Special Weather Statement: Landslide Danger
Special Weather Statement
National Weather Service Seattle Wa
542 am pst Sat Dec 27 2008
Waz001-503>519-281330-
San Juan County-Western Whatcom County-Southwest Interior-East Puget Sound lowlands-Western Skagit County-Everett and vicinity-Seattle Bremerton area-Tacoma area-Admiralty Inlet area-Hood Canal area-Lower Chehalis Valley area-Olympics-Eastern Strait of Juan de Fuca-Western Strait of Juan de Fuca-North Coast-Central Coast-West Slopes Northern Cascades and passes-West Slopes Central Cascades and passes-528 am pst sat dec 27 2008
Rainfall of a quarter of inch to near 1.5 inches over the past 24 hours...combined with melting snow...has resulted in moderate levels of soil moisture around Western Washington. Additional rainfall of a half to near an inch in 24 hours is expected Saturday. This amount of rain will put extra pressure on soil instability leading to an increased risk of landslides.
The amount of rainfall forecast in 24 hours...on top of the cumulative rain and snow melt over the last three weeks...will push Western Washington soils to the point where they are marginally above the USGS landslide index. When cumulative Rainfall exceeds the USGS landslide cumulative threshold index...rainfall induced landslides are possible during intense rainfall or when rainfall amounts exceed two inches in 24 hours.a diminishing risk of landslides will continue for several days after the rain ends.
Areas above 2000 feet in elevation will see mostly snow and not be affected.
While the usgs rainfall thresholds were designed for the Seattle area of the Puget sound...most of the lowlands of Western Washington are similarly susceptible to landslides caused by wet soils. Areas most susceptible to landslides under these conditions are steep coastal bluffs and other steep hillsides.
For more information about current conditions...visit www.weather.gov/seattle...select hydrology...and then scroll down for the link to the usgs landslide information page.
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