NEW FLOOD WATCH
FOR SKY VALLEY:
MAJOR FLOODING EXPECTED!
November 11, 2008
(WESTERN WA) -- The National Weather Service issued a FLOOD WATCH for possible heavy flooding on rivers in the Sky Valley and general Snohomish county area at 4:19 a.m. this morning. The flood watch remains in effect from 4:00 p.m. this afternoon through Late Wednesday evening.
Flooding in downtown Sultan in flood of NOV 6, 2006. Statue of Sultan John in middle of frame. (Staff photo)
The flood watch also covers rivers in Grays Harbor, Clallam, Jefferson and Skagit counties as well as Whatcom, King, Kitsap, Lewis, Mason, Pierce and Thurston counties.
Forecasters say a series of storm fronts is expected to hit Western Washington and drop up to a foot or more of rain in some areas between later on today and early Wednesday.
From 4:00 p.m. onward today and through late Wednesday night the first of a series of storm fronts that will affect the region into Wednesday will be pushing onshore in the state.
In the first storm front snow levels will start out around 4,000 feet then rise to over 6,000 feet this afternoon. This front is expected to produce between one and two inches of precipitation over the mountains.
A second, stronger storm front that is drawing with it tropical moisture that will raise the freezing levels to around 10,000 feet and spread heavier rain across the area tonight into Wednesday. The combination of a strong westerly wind in the mid levels of the atmosphere and abundant moisture is expected to produce very heavy rain along the west slopes of the Olympics and Cascades.
Rainfall amounts over the Olympics and Cascade mountains are expected to range from 3 to 7 inches and may locally exceed 10 inches. A Flood Watch means there is a potential for flooding based on the current forecasts. Residents in the flood watch areas should be aware of the potential for significant rainfall that could lead to flooding and be prepared to take action should flooding develop.
Forecast models indicate the Skykomish River near Gold Bar may hit flood stage tomorrow morning and peak at around 17 feet Wednesday afternoon sometime.
The Snohomish River at Monroe is forecast to flood Wednesday afternoon and peak later that evening at around at 19.5 feet. At the town of Snohomish the river is expected to flood over banks tomorrow afternoon and crest at a little over 30 feet by Thursday morning.
Residents can expect floodwaters from the Snohomish River to flood some low lying farmland and a number of roads including the old Snohomish-Monroe Highway and Riverview Road.
The large flood of 1990 saw the Snohomish River at Monroe crest at 14 feet above the 19.5 feet flood stage prediction for Wednesday and Thursday and the large flood of November 6, 2006 that saw the river crest at 33.5 feet.
In Sultan, where the swollen Sultan and Skykomish rivers often back up and flood a portion of the downtown area near the Sultan River Bridge, residents may obtain sand bags supplied by the city. The bags will be located behind the public works building at 703 First St.
THEAT OF LANDSLIDES WITH THE HEAVY RAIN
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.
The National Weather Service says a large part of western Washington will receive heavy rain over the next 24 to 36 hours increasing the threat of landslides tonight through Thursday. This includes the Olympics and west slopes of the Cascades, the coast of Washington state, the western Strait of Juan de Fuca and much of the southwest interior.
A diminishing risk of landslides will continue for several days after the rain ends.
Due to a rain shadow northeast and east of the Olympics the central Puget Sound, Admiralty Inlet and eastern Strait of Juan de Fuca will not receive the heavy rainfall and thus will likely not have a threat of landslides.
This area of little or no threat includes the Seattle to Everett Metro area, the Kitsap Peninsula north of Belfair, the Strait of Juan de Fuca east of Joyce, Whidbey Island and the San Juan Islands.
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 up to the minute landslide warnings visit www.Weather.Gov/Seattle, then select hydrology and then scroll down for the link to the USGS landslide information Page.
Residents in the Sultan area may access real time flood data on the web at http://www.ci.sultan.wa.us/Live/Environment/Flood_Information/ and real time Snohomish County road closures at http://www.co.snohomish.wa.us/PWApp/roads/emclosure/index.html.
Real time flood information from the U.S. Geological Service is available at http://water.usgs.gov/waterwatch/?m=flood&r=wa&w=map.