...The Flood Warning remains in effect until 145 PM PDT Thursday April 17 for the North Fork stillaguamish river east of the State Route 530 slide in north central Snohomish County...
Flooding continues on the North Fork of the stillaguamish river upstream of the sr 530 slide due to debris from the State Route 530 slide partially blocking the river and the resulting pooling of water behind the debris dam. We will be updating the Flood Warning on a day to day basis.
The latest forecast is a significant change from the last few days. Forecast rainfall amounts for the slide area and mountains are for just under a half inch tonight...three quarters of an inch Wednesday...and one inch Thursday. In response...the river will start rising tonight...then rise sharply Thursday...cresting Thursday night before midnight with the largest flows since the slide occurred. The peak flow forecast for the North Fork river near Arlington gage is near 12000 cfs and near 7700 for the North Fork stillaguamish river at Oso.
At 1000 am PDT...the pool elevation was 284.67 ft.
The pool elevation is forecast to rise to 285.0 ft. By 500 am Thursday then rise sharply to 287.7 ft. By Thursday night before midnight. The pool elevation will start dropping significantly Friday. There is a great amount of uncertainty in the forecast pool elevation crest due in part to limited knowledge of how much water the new stream channel through the slide debris will be able to convey.
For the latest river stages and forecasts...visit (all lower case) water.Weather.Gov/ahps2/index.Php?Wfo=sew or... weather.Gov/Seattle and go to the rivers and lakes section.
A Flood Warning means flooding is occurring or imminent. Most flood related deaths occur in automobiles. Do not attempt to cross water covered bridges...dips...or low water crossings. Never try to cross a flowing stream...even a small one...on foot. To escape rising water move up to higher ground.
Lat...Lon 4825 12181 4829 12185 4829 12177 4829 12166 4824 12165 4826 12174