SECTION 4: RISK ASSESSMENT
Figure 4.17 – Lightning Flash Density (2008-2017)
Source: Vaisala
Extent Thunderstorm Winds
The magnitude of a thunderstorm event can be defined by the storm’s maximum wind speed and its impacts. NCEI divides wind events into several types including High Wind, Strong Wind, Thunderstorm Wind, Tornado and Hurricane. For this severe weather risk assessment, High Wind, Strong Wind and Thunderstorm Wind data was collected. Hurricane Wind and Tornadoes are addressed as individual hazards. The following definitions come from the NCEI Storm Data Preparation document. High Wind – Sustained non-convective winds of 40mph or greater lasting for one hour or longer or winds (sustained or gusts) of 58 mph for any duration on a widespread or localized basis. Strong Wind – Non-convective winds gusting less than 58 mph, or sustained winds less than 40 mph, resulting in a fatality, injury, or damage. Thunderstorm Wind – Winds, arising from convection (occurring within 30 minutes of lightning being observed or detected), with speeds of at least 58 mph, or winds of any speed (non-severe thunderstorm winds below 58 mph) producing a fatality, injury or damage. The strongest recorded thunderstorm wind event in the county occurred on January 11, 2014 with a measured gust of 86 mph at Raleigh-Durham International Airport and estimated gusts of 75 mph elsewhere across the county. The event caused one fatality, four injuries, and an estimated $1.35 million
in property damage. Impact: 2 – Limited Spatial Extent: 4 – Large
Wake County Multi-Jurisdictional Hazard Mitigation Plan 2019
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