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2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br /> <br /> <br />Chapter 4: Hazard Identification and Risk Assessment 73 <br />Table 4-24. Northwest Avalanche Center Avalanche Advisories <br />Type Definition <br />Special Avalanche <br />Bulletin <br />Issued when significant public use is expected and dangerous avalanche conditions <br />exist, but the avalanche conditions do not meet the level necessary to issue an <br />Avalanche Warning. This is an impact-based product. <br />Avalanche Watch <br />Issued when there is high confidence that warning conditions will develop within 24 <br />and 48 hours of the forecast issuance. An Avalanche Watch will likely be upgraded <br />to a warning closer to the anticipated event. <br />Avalanche Warning <br />Issued when High avalanche danger is expected within 24 hours of the forecast <br />issuance for many areas. Many areas can mean very large geographic areas or <br />several aspects and/or elevations in a specific geographic area. Avalanche Warnings <br />are not issued when the danger is high in specific or isolated areas. Furthermore, <br />warnings can be issued when non-recreationalists or people who would not otherwise <br />access the avalanche forecast are expected to be adversely impacted. <br /> <br />NWAC will always issue an avalanche warning when the danger is at least High or <br />Extreme (per the NAPADS) in all three (3) elevation bands – below treeline, near <br />treeline and above treeline. <br />4.6.1.4. Probability and Frequency <br />The probability of occurrence for an avalanche occurring in Kittitas County is high because avalanche <br />events occur annually. According to the 2023 Washington State Enhanced Hazard Mitigation Plan, the <br />probability of a future avalanche related disaster declarations each year is less than 1% in the State. <br />Avalanches occur regularly every year in mountain areas. Many weather and terrain factors determine <br />avalanche danger. At lower elevations of the Cascades, the avalanche season begins in November and <br />continues until the last remnants of snow have melted in early summer. In the high alpine regions, the <br />hazard continues year round. Hundreds of thousands of avalanches are thought to occur each year in <br />the Cascades. While the probability of avalanches occurring each year is very high, there is a very low <br />impact on the planning area due to the remote locations of events and mitigation efforts along developed <br />areas. Avalanches along two (2) main mountain highway passes are limited due to ongoing mitigation to <br />control slides during the winter months. <br /> <br />The avalanche annualized frequency value represents the average number of recorded avalanche <br />hazard occurrences, in event days, per year over the period of record. Table 4-25 outlines the annualized <br />frequency for avalanches, based on FEMA NRI data, for Kittitas County. <br />Table 4-25. Avalanche Annualized Frequency (FEMA National Risk Index) <br />Location Events on Record <br />(1960 – 2019) Annualized Frequency <br />Kittitas County 7 0.1 events per year <br />Annualized frequency is defined as the expected frequency or probability of a hazard occurrence per year. <br />4.6.1.5. Past Events <br />Avalanches occur frequently each year and kill, on average, one (1) to two (2) people annually in <br />Washington and about 28 people annually in the United States.62F <br />63, <br />63F <br />64 Avalanches have killed more people <br />in Washington than any other hazard during the past century. In 90% of avalanche fatalities, the weight <br /> <br />63 Washington Emergency Management Division. (n.d.). Avalanche. Retrieved from https://mil.wa.gov/avalanche. <br />64 Federal Emergency Management Agency. (n.d.). Avalanche: Impact. Retrieved from <br />https://community.fema.gov/ProtectiveActions/s/article/Avalanche-Impact.