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2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br />Extreme lmpacts <br />Expect substantial disruptions to daily life. <br />o Extremely dangerous or impossible driving conditions. Travel is not <br />advised. <br />o Extensive and widespread closures and disruptions to infrastructure <br />may occur.o Life-savinq actions may be needed. <br />lndex Description <br />The Sperry-Piltz lce Accumulation lndex (SPIA lndex) is a decision support tool that estimates ice <br />accumulation and potential ice damage from incoming ice storms. lt uses an algorithm of researched <br />parameters that, when combined with NWS forecast data, it estimates the projected footprint, total ice <br />accumulation, and potential damage resulting from approaching ice storms. The SPIA lndex categories <br />of damage, as listed in Table 4-153, are based upon a combination of precipitation totals, temperatures, <br />and wind speeds/direction.265 <br />Table 4-153. Sperry-Piltz lce Accumulation Index <br />265 Sperry, S. and Piltz, S. (2011). The SPIA lndex. Retrieved from <br />https://www.weather.sov/media/ffc/iM201 4/lWT201 4 Sperrv.pdf . <br />Less than 15 Minimal risk of damage to exposed utility systems. No <br />alerts or advisories are needed for crews. Few outaoes.Less than 0.25 <br />0.10 - 0.25 15 -25 <br />1 <br />0.25 - 0.50 Less than 15 <br />Some isolated or localized utility interruptions are <br />possible, typically lasting only a few hours. Roads and <br />bridqes mav become slick and hazardous. <br />0.10 - 0.25 25 -35 <br />15 -250.25 - 0.50 <br />0.50 - 0.75 Less than 15 <br />Scattered utility interruptions expected, typically lasting <br />12 to 24 hours. Roads and travel conditions may be <br />extremely hazardous due to ice accumulations. <br />0.10 - 0.25 Greater than <br />or equal to 35 <br />25 -350.25 - 0.50 <br />0.50 - 0.75 15 -25 <br />0.75 - 1.00 Less than 15 <br />Numerous utility interruptions with some damage to <br />main feeder lines and equipment expected. Tree limb <br />damage is excessive. Outages lasting one (1) to five <br />(5) days. <br />0.25 - 0.50 Greater than <br />or equalto 35 <br />0.50 - 0.75 25 -35 <br />0.75 - 1.00 15-25 <br />1.00 - 1 .50 Less than 15 <br />Prolonged and widespread utility interruptions with <br />extensive damage to main distribution feeder lines and <br />some high voltage transmission lines/structures. <br />Outages lasting five (5) to 10 days. <br />Greater than <br />or equalto 350.50 - 0.75 <br />0.75 - 1.00 Greater than <br />or equalto 25 <br />1.00 - 1.50 Greater than <br />orequalto 15 <br />Greater than 1.50 Any <br />Catastrophic damage to the entire exposed utility <br />systems, including both distribution and transmission <br />networks. Outages could last several weeks in some <br />areas. Shelters are needed. <br />lce <br />Damage <br />lndex <br />Average NWS <br />lce Amount <br />(inches) <br />Damage and lmpact DescriptionWind <br />(mph) <br />Chapter 4: Hazard ldentification and Risk Assessment 204