What is it?
How often and how severely a county is exposed to dangerously hot temperatures. Often measured as days per year above a heat-index threshold (e.g., 95°F or 100°F).
Why it matters
Extreme heat is the leading weather-related cause of death in the U.S. It triggers heart attacks, strokes, kidney failure, and worsens chronic conditions. Elderly residents, outdoor workers, and people without air conditioning are at highest risk.
Reference value
Counties with more than 30 days per year above a heat index of 95°F, combined with a high share of elderly or low-AC-access residents, are higher concern.
Related health outcomes
- Heart attack
- Stroke
- Kidney injury
- Heat exhaustion mortality
Data source
NOAA NCEI climate data · View source →