SEATTLE - Landslides are the unfortunate combination of too much rain mixed with gravity. When the ground gets saturated on a slope, it can cut loose, and everything that sits on it from homes to trees, cars and people can head downhill along with the dirt.
The worst winter wasn't that long ago. It was in 1996-1997 when Seattle had 300 slides in one winter, including the disasterous damage where part of the neighborhood along Perkins Lane headed downhill. Homes, some built back in the 1930s, ended up on the beach below.
That reality, along with a century of history of landslides and weather records in Seattle, provided the perfect opportunity for geo scientists at the U.S. Geological Survey to come up wiith a tool that would help Seattle predict when we had entered "the zone."
That tool is a threshold, a simple angled line on a computer that helps judge just how much at risk the city is of having more landslides. Under the threshold, the risk is low, over the threshold the risks go up. Right now, Seattle is on the line. Gig Harbor is over it as measured by rain falling at the Tacoma Narrows Airport.
It could be worse.
Even though much of Western Washington is plowing through a multi-day streatch of rain, this winter has been pretty forgiving. In fact, because of El Nino our weather pattern has been relatively dry and warm this winter.