National Temperature, Humidity & Heat Index

National Temperature

          About this map:
          Both high and low temperature extremes can be harmful to humans and animals. Use this map to take the proper 
          precautions when extreme conditions exist or appear to be approaching your local area.
National Heat Index

          About this map:
          The Heat Index is a measure of relative discomfort due to combined heat and high humidity. It was developed by 
          R.G. Steadman (1979) and is based on physiological studies of evaporative skin cooling for various combinations of
          ambient temperature and humidity. As temperatures climb above 90 °F and humidity goes above 40 percent, 
          conditions are ripe for heat-related illnesses. 
          Use this map to determine when possible dangers exist due to the heat index.
National Relative Humidity

          About this map:
          Humidity or relative humidity measures the amount of water vapor in the air relative to the temperature. It is 
          important in weather because humidity affects how humans feel. A hot, humid day feels hotter because we cannot 
          sweat as effectively. A cool, dry day feels colder because moisure evaporates more easily. Use this map to 
          determine relative humidity trends across the nation.

Weather Fast Fact
Excessive Heat Watch:
This is issued by your local NWS Forecast Office when it is possible for the heat index to exceed 115 degrees for any length of time during the day or the heat index will be equal to or exceed 105 degrees for more than 3 hours in a day for at least 2 consecutive days.