Objective Winter Temperature Forecasts: An Update and Extension to the Western United States

Abstract

This study expands on previous studies (Harnack and Landsberg, 1978; Harnack, 1979) in that objective, statistical winter temperature forecast models are tested and verified for three additional winters (1979?81); models have been formulated and tested for the first time for the western one-third of the United States; new models have been formulated and tested using predictors defined for October; and Northern Hemisphere sea level pressure (SLP) has been tested as a predictor. An independent sample was used to test regression models. The main results include: 1) Among the ?November? type predictor models, the sea surface temperature (SST) only model continues to be superior to the others when tested on independent data, including those models using circulation predictors, and it performs significantly better than chance expectation. 2) The SST-only model performed much better in the eastern two-thirds of the United States than in the western third. 3) November SLP did not contribute to skillful winter temperature prediction as assessed by applying a model to 17 independent cases. 4) The October SST-only model showed slight skill relative to random chance but not compared to persistence. The other ?October? type prediction models showed no skill. 5) The reliability of predictions increased considerably when only those predictions were verified in which the November SST-only model and persistence produced the same forecast. 62% of these forecasts have been correct (using three categories), which was superior to the performance of persistence alone (45% correct) or of the SST-only model alone (47% correct). Geographical and yearly forecast performance differences are discussed as well as predictions made for the recent winter of 1980?81.