a chance for thunderstorms
over the coastal waters and coast for the weekend. /mh/JLiu

&&

.AVIATION...Expect mainly VFR flight conditions over the next 24
hours. Stratiform rain with a low pressure system offshore will
spread from south to north across northwest Oregon and southwest
Washington tonight while also bringing increasing winds and some
low level wind shear, especially from KSLE to KEUG around 2000 ft.
Winds will be strongest at the coast where gusts up to 45 kt are
possible. Precipitation will become showery Friday morning.
Cannot completely rule out pockets of MVFR cigs Thursday night
through mid Friday morning, however probabilities are generally
less than 20-30%.

PDX APPROACHES...Predominately VFR conditions, however there is a
25-30% chance for MVFR cigs between 12-15z Friday. Persistent rain
will arrive at the terminal towards 08z Friday before transitioning
to off and on light rain showers by 16z. Gusty east to southeast
winds develop tonight with gusts up to approximately 25 kt. -TK

&&

.MARINE...A strong low pressure system will bring rapidly
increasing winds and seas to the waters Thursday night into Friday
morning. Expect gale force winds to develop Thursday night before
quickly ramping up to storm force winds with gusts up to 55 kt by
mid Friday morning. Although winds will be east to southeast
Thursday night, expect winds to veer to the south Friday morning
as the aforementioned low moves northward. With the strong winds,
seas will also build quickly to 20-23 ft. Given a dominant wave
period of only 10 seconds, seas will be very steep and hazardous
through the day. However, seas will begin rapidly falling Friday
night to around 15 ft before falling to 10 to 12 ft by late
Saturday morning. This will be in response to the decreasing winds
during that time as gusts fall to around 25 kt or lower Saturday
morning. This subsiding trend is expected to continue through the
weekend into early next week. In fact, the forecast calls for seas
under 10 ft by Monday with winds around 15-20 kt or less. -TK

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...High Wind Warning from 10 AM to 10 PM PST Friday for ORZ101>103.

     Wind Advisory from 8 AM to 7 PM PST Friday for ORZ114>117.

WA...High Wind Warning from 10 AM to 10 PM PST Friday for WAZ201.

PZ...Gale Warning from 10 PM this evening to 4 AM PST Friday for
     PZZ210-251>253-271>273.

     Storm Warning from 4 AM to 7 PM PST Friday for PZZ210-251>253-
     271>273.
&&

$$

www.weather.gov/portland

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