SECTION 4: RISK ASSESSMENT
antidepressants, sleeping pills, or drugs for Parkinson’s disease. However, even young and healthy individuals are susceptible if they participate in strenuous physical activities during hot weather or are not acclimated to hot weather. Table 4.34 lists typical symptoms and health impacts of exposure to extreme heat. Table 4.34 – Typical Health Impacts of Extreme Heat Classification Heat Index (HI) Effect on the body Caution 80-90° F Fatigue possible with prolonged exposure and/or physical activity
Extreme Caution Danger
90-103° F
Heat Stroke, heat cramps, or heat exhaustion possible with prolonged exposure and/or physical activity Heat cramps or heat exhaustion likely, and heat stroke possible with prolonged exposure and/or physical activity
103-124° F
Extreme Danger
125° F or higher
Heat stroke highly likely
Source: National Weather Service
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 2 hours or more and/or excessive heat for 3 consecutive days. • Excessive Heat Watch – Conditions are favorable for an excessive heat event to meet or exceed local Excessive Heat Warning criteria; valid for the entire heat episode and not just the daytime hours.
Note: Excessive heat occurs from a combination of hot temperatures and high humidity.
Wake County, NC Multi-Jurisdictional Hazard Mitigation Plan
WSP June 2024 Page 120
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