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Sherburne County Multi -Hazard Mitigation Plan, 2020 To determine the probability of future tornado events in Sherburne County, all past observed tornado events and the period in which they occurred were examined. Based on records in the NCEI Storm Events Database through May of 203.9, the relative frequency of tornado events in the County is .04 events per year. This relative frequency can be used to inferthe probability of these events occurring in the future. Tornadoes and Climate Change Tornadoes and other severe thunderstorm phenomena frequently cause as much annual property damage in the U.S. as do hurricanes, and often cause more deaths. Although recent research has yielded insights into the connections between global warming and the factors that cause tornados and severe thunderstorms, such as atmospheric instability and increases in wind speed with altitude (Del Genio, Yao, & Jonas, 2007), these relationships remain mostly unexplored, largely because of the challenges in observing thunderstorms and tornadoes and simulating them with computer models (National Climate Assessment Development Advisory Committee, 2013). According to Harold Brooks of NOAA's National Severe Weather Laboratory, there is increasing variability in the "start" of tornado season. The number of days with more than 3o EF1 or greater tornadoes is increasing, while the number of days with at least one EFi or greater tornadoes is decreasing. Thus, tornadoes are occurring on fewer days, but more are occurring on outbreak days. The earliest reported tornado in Minnesota occurred on March 6, 2017, when two tornadoes touched down in southern Minnesota, which was 12 days earlier than the previous record. The Zimmerman tornado occurred 3.3.5 miles further north than the previous record from 1.968. According to State Meteorologist Paul Huttner, "Those records fit seasonally and geographically with longerterm climate trends pushing weather events earlier in the season and further northward" (Huttner, MPR News, 2017) The state of Wisconsin has recorded three tornadoes in January and six in December during the period of 3.$44-20i3 (National Weather Service Weather Forecast Office, 203-4), including a January tornado in 2008. Vulnerability The likelihood of a tornado does not vary geographically in Sherburne County. However, certain populations may be more vulnerable and less resilient to the impacts of a tornado. Because communication is so important before a tornadic event, citizens that are living in rural areas, have limited mobility, do not live near an outdoor warning siren or do not use social media may be more affected. According to the Social Vulnerability Index results in Figure 4, citizens with social factors that make up the household composition and disability theme may be greatest in the area west of Elk River. As with all summer storms, those who work outdoors or do not have permanent housing are also at greater risk. People living in mobile home parks are particularly vulnerable to tornadoes. While Minnesota law requires most mobile home parks to have storm shelters, many do not (Sepic, 2017). There are four mobile home parks in Sherburne County (see Figure A - 3.3). Page144