Already this summer, the eastern US has experienced dangerously hot weather. Just this week, nearly 160 million citizens were under some kind of heat alert Tuesday.
The Center for Disease Control and Prevention is the government agency that keeps track of heat related deaths and illnesses, and the numbers are rising. In 2022, there were 1,714 deaths, the highest in over 20 years.
Each local National Weather Service office issues 3 different heat alerts to classify the appropriate level of risk posed by the heat. Just like for tornadoes and severe thunderstorms, the NWS issues both extreme heat warnings and extreme heat watches. An extreme heat warning is issued when extremely dangerous heat is happening or is expected to happen. When there is an extreme heat warning, it’s recommended that you avoid strenuous outdoor activities if possible and to drink extra water and take frequent breaks if you must work outside. This is the highest level heat alert, and it’s recommended that you check on family and neighbors, especially if they are elderly or do not have adequate air conditioning.
When the details about upcoming heat are less certain, the National Weather Service may issue a heat watch. A heat watch is issued before the heat arrives, and is purpose is to give residents an opportunity to make alternate plans to avoid the heat. When confidence of upcoming dangerous heat increases, the excessive heat warning will be upgraded to an excessive heat warning.
The last heat alert is a heat advisory. This is the lowest level heat alert, it’s issued when dangerous heat is happening, but the heat is not quite to the level of an excessive heat warning. Heat alert thresholds do vary a bit from place to place, as people living in cooler climates will have impacts from heat at lower temperatures that someone who lives in a hotter climate and is more accustomed to the heat.
In the cooler regions of South Carolina, the heat alert thresholds are not as high. Areas of the Upstate and into the Pee Dee are typically a little less hot than other areas of the state, and here, heat advisories are issued when the heat index is greater than 105 degrees for two hours. The higher level Excessive Heat Warning is issued when the heat index values reach 100 degrees for two consecutive hours.
The typically warmer areas of the state have slightly higher heat alert criteria. In the lowcountry and midlands, a the lower level heat advisory is issued when the heat index climbs to 108 degrees or greater to two hours. When the heat index rises to 113 degrees or greater, the higher level excessive heat warning will be issued.