ADVISORIES:Major Winds/Rain/Floods/Landslides Coming?

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Long story short: if you live in a valley, near a river or flood zone, or on a bluff above or near a slide zone, you’re SCREWED, as a major storm is moving in and the National Weather Service has issued THREE advisories:

  1. Flood Watch (previously posted here)
  2. Major Wind Advisory
  3. “Special Weather Statement” on increased landslide danger

Here’s the Wind Advisory:

… Wind Advisory in effect until 10 am PST Wednesday…

The National Weather Service in Seattle has issued a Wind Advisory… which is in effect until 10 am PST Wednesday.

A strong storm which is bringing heavy rain to the mountains is also causing strong winds in the Seattle area. These winds will last off and on through the night and diminish Wednesday morning.

Precautionary/preparedness actions…

A Wind Advisory is issued when sustained winds of 30 to 39 mph or gusts of 45 to 57 mph are likely. Winds this strong can snap small tree branches… topple small or shallow-rooted trees… and cause local power outages.

And now, the “Special Weather Statement” regarding heavy rains and the potential for landslides:

… Heavy rain to dramatically increase risk for rainfall induced landslides…

Previous rainfall amounts have been around two to three inches in the Seattle area over the past 18 days. This has resulted in moderate levels of soil moisture around western Washington. Heavy rainfall of nearly two inches in 24 hours and over three inches in 48 hours is expected this afternoon through Wednesday night. This amount of rain will put extra pressure on soil instability leading to an increased risk of landslides in slide prone areas. A diminishing risk of landslides will continue for several days after the rain ends.

The slow melt of the snow that has fallen over the last couple of weeks has had an additional soil wetting effect. In areas outside of Seattle… storm total rainfall could be 3 to 8 inches in The Lowlands and 10 to 20 inches in the mountains. For these reasons the landslide risk is higher than the USGS charts would suggest.

The amount of rainfall forecast in 24 hours… on top of the cumulative rainfall over the last three weeks… will push western Washington soils to the point where they are 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.

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.

If you need help, here’s some info that may come in handy:

  • Sandbags are available for anyone in flood area – check this website here for details
  • King County’s Flood Warning Center is operating; a recorded flood-information hotline is also updated each hour for citizens wanting information in flood areas:
    • Call 206-296-8200 or 1-800-945-9263
    • Citizens who need help interpreting flood information should call 206-296-4535 or 1-800-768-7932
  • Problems on county-maintained roads can be reported by calling 206-296-8100 or 1-800-KC-ROADS

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