Wake County Hazard Mitigation Plan - January 2020


individuals are susceptible if they participate in strenuous physical activities during hot weather or are not acclimated to hot weather. Table 4.29 lists typical symptoms and health impacts of exposure to extreme heat. Table 4.29 – Typical Health Impacts of Extreme Heat

Heat Index (HI) Disorder 80-90° F (HI)

Fatigue possible with prolonged exposure and/or physical activity

90-105° F (HI)

Sunstroke, heat cramps, and heat exhaustion possible with prolonged exposure and/or physical activity

105-130° F (HI) Heatstroke/sunstroke highly likely with continued exposure Source: National Weather Service Heat Index Program, www.weather.gov/os/heat/index.shtml

The National Weather Service has a system in place to initiate alert procedures (advisories or warnings) when the Heat Index is expected to have a significant impact on public safety. The expected severity of the heat determines whether advisories or warnings are issued. A common guideline for issuing excessive heat alerts is when the maximum daytime Heat Index is expected to equal or exceed 105 degrees Fahrenheit (°F) and the night time minimum Heat Index is 80°F or above for two or more consecutive days. A heat advisory is issued when temperatures reach 105 degrees and a warning is issued at 115 degrees. Impacts of extreme heat are not only focused on human health, as prolonged heat exposure can have devastating impacts on infrastructure as well. Prolonged high heat exposure increases the risk of pavement deterioration, as well as railroad warping or buckling. High heat also puts a strain on energy systems and consumption, as air conditioners are run at a higher rate and for longer; extreme heat can

also reduce transmission capacity over electric systems. Warning Time: 1 – More than 24 hours warning time Duration: 4 – More than one week

Location The entire planning area is susceptible to high temperatures and incidents of extreme heat.

Extent The extent of extreme heat can be defined by the maximum apparent temperature reached. Apparent temperature is a function of ambient air temperature and relative humidity and is reported as the heat index. The National Weather Service Forecast Office in Raleigh sets the following criteria for heat advisory and excessive heat warning:  Heat Advisory – Heat Index of 105°F to 109°F for 3 hours or more. Can also be issued for lower values 100ºF to 104ºF for heat lasting several consecutive days  Excessive Heat Watch – Potential for heat index values of 110°F or hotter within 24 to 48 hours. Also issued during prolonged heat waves when the heat index is near 110°F  Excessive Heat Warning – Heat Index of 110°F or greater for any duration Based on data from the “Raleigh State Univ” weather station from January 1892 through January 2019, the highest temperature recorded in Wake County was 107°F and occurred in July 2011. Impact: 3 – Critical Spatial Extent: 4 – Large

Wake County Multi-Jurisdictional Hazard Mitigation Plan 2019


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