b'SEVERE WEATHERA severe storm is an atmospheric disturbance thatThunderstormsresults in one or more of the following phenomena:A thunderstorm is a rain event that includes thunder strong winds, large hail, thunderstorms, tornadoes,and lightning. A thunderstorm is classied as severe rain, snow, or other mixed precipitation (see Figure 7 when it contains one or more of the following: hail with for historic distribution of severe storms throughoutat least a one-inch diameter, winds gusting more than Idaho). Of the 47 Presidential Disaster declarations in50 knots (58 mph), or tornado. Typical thunderstorms Idaho since 1954, ten have been attributed to includeare 15 miles in diameter and last an average of 30 storms or severe storms.2 minutes. An estimated 100,000 thunderstorms occur each year in the United States, with approximately 10 Winter Storms percent of them classied as severe.2Winter storms, which are generally characterized by low temperatures and blowing snow, range widelyLightningin size, duration, and intensity. These storms mayAccording to the National Weather Service, lightning impact a single community or a multi-state areais a visible electrical discharge produced by a and may last hours or days. A severe winter stormthunderstorm. The discharge can occur within or is dened as one that drops four or more inches ofbetween clouds, between the cloud and air, between snow during a 12-hour period, or six or more inchesa cloud and the ground, or between the ground during a 24-hour span. A blizzard is a winter stormand a cloud. A lightning discharge may be over ve with winds exceeding 35 miles per hour accompaniedmiles in length, generate temperatures over 50,000F, by blowing snow and reduced visibility. An ice stormand carry 50,000 volts of electrical potential. In the occurs when damaging accumulations of ice areUnited States, an average of 300 people are injured expected during freezing rain situations, and whenand 80 people are killed by lightning each year. Based cold rain freezes immediately on contact with theon National Lightning Detection Network data, the ground, structures, and vegetation, potentially pullingState of Idaho received up to three cloud-to-ground down trees and utility lines resulting in loss of powerlightning ashes per square mile from 2007 to 2016.2and communication. Past winter storm disasters have been focused in the western and northern portionsHailof Idaho, but severe winter storms are possibleHail is typically associated with thunderstorms. The throughout the state.2 National Weather Service denes hail as showery precipitation in the form of irregular pellets or balls of ice more than ve millimeters in diameter, falling from a cumulonimbus cloud. Hail is a product of thunderstorms and their dynamic internal winds. Hail forms inside a thunderstorm where there are strong updrafts of warm air and downdrafts of cold water. Water droplets turn to ice by cycling in and out of altitudes where freezing occurs until the ice becomes heavy enough to fall to the earth as hail. Thunderstorms are classied as severe when hail reaches a diameter of one-inch or greater.2106 I D A H O I N F R A S T R U C T U R E G U I D E B O O K'