By estimating trends in time-varying percentiles of daily air temperature across North America, variations in the entirety of the air-temperature frequency distribution are evaluated. Strong warming (2-3C/50yr) of daily maximum temperatures from 1948 to 2000 has been restricted to December to April in northwestern North America, but has occurred across all percentiles. More-intense warming (>3C/50yr) in daily minimum temperatures has been more widespread – occurring over the western half of North America – but has been concentrated in the lower portion of the air-temperature frequency distribution during January to March. The coldest minimum temperatures, therefore, are warming at a faster rate than the warmest minimum temperatures.