Wildfire seasons are lengthening and intensifying in America. The western U.S. has experienced a strong increase in the average annual number of fire weather days since 1973. These results are consistent with findings from previously published research.

Fire weather refers to meteorological conditions that promote the spread of wildfires. As fire weather becomes more prevalent, there are more days when extreme conditions can turn small blazes into big ones or fuel the growth of large wildfires.

Areas in Southern California, New Mexico, Texas, and Arizona have experienced some of the largest increases in annual fire weather days, with some areas now seeing around two more months of fire weather per year compared to a half century ago. Some places, including parts of California, Nevada, New Mexico, and Texas now experience fire weather around twice as often as in the early 1970s.

This analysis uses data from 476 weather stations to assess fire weather trends in 245 climate divisions spanning the contiguous U.S. from 1973 to 2024.