National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KSEW 280332
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
832 PM PDT Mon Mar 27 2023

.UPDATE...
-- Changed Discussion --
A rather quiet evening has developed across the CWA as
expected. Minuscule shower activity has diminished due to the
cessation of daylight heating. Conditions will become more active
as the overnight progresses with the development of gusty Cascade
gap winds. Areas near and along the Cascade gaps such as
Enumclaw, North Bend, etc. will see sustained winds between 25 to
35 mph with gusts upwards of 50 mph possible late tonight into
Tuesday. No changes have been made to the forecast with the
previous discussion remaining below:
-- End Changed Discussion --

&&

.SYNOPSIS...Warmer and drier weather will persist through mid week
as a strong storm system tracks to the south. A trend back towards
cooler and wetter weather will then return the latter half of the
week and through the weekend as an upper level trough brings the
next chance for widespread rain and a cold front ushers in cooler
air.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...
-- Changed Discussion --
The large scale pattern
this afternoon features a strong area of closed low pressure
centered near 135W and 45N well offshore the WA/OR Coast.
Downstream from this feature exists a weak ridge of high pressure
over the Intermountain West with another broad closed low near
Hudson Bay. Meanwhile, upstream, a ridge of high pressure extends
from the NE Pacific into the Gulf of Alaska with troughing over
the Bering Sea. Near the surface, low pressure corresponds well to
the strong Pacific low initially mentioned, with a stronger
cyclone located to its south with which it is beginning to merge
with (and will soon significantly intensify). Downstream from
this significant feature exists high pressure over much of the
west, with a few weak boundaries over the
Plains/Midwest/Southeast.

It`s a quiet weather day across W WA today as weak high pressure
influences the low levels and the upper closed low over the
Pacific remains displaced well to the west. Abundant sunshine
along with the gradual development of offshore flow has allowed
temperatures to rebound into the 50s. For the rest of today, mid
and high level cloud cover will increase, with increasing offshore
flow/downslope winds off the Cascades as the pressure gradient
tightens between low pressure offshore and higher pressure inland.
Conditions will become windy late this evening and overnight
tonight in the Cascade gaps and East Puget Sound lowlands (where a
wind advisory will remain in place). Isolated power outages and
downed trees will be possible in these areas. Elsewhere, winds
will become breezier.

The strong upper level low and associated strong surface cyclone
will begin to drift towards the N CA Coast on Tuesday, with
easterly/downslope flow peaking across the area into the morning
hours. High clouds will begin to break up over the area, yielding
a period of sunny skies, mostly from southern Puget Sound
northward. Moisture and cloud cover will advect northward from the
low through the day, resulting in increasing cloud cover and even
some areas of light rain scraping Grays Harbor, Lewis, Thurston
and potentially Pierce Counties. High temperatures generally
around 60 in the lowlands but may top off a few degrees cooler in
the counties just mentioned where rain and more persistent cloud
cover are expected.

The upper level low and its sfc reflection will begin to weaken
and sink further south into Wednesday, with wrap around moisture
still expected to linger across Lewis and Pierce Counties,
particularly the southern Cascades. A ridge of upper level high
pressure will begin to build briefly into the area from north to
south on Wednesday, with enough subsidence from it along with high
pressure at the sfc to yield an overall sunny and warm day, with
highs reaching the low 60s. Cloud cover is likely to start to
increase the second half of the day as a weak trough approaches
from the north.

This weak trough will slide across the area on Thursday, but with
a largely continental trajectory, expect minimal moisture with it.
There still could be sufficient lift with it to help generate a
few showers along the coast and higher terrain. Cooler weather
will follow with it with high temperatures a good 5 degrees cooler
in the mid 50s.

This will then give way to much more active and cooler weather in
the long term period.

Kovacik

.LONG TERM /FRIDAY THROUGH MONDAY/...On Friday, an area of low
pressure will deepen over the Gulf of Alaska, with a shortwave
ejecting out of its southern periphery towards the Pacific
Northwest. This system will carry a surface frontal boundary with
it, bringing the next chance for organized widespread lowland rain
and heavy mountain snow to the area.

Rain looks to arrive around the Coast Friday afternoon and evening
and quickly spread inland through the overnight period into early
Saturday. The system will give way to scattered showers across
the area through the day Saturday and with cooler mid level
temperatures, could support convection. Showery and cooler weather
looks to continue through the rest of the weekend and into early
next week as upper troughing remains in place. High temps for the
lowlands trend back to the upper 40s/near 50 for highs while lows
dip into the low-mid 30s. Snow levels hover around 1000ft so not
expecting a rain/snow mix potential for the lowlands at this time,
but widespread mountain snow showers could be heavy at times.

Kovacik
-- End Changed Discussion --

&&

.AVIATION...
-- Changed Discussion --
A broad upper trough continues to move southward over
the offshore waters with southerly flow aloft becoming more easterly
on Tuesday. High and mid clouds continue to increase across southern
portions of the area with high/mid clouds through tonight. VFR cigs
with light rain possible along and south of KHQM-KOLM into early
Tuesday. VFR cigs Tuesday. Increasing low level offshore flow
tonight through Tuesday with gusty E/NE surface winds, especially
near the gaps in terrain.

KSEA...VFR cigs with high and mid level clouds continuing to
increase tonight. VFR on Tuesday. Surface winds easterly with some
NE winds into tonight. Gusty winds to 25 to 30 kts possible late
tonight and through Tuesday. JD
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
A strengthening surface low along the offshore waters will
continue to deepen tonight over the Oregon offshore waters with a
strengthening ridge over the interior British Columbia area.
Increasing low level offshore flow tonight into Tuesday. Small Craft
Advisory winds likely for most waters tonight through early Tuesday
afternoon. Gale Warning has been issued for the northern inner
Coastal Waters and the western Strait of Juan de Fuca late tonight
through Tuesday morning where offshore winds will likely be
strongest. Brief gales are possible elsewhere along the Coastal
Waters and central Strait of Juan de Fuca. Winds will gradually ease
Tuesday night into Wednesday as the offshore low weakens and shifts
well south of the area. Generally lighter winds Wednesday into
Thursday with brief periods of stronger west winds through the
central and eastern Strait of Juan de Fuca. Another frontal system
will move into the area on Friday.

Combined seas will generally be 3 to 5 feet through tonight and
build to 6 to 9 feet on Tuesday with a S/SW swell. Seas briefly to
10 feet are possible across the southern tier of the area Tuesday. JD
-- End Changed Discussion --

&&

.HYDROLOGY...No river flooding expected the next 7 days.


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
WA...Wind Advisory until 5 PM PDT Tuesday for East Puget Sound
     Lowlands.

PZ...Small Craft Advisory until 3 AM PDT Tuesday for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Gale Warning from 3 AM to 2 PM PDT Tuesday for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 8 PM PDT Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 8 PM PDT Tuesday for Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory from 9 AM to 5 PM PDT Tuesday for Puget
     Sound and Hood Canal.

     Small Craft Advisory until 2 PM PDT Tuesday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From James Island To Point Grenville Out 10
     Nm-Coastal Waters From Point Grenville To Cape Shoalwater
     10 To 60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater Out 10 Nm.
-- End Changed Discussion --

&&

$$