Longest Stretch of High Heat Days
An interactive data tool showing how the number of consecutive high heat days is projected to change in the future.
Historical Changes in the Heat Index
Historical Changes in the Heat Index
This tool is excerpted from Mid-Atlantic Regional Climate Impacts Summary and Outlook: Fall 2023.
Tool Background
The Heat Index is a combined measure of temperature and humidity that reflects how hot it feels to individuals. High Heat Index values can be dangerous to human health and serve as an important metric for setting policies or regulations that reduce exposure and protect public health. Table 1 shows four classifications of the Heat Index that represent levels at which human health can be impacted.
Table 1. Heat Index Classifications
| Classificiation | Heat Index | Effect on the Body |
|---|---|---|
| Caution | 80°F–90°F | Fatigue possible with prolonged exposure and/or physical activity |
| Extreme Caution | 90°F–103°F | Heat stroke, heat cramps, or heat exhaustion possible with prolonged exposure and/or physical activity |
| Danger | 103°F–124°F | Heat cramps or heat exhaustion likely, and heat stroke possible with prolonged esposure and/or physical activity |
| Extreme Danger | 125°F or higher | Heat stroke highly likely |
Source: National Weather Service
Key Findings
- The Mid-Atlantic region has seen two to thee times more days with heat index values above the Caution classification, when human health may be impacted with prolonged exposure, compared to 1981–1990.
- The region has also seen three to five times more days with heat index values above the Extreme Caution classification, at which heat stroke, heat cramps and heat exhaustion are possible.
- Much of Virginia has regularly experienced more than 100 days per year above the Extreme Caution classification, at which heat stroke, heat cramps and heat exhaustion are possible.
Figure 1. Days with High Heat Index Values
How to Use the Tool
Selecting Temperature Thresholds and Time Periods Use the filters to the right of the maps to adjust the Heat Index threshold and the 10-year time period.
Technical Notes
Heat Index values were calculated based on station data for air temperature and relative humidity using the Rothfusz equation employed by the National Weather Service.1
Footnotes
https://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml Return to text ⤴