The NWS and CDC worked together to make new “excessive heat risk” maps, adding magenta in April of 2024: When Red-Hot Isn’t Enough: New Government Heat Risk Tool Sets Magenta as Most Dangerous Level (usnews.com)
The old system was based on temperature and had fewer colors on the maps.
The new system is based on the heat index and is based on both temperature and humidity: Heat Forecast Tools (weather.gov)
NWS/NOAA press release: NWS HeatRisk (noaa.gov)
Today’s “heat index”, which looks like a temperature (e.g. 110 degrees) is not the same as a temperature record from years past. Due to high humidity, the temperatures shown on many weather maps, including television and newspapers in 2024, feature the “heat index” rather than temperature, which makes things appear hotter than you probably remembered from, like, last year.
Last year, the news media also got in to publishing “pavement temperatures” – a metric no one had heard of until the past few years. But guaranteed, in summer, to produce scary high temperature readings: Media lying about pavement temperature and pavement burns in Phoenix – Coldstreams
