How The National Weather Service Alerts You of Heat Danger

The NWS will initiate alert procedures (advisories or warnings) when the Heat Index (HI) 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 the issuance of excessive heat alerts is when the maximum daytime HI is expected to equal or exceed 105°F and a nighttime minimum HI of 80°F or above for two or more consecutive days.  Some regions and municipalities are more sensitive to excessive heat than others.  As a result, alert thresholds may vary substantially from these guidelines.  Excessive heat alert thresholds are being tailored at major metropolitan centers based on research results that link unusual amounts of heat-related deaths to city-specific meteorological conditions.

The alert procedures are:  

  • Include HI values in zone and city forecasts.
  • Issue Special Weather Statements and/or Public Information Statements presenting a detailed discussion of (1) the extent of the hazard including HI values, (2) who is most at risk, (3) safety rules for reducing the risk.
  • Assist state and local health officials in preparing Civil Emergency Messages in severe heat waves.  Meteorological information from Special Weather Statements will be included as well as more detailed medical information, advice, and names and telephone numbers of health officials.
  • Release to the media and over NOAA's own Weather Radio all of the above information.


What is the Heat Index?
How do we alert you of dangerous temperatures?
How does my body handle the heat?
Why cities make the problems worse
Heat Disorders and Symptoms
How to protect yourself