Zonal Wind Indices to Reconstruct CONUS Winter Precipitation


Seasonal precipitation forecasts over the contiguous United States (CONUS) during the 2015-16 El NiƱo exhibited significant bias over many regions, especially in the Western United States where seasonal information is particularly valuable for reservoir operation. Diagnosing the origin of this bias requires understanding the empirical signal from tropical heating to mid-latitude precipitation. In this paper, we find that atmospheric zonal wind indices computed over the region typically associated with the winter jet stream provide a skillful, spatially distributed, linear prediction of precipitation over CONUS, over all winters (Jan-Mar; JFM). Furthermore, we show that more (less) central (eastern) Pacific Ocean heating may have contributed to the unexpected 2016 JFM CONUS precipitation and that this was likely predictable based on antecedent (Dec) sea surface temperatures. The zonal wind indices act as intermediate variables in a causal chain and our analyses provide support for the potential for empirical prediction and also a diagnostic for physics based models to help improve forecasts.

In Geophysical Research Letters