Local mitigation strategy (LMS) - Volusia County Government

SECTION 5: HAZARD PROFILESATMOSPHERIC HAZARDS5.2 HAIL5.2.1 BackgroundHail frequently accompanies thunderstorms and has potential to cause substantial damage. Early in thedevelopmental stages of a hail, ice crystals form within a low-pressure front due to the rapid rising ofwarm air into the upper atmosphere and the subsequent cooling of the air mass. Frozen dropletsgradually accumulate on the ice crystals until they develop sufficient weight to fall as precipitation. Hailprecipitation falls in sphere or irregularly shaped masses greater than 0.75 inches in diameter. The sizeof hailstones is a direct function of the size and severity of the storm. High velocity updraft winds arerequired to keep hail in suspension in thunderclouds. The strength of the updraft is a function of theintensity of heating at the Earth’s surface. Higher temperature gradients relative to elevation above thesurface result in increased suspension time and hailstone size.5.2.2 Location and Spatial ExtentHail is often produced during a thunderstorm event which has no geographic limitations to the area itaffects. Therefore, it is assumed that all of Volusia County is uniformly at risk to a hail event. Impactstypically include downed power lines and trees and damage to vehicles and mobile homes.5.2.3 Historical OccurrencesAccording to the National Climatic Data Center, there have been 106 recorded hail events in VolusiaCounty since 1983, as shown in Table 5.3 1 . Hail has caused a total of $231,092 (2009 dollars) inproperty damage, but has not resulted in any injuries or deaths. Hail sizes for these events rangefrom 1.00 inches to 2.75 inches in diameter. The locations of historically recorded hail events areshown in Figure 5.1. The emergency management officials from the Volusia County jurisdictionsdetermined that only hail that was greater than one inch in diameter was to be listed in Table 5.3.1 A Hail event that affects several jurisdictions on the same day is classified as a single event.Volusia County Multi-jurisdictional Local Mitigation StrategyFebruary 20105:5