National Weather Service United States Department of Commerce

HEAT INDEX - what the temperature feels like to the human body based on both the air temperature and humidity.
 

HUMIDITY - the measured amount of moisture in the air.
 

EXCESSIVE HEAT WATCH - issued by your local NWS Forecast Office when it is possible for the heat index to be at or above 105 degrees for two or more hours.
 

EXCESSIVE HEAT WARNING- issued by your local NWS Forecast Office when the heat index is expected to be at or above 105 degrees for two or more hours.
 

HEAT ADVISORY - issued by your local NWS Forecast Office when the heat index is expected to range between 100 to 104 degrees for two or more hours.
 

AIR QUALITY ALERT - is issued by individual states and your local NWS Forecast Office relays the information via an AQA product.