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Short-term and long-term flood potential for Washington State

Outline . Background information:Monitoring River LevelsAdvisory, Watch and Warning DefinitionsWFO boundaries (public forecast boundaries)Flooding Types (East side vs. West side)Current ConditionsShort Term/Long Term outlooksImpact Summary. Overview . Mountain snowpack greatest since 1998-19

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Short-term and long-term flood potential for Washington State

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    1. Short-term and long-term flood potential for Washington State

    2. Outline Background information: Monitoring River Levels Advisory, Watch and Warning Definitions WFO boundaries (public forecast boundaries) Flooding Types (East side vs. West side) Current Conditions Short Term/Long Term outlooks Impact Summary

    3. Overview Mountain snowpack greatest since 1998-1999 110-160% of normal Enhanced mid to low elevation snowpack Moderate to strong La Nińa to persist through the spring season ? favors wetter than normal conditions Active pattern expected for the next couple of weeks Generally mountain snow and lowland rain Brief periods of warmer temperatures and mountain rain

    4. Monitoring River Levels NWS, USGS, State and Local gages for Washington (~300+) Update frequency 15min - 4 hours Active monitoring via Hydrographs Threshold Alarm

    5. Advisory, Watch and Warning Definitions

    6. NWS/WFO Boundaries

    7. Flooding Types Typical Washington Flood Season Western Washington Oct/Nov through March Eastern Washington Oct/Nov through March, and April through June (snow melt) Western Washington Floods Heavy rainfall is the primary forcing mechanism Impact of snow melt on Western Washington Flooding is secondary Snow melt does not increase the odds of significant flooding occurring, but rather can increase the severity Eastern Washington Floods Forcing mechanism can be snow melt and or heavy rainfall

    8. Current Conditions and Short Term Forecast Snow map (NWRFC) (NOHRSC) Washington Stream Flow Conditions (USGS) Active weather pattern expected for the next couple of weeks (link)

    9. Short Term Enhanced mid and low level snow pack can be an important factor if coupled with heavy rain. Western Washington Chehalis, Skokomish ? heightened risk for minor flooding Eastern Washington Spokane through Palouse (Hangman Creek, Palouse River and many of the tributaries and small streams throughout the area) ? minor flooding expected

    10. Long Term Western Washington None at this time, typically Western Washington flood season winds down by end of March and is not driven by snowmelt Eastern Washington Generally expecting high flows east of the Columbia River Area is more sensitive to precipitation events given expected high flows. Potential for flooding on: Palouse River Stehekin River Klickitat River

    11. Summary Short-term Active period for the next 10-15 days Generally lowland rain and mountain snow Brief periods that are warm enough for mountain rain No blockbuster systems at this time… Long-term No concerns for Western Washington at this time Above normal mountain snowpack definitely a concern for Eastern Washington As always please stay tuned for updates...

    12. Questions

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