1. A computer-readable storage medium storing a program that, when executed by a processor, causes the processor to: select a reference set of profiles from previous periods; estimate model parameters of a time series based on the reference set, wherein the model parameters comprise a first variance for a hidden noise source; calculate a probability density function for the time series including determining a second variance for the probability density function based at least in part on the first variance for the hidden noise source; and generate a forecast from the probability density function.