The blistering heat wave that persisted across much of the central and eastern United States from mid to late July made July 2006 the second hottest since records began in 1895 (1936 was the hottest).

More than 50 new high temperature records were established in the central and western U.S. during this month. These unusually high temperatures had adverse effects on health and endangered lives. In California alone during the heat wave more than 150 deaths were believed to have been heat-related. NOAA's National Weather Service (NWS) collaborates with public and private sector organizations, academia, the medical community, and the media to create and deliver new and enhanced health weather products and services. Among these services is the provision of forecasts and warnings for excessive heat. Excessive heat accounts for more deaths annually than the combined number of deaths from tornadoes, hurricanes, lighting, and flash floods. The NWS currently issues a suite of excessive heat products to provide the Nation advance notice of excessive heat events. These products are based on a single heat index value derived from temperature and humidity. To provide additional support to NWS forecasters, NOAA has supported development of the Heat Health Watch/ Warning Systems (HHWS). These HHWS, developed by Dr. Laurence Kalkstein of the University of Miami and others, provides customized excessive heat guidance for specific urban areas based on local climatology and meteorology, human health response to excessive heat, and urban structure and demographics. The Heat Health Watch/Warning System expands upon the Heat Index in that it considers much more than temperature and is based on actual weather-health relationships.

The NOAA's NWS is now in the process of developing these locally-specific HHWS for cities across the country to provide enhanced guidance information for forecasting extreme heat events. There are currently 17 HHWS in operation, covering 26 U.S. cities with population exceeding 500,000. While the NOAA NWS still uses the heat index as its official guidance for issuing excessive heat watches, warnings and advisories in most areas, the HHWS is now being used as guidance for these 26 large cities.