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Sherburne County Multi -Hazard Mitigation Plan, 2020 <br />Sherburne County Emergency Management identified that there are existing program gaps and <br />deficiencies that make its citizens more vulnerable to summer storms (includes tornadoes) and should <br />be addressed with new mitigation efforts to reduce vulnerability. They include: <br />Warning Siren Coverage— Sherburne County has a large warning siren system, however, some of the <br />sirens are old and have not been serviced frequently. This could lead to sirens not working properly, <br />causing residents to not receive warnings during an event. Emergency Services is currently working on <br />updating the county's outdoor warning system. Sherburne County has implemented CodeRED, <br />however, not everyone has enrolled in the community notification system. The outdoor warning <br />system seems to be the best method of warning the general public. <br />Backup Power— Not all county and city facilities have backup power in the event of a severe storm that <br />takes out power. <br />Storm Shelters/Community Safe Rooms — There are many areas throughout the county that do not have <br />safe rooms or storm shelters to protect vulnerable populations from severe storm and <br />tornadoes/extreme wind events (i.e., mobile home parks, campgrounds or schools). <br />4.3.2 Windstorms <br />FEMA defines winds in excess of 58 miles per hour, excluding tornadoes, as windstorms. Straight-line <br />winds and windstorms are used interchangeably in the plan. This hazard is treated as a different <br />category than tornadoes (which may also include high winds). Windstorms are among the nation's <br />most severe natural hazards in terms of both lives lost and property damaged. <br />Severe winds can damage and destroy roofs, toss manufactured homes off their pier foundations, and <br />tear light -framed homes apart. There are several different types of windstorms. A "downburst" is <br />defined as a strong downdraft with an outrush of damaging winds on or nearthe earth's surface. <br />Downbursts may have wind gusts up to i3o mph and are capable of the same damage as a medium- <br />sized tornado. A "gust front" is the leading edge of the thunderstorm downdraft air. It is most <br />prominent near the rain -free cloud base and on the leading edge of an approaching thunderstorm and <br />is usually marked by gusty, cool winds and sometimes by blowing dust. The gust front often precedes <br />the thunderstorm precipitation by several minutes. Straight-line winds, when associated with a <br />thunderstorm, are most frequently found with the gust front. These winds originate as downdraft air <br />reaches the ground and rapidly spreads out, becoming strong horizontal flow. <br />When wind speeds are not able to be measured, they are estimated. Part of the process to determine <br />wind speed is observing the damage. Table i8 lists the expected effects of increasing wind speeds. <br />Table 18. <br />26-38 knots Trees in motion. Lightweight loose objects (e.g., lawn furniture) tossed or toppled. <br />(30-44 mph) <br />39-49 knots Large trees bend; twigs, small limbs break; and a few larger dead or weak branches may <br />(45-57 mph) break. Old/weak structures (e.g., sheds, barns) may sustain minor damage (roof, <br />doors). Buildings partially under construction may be damaged. A few loose shingles may be <br />Page145 <br />