AR(1) models are commonly employed to model time series, and the "same-as-yesterday" model is the case where the AR1 coefficient equals 1. There is is some mean

AR(1) models are commonly employed to model time series, and the "same-as-yesterday" model is the case where the AR1 coefficient equals 1. There is is some mean reversion in seasonally-adjusted temperature, so an AR1 coefficient less than 1 should work better.