Cliff Mass investigates landslides, finds possible culprit

Apr 12, 2013

There's more rain in the forecast tonight and this weekend -- with some real downpours expected Saturday in the fabled "convergence zone" of south Everett.

The rain should arrive after 4pm today, for much of the Puget Sound region, says Cliff Mass, professor of Atmospheric Sciences at the University of Washington (and KPLU's weekly weather expert).

Could that mean more landslides, like the ones that have derailed trains south of Everett, or pulled away a home on Whidbey Island?

The truth is, the overall rainfall the past couple months is about normal. Wondering if there could be more to the story, Mass pulled together more rain data, going back months and years.

What he found: The area that's had the most landslides had an exceptionally wet period last November and December -- getting 130% more rain than an average year. One weather station had it's wettest December since 1933.

Even though it was about average in the period from January through March, that rain might have set the stage for the landslides that started a few weeks ago.

"I'm no geomorphologist," says Mass. "[But,] somehow the cumulative rainfall over this period of six months must have had an impact."

He spells out in detail how all this adds up in a blog post.

And, by the way, for this weekend, Mass reminds us that the convergence zone extends east into the mountains, so he predicts there will be a big dump of snow in area around Stevens Pass and the Alpine Lakes Wilderness. The front should move through by Sunday, but the temperatures will remain cool until Monday, he says. (For more details on the forecast, click the "listen" button above.)

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Do you have a weather question? Cliff Mass and Keith Seinfeld occasionally answer reader questions on the air. Share yours here.

The weekly KPLU 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 KPLU’s Science and Health reporter Keith Seinfeld. Cliff Mass is a University of Washington Professor of Atmospheric Sciences, a renowned Seattle weather prognosticator, and a popular weather blogger. You can also subscribe to a podcast of “Weather with Cliff Mass” shows.