Floods can occur in any month, but most commonly occur between November and February during periods of heavy rain or rapid snow melt. During a flood, agencies respond in four phases depending on the severity of expected flooding, with Phase 4 being the most severe.
During phases 2, 3, 4, flood updates and warnings are reported to police, fire departments, schools, other agencies, and news media.
See left sidebar for phase and river levels at gauge sites in Snohomish County.
Phase Definitions
| Phase 1 | - Actual flooding is rare
- County staff is put on alert
- Preparations are made to open the county's Emergency Operations Center
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| Phase 2 | - Minor flooding and some road closures may occur
- The county Emergency Operation Center opens
- Staff begins monitoring river gauges and flood conditions around the clock
- Flood information phone lines are updated hourly with current river gauge / river level information
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| Phase 3 | - Moderate to severe flooding, with numerous road closures and some levee overtopping can be expected
- Investigation crews are sent to monitor flood control facilities such as levees
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| Phase 4 | - All agencies respond in anticipation of major flooding and widespread damage
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