The Madden–Julian Oscillation (MJO) is the dominant mode of intraseasonal variability in the tropics and has a documented influence on extratropical extreme weather through modulation of synoptic atmospheric conditions. MJO phase has been correlated with anomalous tornado and severe hail frequency in the United States (US). However, the robustness of this relationship is unsettled, and the variability of physical pathways to modulation is poorly understood, despite the socioeconomic impacts that tornadoes and hail evoke. We approached this problem using pentad MJO indices and practically perfect severe weather hindcasts. MJO lifecycles were cataloged and clustered to document variability and potential pathways to enhanced subseasonal tornado and hail predictability. Statistically significant increases in US tornado and hail probabilities were documented 3–4 weeks following the period of the strongest upper-level divergence for the 53 active MJO events that propagated past the Maritime continent, contrasting with the 47 MJO events that experienced the barrier effect, during boreal spring 1979–2019. The 53 MJO events that propagated past the Maritime continent revealed three prevailing MJO evolutions—each containing unique pathways and modulation of US tornado and hail frequency—advancing our knowledge and capability to anticipate these hazards at extended lead times.

Madden-Julian 涛动 (MJO) 是热带季节内变率的主要模式，并通过调节天气大气条件对温带极端天气产生影响。MJO 阶段与美国 (US) 的异常龙卷风和严重冰雹频率相关。然而，尽管龙卷风和冰雹会引发社会经济影响，但这种关系的稳健性并不确定，而且人们对调节的物理途径的可变性知之甚少。我们使用 pentad MJO 指数和几乎完美的恶劣天气后报来解决这个问题。对 MJO 生命周期进行编目和聚类，以记录增强次季节性龙卷风和冰雹可预测性的可变性和潜在途径。在传播经过海洋大陆的 53 个活跃 MJO 事件的上层分歧最强时期之后的 3-4 周，美国龙卷风和冰雹概率的统计显着增加，与经历障碍效应的 47 个 MJO 事件形成对比，在 1979 年至 2019 年的北方春季期间。传播到海洋大陆的 53 次 MJO 事件揭示了三种主要的 MJO 演变——每一次都包含独特的路径和美国龙卷风和冰雹频率的调制——提高了我们在延长的提前期预测这些危险的知识和能力。在 1979 年至 2019 年的北方春季期间。传播到海洋大陆的 53 次 MJO 事件揭示了三种主要的 MJO 演变——每一次都包含独特的路径和美国龙卷风和冰雹频率的调制——提高了我们在延长的提前期预测这些危险的知识和能力。在 1979 年至 2019 年的北方春季期间。传播到海洋大陆的 53 次 MJO 事件揭示了三种主要的 MJO 演变——每一次都包含独特的路径和美国龙卷风和冰雹频率的调制——提高了我们在延长的提前期预测这些危险的知识和能力。