Exponential spectra are found to characterize variability of the Northern Annular Mode (NAM) for periods less than 36 days. This corresponds to the observed rounding of the autocorrelation function at lags of a few days. The character-istic persistence timescales during winter and summer is found to be ∼5 days for these high frequencies. Beyond per-iods of 36 days the characteristic decorrelation timescale is ∼20 days during winter and ∼6 days in summer. We con-clude that the NAM cannot be described by autoregressive models for high frequencies; the spectra are more consistent with low‐order chaos. We also propose that the NAM exhibits regime behaviour, however the nature of this has yet to be identified.