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2021 Multijurisdictional Local Hazard Mitigation Plan brownouts or power loss due to impact on local infrastructure – such as the increased demand for air conditioning, rolling blackouts and PSPS events. Extreme heat events may degrade the quality of roadways and railways, resulting in closures and travel delays. Extreme heat events are among the deadliest weather hazards facing communities. They are the primary weather-related cause of death in the United States. In a 10-year record of weather fatalities across the nation (2006 – 2015), excessive heat claimed more lives each year than floods, lightning, tornadoes, and hurricanes. According to the California Climate Adaptation Strategy, heat waves have claimed more lives in California than all other declared disaster events combined. Older adults, children, and sick or overweight individuals are at greater risk from extreme heat. 14.1.3 Fog Fog is a cloud near the ground. Fog forms when air close to the ground can no longer hold all the moisture it contains. This occurs either when air is cooled to its dew point or the amount of moisture in the air increases. Heavy fog is particularly hazardous because it can restrict surface visibility. Severe fog incidents can close roads, cause vehicle accidents and airport delays, and impair the effectiveness of emergency response. Financial losses associated with transportation delays caused by fog have not been calculated in the United States, but it is known to be substantial. Fog can occur almost anywhere during any season and is classified based on how it forms, which is related to where it forms. Certain seasons are more likely to have foggy days or nights based on a number of factors, including topography. Fog in the Bay Area has different origins depending on the time of year. In the summer, the area is characterized by cool marine air and persistent coastal stratus and fog. In winter, ground fog forms in the moist regions of the Sacramento River Delta and arrives to the region via Suisun and San Pablo Bays and San Francisco Bays on cool easterly drainage winds. While this type of fog is less frequent than summer fogs, it is typically denser and more likely to lead to significantly reduced visibility (Golden Gate Weather Services, 2009). Although fog seems like a minor hazard, it can have significant impacts. The California Highway Patrol (CHP) alone has records of at least four officers whose deaths were indirectly caused by or exacerbated by dense fog and poor visibility (California Highway Patrol, 2021). 14.1.4 Public Safety Power Shutoff Some combinations of weather conditions—particularly high winds, extreme heat, and low humidity—pose increased risks of wildfire. In 2012, the California Public Utilities Commission ruled that California Public Utilities Code gives electric utilities authority to shut off electric power to protect public safety, since power supply systems have the potential ignite wildfires (California Public Utilities Commission 2021). Such shutoffs are referred to as public safety power shutoff events. Given the long, connected nature of power supply systems, a 14-2 Extreme Heat Terminology  Extreme Heat: A period of high heat and humidity with temperatures above 90 ºF for at least two to three days.  High-Heat Days: Days when temperatures exceed 100 °F.  Heat Wave: Five consecutive days when temperatures exceed 100 °F.  Cooling Degree Days: Every degree that the mean daily temperature is above 65 °F. This value is an indicator of how much energy must be expended to keep facilities at a comfortable temperature  Urban Heat Island: Areas that typically lack vegetation (e.g., trees) and have dark, paved surfaces (e.g., parking lots) that absorb more heat and retain it for longer than adjacent, greener areas.