San Juan Islands and Northern Inland Waters Marine Forecast (2024)

Synopsis
A weak shortwave will produce spotty showers to the Olympic and Cascade mountains through this afternoon and evening along with the potential for elevated thunderstorms. An upper level trough moving into British Columbia into the first half of the week will cool temperatures closer to seasonal norms and increase night and morning cloudiness.

Short Term - Today through Tuesday
Upper level ridging will shift eastward later this morning allowing for a broad upper level trough offshore to nudge closer to western Washington. This will allow for stratus to spread inland this morning, clipping Puget Sound. Stratus will burn back by the afternoon, but will allow temperatures to be cooler today, with locations in the interior generally in the low to mid 80s this afternoon, and coastal locations in the mid 60s.

The aforementioned upper level trough will eject a weak shortwave through our area later this morning into the afternoon. Hi- resolution guidance suggest activity starting early this afternoon along the coast and the Olympics, then moving eastward into the Cascades. Model guidance lands mid- level lapse rates in the 7-8 C/km range, which would support elevated thunderstorms in the mountains. Moisture is very limited, but with southerly flow, these factors can definitely help kickstart a thunderstorm, especially with diurnal heating. The main concern with any thunderstorm that does develop is the risk for lightning and erratic winds, for fuels remain very dry in both the Olympics and the Cascades. See the fire weather section below for more information regarding fire weather.

Any thunderstorm potential will end by tonight as instability values vanish and diurnal heating ends. Low level onshore flow will increase into Monday and Tuesday as broad upper level troughing takes over. Normal temperatures will return over western Washington, with highs in the interior in the mid to upper 70s, and 60s for coastal locations. Morning cloudiness will be likely each day with periods of sun in the afternoon.

Long Term - Wednesday Through Saturday
Broad upper level troughing remains situated over the Pacific Northwest through the long term, with varying degrees of onshore flow, morning stratus, and temperatures hovering around normal. As of right now, no significant weather is expected through the long term (and no precipitation).

Mazurkiewicz

Marine
Broad surface ridging will remain situated over the offshore waters with lower pressure east of the Cascades through much of the week ahead. A series of weak upper troughs moving into British Columbia will increase the onshore flow at times. Strengthening onshore flow today ahead of the first of these is expected to produce westerly gales in the central/east strait by this evening. Additionally, northwesterlies will increase across the coastal waters. A small craft advisory has been posted for the southern portion of the outer coastal waters for a combination of choppy seas and wind. This could be expanded to a larger portion of the coastal waters if conditions warrant. Persistent onshore flow will likely necessitate additional headlines for the strait and portions of the coastal waters in the days ahead. 27

Fire Weather
A Red Flag Warning will continue for zones 652, 661, 658, and 659 through Monday morning. A weak disturbance will bring the potential for scattered elevated thunderstorms over receptive fuels, particularly this afternoon into the evening hours. All it takes is one lightning strike to ignite a fire on such dry fuels. Convective activity should end by late tonight possibly into early Monday morning. Will continue to monitor the situation as the conditions evolve. A cooler and more humid pattern develops Monday as an upper level trough settles over the region.

NOAA Seattle WA Office: Watches - Warnings - Advisories
WA...Red Flag Warning from 5am early this morning to 6pm PDT this evening for East Portion of the Olympic Mountains-West Portion of the Olympic Mountains.

Red Flag Warning from 8am this morning to 5am PDT Monday for West Slopes of the Central Cascades Generally above 1500 Feet-West Slopes of the North Cascades Generally above 1500 Feet.

PZ...Gale Warning from 5pm this afternoon to 3am PDT Monday for
Central U.S. Waters Strait Of Juan De Fuca-
East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 5pm PDT this afternoon for
Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.