590
FXUS66 KSEW 012141
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
241 PM PDT Wed May 1 2024

.SYNOPSIS...Another weak system will slide to the south late
Wednesday into Thursday, bringing in light shower activity. Drier
and warmer conditions are expected Thursday and Friday before more
precipitation arrives in time for the weekend and beyond.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...A weak frontal system
will clip SW WA tonight for a chance of rain (mainly coast and
south of Olympia). We`re seeing a mix of mid and high clouds on
satellite associated with this system with sunnier skies toward
the north. Temperatures will be chilly again overnight and in the
mid to upper 30s over the south sound. Patchy frost is possible
although should be brief.

A weak ridge will build offshore on Thursday and we`re looking for
mainly dry weather for western WA. We could see a few pop-up
showers in the Cascades otherwise dry in the lowlands. The air
mass will be a little warmer with temperatures in the 60s. The
ridge axis moves inland Thursday night with dry weather
continuing.

The pattern changes as we move into Friday. By then the ridge
shifts farther east and inland while a deep upper low settles down
over the NE Pac. Attached to this low is a frontal boundary with
rain reaching the coast in the morning then spreading inland
during the afternoon.

The upper low shifts south off the coast on Saturday but we`re
still under moist/diffluent flow over western WA. This looks like
more rain spreading over the region through much of the day (and
not much of a break). With cooler and cloudier conditions we`re
only expecting highs in the lower to mid 50s. 33

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...The broad upper level low
shifts inland over the weekend and is still meandering over the
West as we move into Sunday. There`s still plenty of wrap-around
moisture moving into western WA with additional showers expected.
Snow levels are around 4500 ft for rain at the Cascade passes.
Moving on, we`re under solid onshore flow early next week keeping
us cool and wet through the period. Onshore flow eases by
Wednesday and drier N/NW flow may give us a brief break in the
action. 33

&&

.AVIATION...A weak low pressure system will continue to shift
southward away from western Washington this evening, with
northerly flow aloft prevailing. Mostly VFR at all terminals this
afternoon, with some mid to high level clouds streaming in along
the coast and south of Olympia. Otherwise, this trend will
continue through the evening and into the overnight period where
VFR will continue with likely clear skies. Latest guidance
suggest some patchy fog to develop within the Southwest Interior
and possibly near central Puget Sound, with at least a 20-25% of
MVFR conditions early Thursday morning (09z-14z). Low level winds
will remain S/SW this afternoon before switching to the north
around 03z and staying around 4 to 8 knots.

KSEA...VFR conditions this afternoon as just some mid to high
level clouds linger around. Clouds will eventually break apart
for clear skies tonight with VFR continuing. Some patchy fog may
be possible early Thursday morning in the vicinity of the terminal
around 11z-14z, but there is a 20% chance of MVFR conditions if
fog were to develop. S/SW winds this afternoon around 5 to 10
knots will shift to the north around 03z-05z this evening and
generally maintain the same speeds through Thursday morning.

Maz

&&

.MARINE...Onshore flow will continue this afternoon with surface
high pressure over the coastal waters. A weak low pressure system
will continue to move south into the Oregon border tonight,
allowing for winds over the coastal waters to increase and turn
southerly. Latest guidance keeps winds over the coastal waters
around 10 to 20 kts, remaining under any headline thresholds.

Weak high pressure will move through the waters Thursday into
Friday, before a stronger system moves in Friday into Saturday
with small craft southerlies. Another system looks to move
through during the weekend.

Combined seas this afternoon are around 5 to 7 feet and will
subside to around 3 to 5 feet tonight. Seas will remain 3 to 5
feet before increasing on Friday.

Maz

&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$