RAIN SOAKED SOILS LEAVE INCREASED RISK OF LANDSLIDES IN WESTERN WASHINGTON
Plus flood warnings
January 15, 2011
(MONROE, WA) -- The National Weather Service office in Seattle issued a Flood Warning for the Snoqualmie river near Carnation just after 5:00m pm Friday evening and lasting under Saturday afternoon.
At 4:30 PM Friday the flood stage was at 53.7 feet and the stage at wich minor flooding occurres is 54.0 feet. Minor flooding is forecast.
The river was expected to rise above flood stage around 7:00 om Friday and crest near 54.6 feet around 4 am Saturday. The river will fall below flood stage Saturday morning.
At 54.0 feet the Snoqualmie river will flood much of the farm land and several roads from Fall City downstream through Carnation and Duvall.
FLOOD WATCH FOR OTHER AREAS
A Flood Watch remains in effect through Sunday afternoon for portions of western Washington including the following counties thorugh Sunday afternoon:
Grays Harbor... Clallam... Jefferson... Skagit... Whatcom... King... Lewis... Mason... Pierce...Snohomish...Thurston.
A series of warm and wet weather systems has brought the rivers up to well above normal flows. One more frontal system will move through the region Saturday night and Sunday.
This last frontal system is likely to be the wettest and warmest of the series with a
snow level around 7000 feet by Sunday.
The National Weather Service released a statement Friday saying that the large amounts of rain – rainfall of generally a half to 1.5 inches during the 24-hour period from noon Thursday to noon Friday - has made the soils in western Washington more saturated.
And that has led to an increased risk of landslides.
In the past three days, 1 to 3 inches of rain has fallen with amounts of 4 to 6 inches observed in the mountains. Additional rainfall of 1 to 2.5 inches is expected on the lowlands by late Sunday, with amounts of up to 6 inches anticipated in the mountains.
This amount of rain will put extra pressure on soil instability, leading to an increased risk of landslides.
When he cumulative rainfall exceeds the USGS landslide cumulative threshold index, then 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.
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.
RECORD TEMP SET IN SEATTLE
A record high temperature of 55 degrees was set in Seattle Friday.This breaks the old record of 54 set in 1988.
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