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2021 Multijurisdictional Local Hazard Mitigation Plan 14.2 HAZARD PROFILE 14.2.1 Past Events Appendix F lists past severe weather events in San Mateo County as recorded by NOAA since 1950. Table 14-3 summarizes those for which deaths, injuries, or property damage were reported or a federal disaster declaration was issued. 14.2.2 Location Severe weather events have the potential to happen anywhere in San Mateo County. Communities in low-lying areas next to streams or lakes are more susceptible to flooding. Regions near San Francisco Bay are more li kely to experience fog. Wind events are most damaging to areas that are heavily wooded. PSPS events can occur anywhere that relies on electrical power from an outside source. There is no clearly defined extent and location mapping available for atmospheric rivers, fog, or tornado. The extent discussion for these hazards is addressed under in Section 14.2.4 (Severity). Extreme Heat Climate Ready San Mateo County has created an interactive tool that includes climate scenarios for extreme heat, showing average temperatures and average number of high heat days per year across the county (County of San Mateo Office of Sustainability, 2021). The countywide temperature distribution for a base year (1995) is shown in Figure 14-3. Highest temperatures are found in the urban lowlands along the south Bay shore and in an area extending southeast from the coastline between Pescadero and San Gregorio. Temperatures are cooler along the mountain ridge extending northwest to southeast across the center of the county. Windstorms All of San Mateo County is subject to high winds from thunderstorms, tornadoes, and other severe weather events. According to the FEMA Winds Zones of the United States map (Figure 14-4), San Mateo County is located in Wind Zone I, where wind speeds can reach up to 130 mph. The map indicates the strength of windstorms in the United States, and the general location of the most wind activity. This is based on 40 years of tornado data and 100 years of hurricane data, collected by FEMA. Tornadoes Tornadoes have been documented in every state in the United States, and on every continent with the exception of Antarctica. Approximately 1,200 tornadoes occur in the United States each year, with the central portion of the country experiencing the most. Tornadoes can occur at any time of the year, with peak seasons at different times for different states (National Severe Storms Laboratory, 2018). As noted earlier, the State of California and San Mateo County have a lower risk for tornados than elsewhere in the country. Tornado risk within the County is fairly equal across the region; historical tornado events have been documented on both the bayside and coastal region of the County. Community members near the Pacific Ocean or the San Francisco Bay (as opposed to the central area of the County) may be at a slightly higher risk for tornados; however, historical data is not sufficiently exhaustive enough to confirm this potential trend. Tornadoes are usually localized; however, severe thunderstorms can result in conditions favorable to the formation of numerous or long-lived tornadoes. 14-8