The Snohomish, Skykomish, Snoqualmie, Stillaguamish and Sauk-Suiattle rivers were already at, or predicted to climb above, flood stage by today.

The Skykomish River, a tributary to the Snohomish, hit flood stage at 2:30 a.m. Monday near Gold Bar. The North Fork Skykomish in Index hit flood stage about midnight Sunday.

A flood gauge in Arlington showed that the Stillaguamish River hit flood stage about 9 a.m. Monday morning. At I-5, the Stilly hit flood stage about 11 a.m.

What causes the flooding?

Blame the Pineapple Express, a tropical weather system that brings heavy moisture and warm temperatures to the Pacific Northwest.

It works this way: Moisture-laden clouds rush north from tropical areas in the Pacific Ocean, bringing heavy rain to the Cascade Mountains. Flooding is first reported where the heaviest rain falls, usually in mountain areas. That’s why foothill communities such as Index, Granite Falls and Darrington report the first flood damage.

What are the different flood stages?

Normal river flows are considered Phase 1.

A river hits Phase 2 when its banks are full from rain or runoff, and water begins to collect in flood-prone low-lying areas.

Widespread flooding triggering road closures and other disruptions marks Phase 3.

The most severe flooding occurs when rivers reach Phase 4. That is when the rivers can inundate their valleys wall-to-wall. Flowing water threatens to blow out levees. Fast-moving water in upper river channels can migrate and cause erosion.

Experts forecast that all of Snohomish County’s major rivers would reach Phase 4 flooding by sometime today.

What roads should I avoid as I drive to work?

Snohomish County road closures are listed at www.co.snohomish.wa.us. Click on “Emergency Mgmt.” on the left side of the page and then click on “Snohomish County Roads.”

The state Department of Transportation is listing its road closures at: www.wsdot.wa.gov/traffic/weather/updates.

What does flooding mean to fish and other wildlife?

Salmon are now spawning in the rivers. Floodwaters can scour salmon spawning beds, destroying the next generation of fish.

How can I help others?

The Snohomish County Emergency Management Department was accepting help to keep rivers at bay in several locations on Monday. More help will be needed today.

The county has stations for filling sandbags at the Darrington Fire Department, Oso Mill, Robe Fire Station, Sultan Old Duty Hall, and Snohomish Fire Station on Maple Avenue.

Volunteers and people picking up sandbags for themselves should bring their own shovels. For more information, call 425-388-5060.