After a string of warm and sunny days, residents of Western Washington were bracing for the effects of an upper level disturbance coming up from California. The weekend forecast calls for significant rain and possible thunderstorms, with temperatures dropping into the mid-60s.
That change in weather could bring a welcome shift in a longer-term pattern that has allowed a persistent patch of warm water off the West Coast to strengthen in recent weeks, with surface temperatures as much as 3 degrees Fahrenheit above normal.
This phenomenon is referred to colloquially as ‘The Blob’ – a nickname coined by Washington state climatologist Nick Bond, after the pattern started appearing in 2014-15.
Persistent high pressure over the eastern Pacific is what causes it to rev up. Signs of it appeared earlier this year, in March, but quite far offshore. Now it has moved closer to the coast.
“And so The Blob, which was a little bit further offshore, south of the Aleutians, moved inland during the past month or so,” says KNKX weather expert Cliff Mass. “We have warm water over much of the northeast Pacific – and this has strengthened during the last several weeks.”
Mass says the warmth on the surface of the ocean has many effects on local weather. But the most profound one has been clearly evident in recent weeks: a reduction in the amount of cooling that happens overnight, especially in places closer to the coast.
“It tends to keep the minimum temperatures up at night,” Mass says. “And we have seen that on coastal stations like Quillayute and stations around Puget Sound and Boeing Field.”
The effect is less pronounced the further you get from the water and the marine influence on the weather. But clearly, Mass says, The Blob is back — at least for now.
Its appearance causes concern for those who monitor local marine ecosystems. If it stays in place for long, it can severely damage fisheries, bringing economic distress, as it did in 2014-15. Last year, National Oceanic and Atmospheric Administration (NOAA) alerted the public in September that another Northeast Pacific marine heatwave was forming. But it remained shallow and dissipated; the alarm was called off in mid-February.
Mass says it’s a little to early to tell what this one will do. The change in weather coming this week may dislodge the recent pattern of high pressure that tends to fuel The Blob.
“The latest forecasts suggest during the next week, there’s going to be a major circulation change. There will be low pressure or troughing over the eastern Pacific,” Mass says. “And I would expect The Blob to stop strengthening and probably weaken during the next week or two. Beyond that, I really can’t give you much skill on what’s going to happen to The Blob.”
You can listen above to hear the full discussion.
The weekly KNKX feature "Weather with Cliff Mass" airs every Friday at 9 a.m. immediately following BirdNote, and repeats twice on Friday afternoons during All Things Considered. The feature is hosted by KNKX’s Environment reporter Bellamy Pailthorp. Cliff Mass is a University of Washington Professor of Atmospheric Sciences and a renowned Seattle weather prognosticator. You can also subscribe to a podcast of “Weather with Cliff Mass” shows on Apple, Spotify and Google
