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Ramsey County | Multi-Jurisdiction Hazard Mitigation Plan 72 The summer weather hazards chapter encompasses natural weather hazards most likely to occur in the spring and summer months. The most common types of summer weather hazards experienced in Ramsey County are described below. • Extreme heat: The NWS does not have a set definition for extreme heat but instead calibrates the point at which forecasters warn residents based on the region's climate. For central states, including Minnesota, Heat Advisories are issued when the heat index exceeds 100 degrees. Excessive Heat Warnings are issued when the heat index exceeds 105 degrees. • Heatwave: Heatwaves are periods of abnormally hot weather generally lasting more than two days. Heat waves can occur with or without high humidity. • Hail: Hail forms inside a thunderstorm or other storms with strong updrafts of warm air and downdrafts of cold water. If a water droplet is picked up by the updrafts, it can be carried well above the freezing level. Water droplets freeze when temperatures reach 32 degrees Fahrenheit (°F) or colder. As the frozen droplet begins to fall, it may thaw as it moves into warmer air toward the bottom of the thunderstorm. However, the droplet may be picked up again by another updraft and carried back into the cold air and refreeze. With each trip above and below the freezing level, the frozen droplet adds another layer of ice. The frozen droplet, with many layers of ice, falls to the ground as hail. Most hail is small and typically less than two inches in diameter. • Lightning: Lightning is a bright flash of electrical energy produced by a thunderstorm. All thunderstorms produce lightning and are very dangerous. Lightning ranks as one of the top weather killers in the U.S., where an average of 300 people are injured and 80 are killed each year. Lightning can occur anywhere there is a thunderstorm, often strikes outside the heavy rain in a thunderstorm, and may occur as far as 10 miles away from any rainfall. Note that a single summer weather event may include one or more of these hazards. 3.11.2 LOCATION All communities within Ramsey County are vulnerable to summer weather. 3.11.3 EXTENT 3.11.3.1 Extreme Heat and Heatwaves Each NWS Forecast Office issues heat-related alerts as needed. Local offices often work with partners to decide when to issue an alert for a specific area. The Heat Index is a measure of how hot it feels when factoring in the relative humidity at a given location. This can be used as a decision-making tool when issuing heat-related products. The Heat Index is provided as Figure 12.