>As with the 2012 map, the new version has 13 zones across the United States and its territories. Each zone is broken into half zones, designated as “A” and “B.” For example, zone 7 is divided into 7a and 7b half zones. When compared to the 2012 map, the 2023 version reveals that about half of the country shifted to the next warmer half zone, and the other half of the country remained in the same half zone. That shift to the next warmer half zone means those areas warmed somewhere in the range of 0-5 degrees Fahrenheit; however, some locations experienced warming in the range of 0-5 degrees Fahrenheit without moving to another half zone.
>These national differences in zonal boundaries are mostly a result of incorporating temperature data from a more recent time period. The 2023 map includes data measured at weather stations from 1991 to 2020. Notably, the 2023 map for Alaska is “warmer” than the 2012 version. That’s mainly because the new map uses more data representing the state’s mountain regions where, during winter, warm air overlies cold air that settles into low-elevation valleys, creating warmer temperatures.