We propose a model for non-stationary spatiotemporal data. To account for s
patial variability, we model the mean function at each time period as a loc
ally weighted mixture of linear regressions. To incorporate temporal variat
ion, we allow the regression coefficients to change through time, The model
is cast In a Gaussian state space framework, which allows us to include te
mporal components such as trends, seasonal effects and autoregressions, and
permits a fast implementation and full probabilistic inference for the par
ameters, interpolations and forecasts. To illustrate the model, we apply it
to two large environmental data sets: tropical rainfall levels and Atlanti
c Ocean temperatures.