Heatwaves can have devastating impact on society and reliable early warnings at several weeks lead time are needed. Previous studies showed that north-Pacific sea surface temperatures (SST) can provide long-lead predictability for eastern US temperature, mediated by an atmospheric Rossby wave. The exact mechanisms, however, are not well understood. Here we analyze two different Rossby waves associated with temperature variability in western and eastern US, respectively. Causal discovery analyses reveal that both waves are characterized by positive ocean-atmosphere feedbacks at daily timescales. Only for the eastern US, a long-lead causal link from SSTs to the Rossby wave exists, which generates summer temperature predictability. We show that this SST forcing mechanism originates from the evolution of the winter-to-spring Pacific Decadal Oscillation (PDO). During pronounced winter-to-spring PDO phases (either positive or negative) eastern US summer temperature forecast skill more than doubles, providing a temporary window of enhanced long-lead predictability.

热浪可能对社会造成毁灭性影响，因此需要在几周的时间提前发出可靠的预警。先前的研究表明，北太平洋海面温度（SST）可以为美国东部温度提供长期可预测性，由大气罗斯贝波介导。然而，确切的机制尚不清楚。在这里，我们分别分析了与美国西部和东部温度变化相关的两种不同的罗斯比波。因果发现分析表明，这两种波浪都以每日时间尺度上的海洋-大气正反馈为特征。仅在美国东部，存在从 SST 到罗斯比波的长期因果关系，这产生了夏季温度的可预测性。我们表明，这种 SST 强迫机制源于冬季到春季的太平洋年代际涛动 (PDO) 的演变。在明显的冬季到春季 PDO 阶段（正或负）美国东部夏季温度预报技能增加一倍以上，提供了增强长期可预测性的临时窗口。