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Variability in the start, end, and length of frost‐free periods across the conterminous United States during the past century

The timing of last spring frost dates (LSFDs), first fall frost dates (FFFDs), and frost‐free period lengths (FFPLs) constrains freeze–thaw processes in hydrology, paces the annual life cycles of plants and animals, affects human food production, and influences land–atmosphere interactions, including the water and carbon cycles. Daily minimum temperature data for the conterminous United States (CONUS) from the Global Historical Climatology Network for the 1920–2012 period are used to determine LSFDs, FFFDs, and FFPLs. Analyses of trends and variability in these growing season components indicate a trend towards earlier LSFDs, later FFFDs, and longer FFPLs for most locations in the CONUS. A general change to earlier LSFDs appears to have occurred after about 1983, whereas a change to later FFFDs is most noticeable after about 1993. Comparisons of time series of LSFDs and FFFDs with well‐known climate indices indicate only weak correlations for most sites.