Laserfiche WebLink
2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br /> <br /> <br />Chapter 4: Hazard Identification and Risk Assessment 200 <br />Index Description <br /> Extreme Impacts <br />Expect substantial disruptions to daily life. <br />• Extremely dangerous or impossible driving conditions. Travel is not <br />advised. <br />• Extensive and widespread closures and disruptions to infrastructure <br />may occur. <br />• Life-saving actions may be needed. <br /> <br />The Sperry–Piltz Ice Accumulation Index (SPIA Index) is a decision support tool that estimates ice <br />accumulation and potential ice damage from incoming ice storms. It 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 Index 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 Ice Accumulation Index <br />Ice <br />Damage <br />Index <br />Average NWS <br />Ice Amount <br />(inches) <br />Wind <br />(mph) Damage and Impact Description <br />0 Less than 0.25 Less than 15 Minimal risk of damage to exposed utility systems . No <br />alerts or advisories are needed for crews. Few outages. <br />1 0.10 – 0.25 15 – 25 Some isolated or localized utility interruptions are <br />possible, typically lasting only a few hours. Roads and <br />bridges may become slick and hazardous. 0.25 – 0.50 Less than 15 <br />2 <br />0.10 – 0.25 25 – 35 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 />0.25 – 0.50 15 – 25 <br />0.50 – 0.75 Less than 15 <br />3 <br />0.10 – 0.25 Greater than <br />or equal to 35 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 25 – 35 <br />0.50 – 0.75 15 – 25 <br />0.75 – 1.00 Less than 15 <br />4 <br />0.25 – 0.50 Greater than <br />or equal to 35 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 />0.50 – 0.75 25 – 35 <br />0.75 – 1.00 15 – 25 <br />1.00 – 1.50 Less than 15 <br />5 <br />0.50 – 0.75 Greater than <br />or equal to 35 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 />0.75 – 1.00 Greater than <br />or equal to 25 <br />1.00 – 1.50 Greater than <br />or equal to 15 <br />Greater than 1.50 Any <br /> <br />265 Sperry, S. and Piltz, S. (2011). The SPIA Index. Retrieved from <br />https://www.weather.gov/media/ffc/iwt2014/IWT2014_Sperry.pdf.