SECTION 4: RISK ASSESSMENT
March 6, 2011 – a weak EF-0 tornado touched down just northeast of downtown Rolesville along NC Highway 401 (Main Street). The tornado tracked to the northeast for two miles, causing damage to trees, homes and other infrastructure, resulting in $100,000 in property damage. An elderly man was injured from the tornado due to a house fire. April 16, 2011 – A strong storm system produced nine tornadoes in the Raleigh CWA, including two EF3s and four EF2s. The tornadoes left eight dead with approximately 275 injuries. In Burt, an EF0 tornado entered southwest Wake County and tracked northeast, causing tree, roof and infrastructure damage. In total, 2,270 homes were damaged, including 67 homes that were destroyed and 184 homes that suffered major damage; additionally, 34 businesses were damaged. NCEI recorded four fatalities in a trailer park, 67 injuries and $115 million in property damage. November 28, 1988 – A powerful tornado touched down in Umstead State Park in the northwest part of Raleigh, three miles southeast of the center of Raleigh-Durham Airport. The tornado tracked across one of the most densely populated parts of the City of Raleigh, destroying hundreds of homes and damaging thousands of others. Two people were killed in Raleigh. The strongest damage, mostly F3 with some very weak F4, occurred along a 4 mile long portion of the path extending northeast from where it crossed U.S. Highway 70, four miles east of Raleigh Airport. Numerous businesses along U.S. Highway 70 were destroyed, including a K-mart. The tornado destroyed a total of 426 residences and 78 businesses. It damaged 2,057 residences, leaving 978 people homeless. Four people were killed and 154 were injured; total damage was near $77.2 million. The track of the tornado was almost continuous for 83 miles. Outside of the above time period, NCEI also records an F2 tornado on November 2, 1966 that caused nine injuries and $250,000 in damage. November 2, 1966 – In the area east and south of Raleigh, two homes and five house trailers were destroyed, three trailers and six homes severely damaged, and minor damage to approximately twenty other homes and business buildings, with trees twisted off and power poles broken. Probability of Future Occurrence Probability of future occurrence was calculated based on past occurrences and was assumed to be uniform across the county. In a thirty-year span between 1988 and 2017, Wake County experienced 19 separate tornado incidents over 15 separate days. This correlates to a 63 percent annual probability that the county will experience a tornado somewhere in its boundaries. Only three of these past tornado events was a magnitude EF2 or greater; therefore, the annual probability of a significant tornado event is approximately 10 percent. Probability: 3 – Likely Climate Change There presently is not enough data or research to quantify the magnitude of change that climate change may have related to tornado frequency and intensity. NASA’s Ea rth Observatory has conducted studies which aim to understand the interaction between climate change and tornadoes. Based on these studies meteorologists are unsure why some thunderstorms generate tornadoes and others don’t, beyond knowing that they require a certain type of wind shear. Tornadoes spawn from approximately one percent of thunderstorms, usually supercell thunderstorms that are in a wind shear environment that promotes rotation. Some studies show a potential for a decrease in wind shear in mid-latitude areas. Because of uncertainty with the influence of climate change on tornadoes, future updates to the mitigation plan
Wake County Multi-Jurisdictional Hazard Mitigation Plan 2019
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