919
FXUS66 KSEW 170332
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
832 PM PDT Thu May 16 2024

.SYNOPSIS...Upper-level troughing through much of the upcoming
weekend. With it, cooler and showery conditions are in store.
Brief ridging is expected to start the upcoming week before
troughing rebounds through the middle of next week.

&&

.UPDATE...Convergence zone showers continue across Snohomish
County this evening. Hi-Res guidance shows the activity spreading
south into King county late into the evening before dissipating
overnight. Precipitation forecast is on track, so no major changes
to the forecast below (minus a refreshed aviation discussion).

HPR

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...As mentioned, upper-
troughing is currently positioned over the region. At the surface,
a frontal boundary is pushing towards western Washington out of
BC. With it, increased onshore flow and spotty precipitation is
being observed across the area. Light rain showers are in the
forecast this evening along with convergence activity. Most of the
precipitation will fall in higher elevations with aid of
orographic enhancement. High-res guidance has the PSCZ focused
mainly over Snohomish County before drifting southwards over King
County overnight tonight. With troughing overhead, cooler temps
aloft are expected with snow levels around 3,000-3,500 ft.
Overnight lows are to fall into the low to mid 40s.

Lingering showers are possible into Friday as we`ll be on the
backside of the upper-trough. Nevertheless, drier conditions are
expected but cooler temps are to remain with highs slightly below
average. Then, the next upper-low is on track to enter on Saturday
with another round of showers. However, a drying will try to set
up on later on Sunday as transient ridging moves overhead by the
nighttime hours. Weekend highs are to top out in the mid 50s to
lower 60s with overnight lows in the 40s.

.LONG TERM /MONDAY THROUGH THURSDAY/...Ridging to remain over the
region on Monday but it won`t be long lasting. Active weather
looks to resume around the Tuesday-Wednesday timeframe as another
upper-low out of BC dives south into the region. Temperatures are
to be around average for Monday but, cooler temps along with wet
weather looks to pick back up as the week continues.

McMillian

&&

.AVIATION...Westerly flow aloft will continue as an upper trough
moves across the Pacific Northwest. Post-frontal airmass continues
this evening with a convergence zone located across portions of
Snohomish and King Counties. Generally VFR this evening with areas
of MVFR with isolated showers, and MVFR/IFR near the convergence
zone. The convergence zone will slowly slide southward across King
County and into the Cascades tonight, with shower activity mainly in
the Cascades tonight. BKN VFR tonight with areas of MVFR and some
clearing as well. High end MVFR to low end VFR possible into the
morning, particularly east of Puget Sound. Otherwise, continued VFR
into the afternoon. Breezy SW to NW winds this evening will taper
tonight.

KSEA...VFR cigs this evening with a convergence zone north of SEA.
Generally SCT/BKN VFR tonight into Friday. Shower activity mainly in
the Cascades tonight. Brief period of high end MVFR possible Friday
morning, but confidence is low. Winds will primarily be southerly
into Friday, but should note at least a slight chance of VRB winds
tonight, mainly between 05-08z as the convergence zone moves
southward. JD

&&

.MARINE...An incoming frontal system will keep conditions breezy
across the area waters into Friday. Small craft advisories will be
in effect for all area waters as a result. Seas across the coastal
waters will build towards 10 ft on Friday, likely resulting in an
extension of small craft headlines for the coastal waters zones.
High pressure offshore looks to remain persistent into next week.
With lower pressure situated inland, expect onshore flow to
persist through the forecast period. Another frontal system looks
to move across the area waters early next week and may result in
another round of headlines.

Seas currently hovering at 4-6 ft over the coastal waters this
afternoon. Expect seas to build towards 9-12 ft on Friday before
gradually subsiding back to 5-7 ft over the weekend and into early
next week. 14

&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 11 AM PDT Friday for Admiralty Inlet-
     Central U.S. Waters Strait Of Juan De Fuca-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-East Entrance U.S. Waters Strait Of
     Juan De Fuca-Northern Inland Waters Including The San Juan
     Islands-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 5 AM PDT Friday for Puget Sound and
     Hood Canal.

&&

$$