As the setup of such a text forecasting task is essentially similar to summarizing future text data, we use two popular evaluation metrics from the literature of text summarization, i.e., BLEU (Papineni et al., 2002) and ROUGE (Lin, 2004), where a score is generated by comparing the automatically generated text against some reference text written by humans.
neither BLEU nor ROUGE considers the notion of time, thus we need a time-sensitive customization of both BLEU and ROUGE.