Heavy Snow in Washington, April 15 to 18, 2023

Area Forecast Discussion
National Weather Service Seattle WA
900 AM PDT Sat Apr 15 2023

.SYNOPSIS...Increasing clouds with light rain spreading onshore
through the day. A front will follow late tonight into Tuesday
with lowland rain and mountain snow. Unsettled weather likely to
continue through at least the first half of next week as
additional disturbances cross the Pacific Northwest, maintaining
cool and occasionally wet conditions.

&&

.SHORT TERM /TODAY THROUGH MONDAY/...No updates made to the
forecast this morning as everything is on track. Previous
discussions can be found below.

The leading rain associated with our next disturbance is already
pushing into the coast this morning, with rain reported at both
Quillayute and Hoquiam at this hour. This will continue to spread
east through the day, likely filling most of Western Washington by
late afternoon. Snow levels will rise a bit in the warm sector,
with mostly rain over the Cascade passes today. Temperatures will
continue to remain on the cool side, remaining below seasonal
normal. Expect the cold front to reach the coast late tonight or
early Sunday, with a cool, damp day across the region. Behind the
front, expect showers to continue is the unstable post-frontal air
mass. Precipitation will transition over to snow at pass level,
though amounts don't look too significant as moisture fades.
However, while confidence is low, there remains some potential
(10-15% chance) for an isolated thunderstorm or two to develop
late Sunday

Little change to the overall pattern, as the next disturbance
rounding the upper low will bring a round of more widespread
showers. This system doesn't look as impressive with respect to
QPF, but again expect a cooler and wet day for many. Some areas in
the northern/central Sound may end up with only a few showers
though as the region remains initially shadowed. There will again
be a small (10-15%) chance for isolated thunderstorms, though
chances Monday are more confined to the coast and areas south of
Puget Sound.

.LONG TERM /TUESDAY THROUGH FRIDAY/...Ensemble guidance continues
to maintain upper level low pressure across the region through the
midweek time period. A few impulses are likely to bring rounds of
showers and temperatures likely below normal. Latest cluster
analysis might lend some hope for warming/drying late in the week
next week with around half of ensemble members suggesting higher
pressure building. However, the other half of the members support
more of a zonal or even northwesterly flow pattern. So, suffice it
to say that confidence is not particularly high in this potentially
warmer and drier pattern emerging.    Cullen

&&

.AVIATION...Southwesterly flow aloft with large upper level
trough offshore through the weekend. Surface high pressure over
the area this morning will shift east this afternoon. Approaching
front stalling over the coastal waters tonight before moving
inland Sunday.

Foe the interior ceilings aoa 10000 feet lowering to 3500-4500
feet 21z-00z. Ceilings remaining in the 3500-4500 foot range into
Sunday morning. For the coast MVFR ceilings through Sunday
morning.

KSEA...Ceilings aoa 10000 feet lowering to 3500-4500 feet
21z-00z. Ceilings remaining in the 3500-4500 foot range into
Sunday morning. South wind 4 to 8 knots. Felton

&&

.MARINE...Surface high pressure over the waters this morning will
shift east this afternoon. Approaching front stalling over the
coastal waters tonight before moving inland Sunday. Next surface
low, near 1000 mb, will move through the offshore waters Monday on
its way to Vancouver Island. Lower pressure will remain over the
waters Tuesday with weak high pressure building Wednesday.

Small craft advisory winds over the coastal waters through the
weekend into Monday.

Small craft advisory winds developing in the Strait, Admiralty
Inlet and Northern Inland waters this evening continuing into
Sunday. Small craft advisory winds over all the inland waters
Sunday afternoon as the front moves through the area. Winds easing
behind the front Sunday evening except in the central and eastern
Strait of Juan de Fuca where small craft advisory post frontal
westerlies are in the forecast. Another round of small craft
advisory winds Monday for the waters. Felton

&&

.HYDROLOGY...No river flooding is expected during the next seven days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from noon today to 2 AM PDT Sunday for West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from midnight tonight to 6 PM PDT Sunday
     for Admiralty Inlet-East Entrance U.S. Waters Strait Of
     Juan De Fuca-Northern Inland Waters Including The San Juan
     Islands.

     Small Craft Advisory until 6 PM PDT Sunday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From Cape Flattery To James Island Out 10 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.

&&