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2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br />4.6.10. Winter Weather <br />4.6.10.1. Description <br />For the purposes of this Plan, winter weather includes ice storms, heavy snow, and blizzards. Each <br />hazard is examined independently, but it is recognized that these could occur simultaneously. Refer to <br />the severe weather section of this Plan for further details on cold wave/extreme cold. <br />Winter weather consists of winter storm events in which the main type of precipitation is snow, sleet, <br />and/or freezing rain'257 Table 4-149 provides a description for each of the three (3) types of winter <br />precipitation. 258 <br />Table 4-149. Winter Precipitation Types <br />A winter storm requires three (3) basic ingredients - cold air, lift, and moisture. Cold air that is below <br />freezing (less than 32'F) must be present in the clouds and near the ground to make snow and/or ice. <br />Lift is needed to raise moist airto form the clouds and cause precipitation. For example, warm air colliding <br />with cold air is forced to rise over the cold dome; the boundary between warm and cold air masses is <br />called a front. Finally, moisture is needed to form clouds and precipitation. A source of moisture can be <br />air blowing across of body of water (e.g., large lake, ocean).-2se <br />lce Storm <br />An ice storm is a storm which results in the accumulation of at least 0.25 inches of ice on exposed <br />surfaces (i.e., a significant accumulation of freezing rain lasting several hours or more). These storms <br />create extremely hazardous driving and walking conditions. Additionally, the accumulation of ice on trees, <br />257 Federal Emergency Management Agency. (2023). Winter Weather. Retrieved from <br />https ://haza rds.fem a. qov/n ri/wi nter-weather. <br />258 National Oceanic and Atmospheric Administration, National Severe Storms Laboratory. (n.d.). Severe Weather <br />101 : Types of Winter Weather. Retrieved from https://www.nssl.noaa.qov/education/svrwx101/winteritvpes/. <br />25e National Oceanic and Atmospheric Administration, National Severe Storms Laboratory. (n.d.). Severe Weather <br />101: Winter Weather Basics. Retrieved from https://www.nssl.noaa.qov/education/svrwx10'1/winter/. <br />Snow <br />Most of the precipitation that falls in the wintertime begins as snow because the top <br />layer of the storm is usually cold enough to create snowflakes. Snowflakes are a <br />collection of ice crystals that cling to each other as they fall towards the ground. <br />Precipitation continues to fall as snow when the temperature remains at or below <br />32'F from the cloud base to the oround. <br />Sleet <br />Occurs when snowflakes only partially melt when they fall through a shallow layer of <br />warm air. These slushy drops refreeze as they then fall through a deep layer of <br />freezing air above the surface, and eventually reach the ground as frozen rain drops <br />that bounce on impact. <br />Freezing Rain <br />Occurs when snowflakes descend into a warmer layer of air and melt completely. <br />When these liquid water drops fall through another thin layer of freezing air just above <br />the surface, they do not have enough time to refreeze before reaching the ground. <br />Because they are "supercooled," they instantly refreeze upon contact with anything <br />that is at or below 32'F, creating a glaze of ice on the ground, trees, power lines, or <br />other obiects. <br />DefinitionType <br />Chapter 4: Hazard ldentification and Risk Assessment 197