The Influence of the Madden Julian Oscillation on Severe Convective Storm Likelihood

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Sunday, 4 January 2015
Hank A. Leslie, United States Naval Academy, Annapolis, MD; and B. S. Barrett

It is well studied how synoptic-scale parameters, such as convective available potential energy (CAPE), 0-6 km vertical wind shear, 0-1 and 0-3 km storm relative helicity (SRH), and various other parameters, impact the development and severity of convective storms. However, it has not been well studied how the Madden-Julian Oscillation (MJO), the leading planetary-scale oscillation on intraseasonal (30-60 day) time scales, impacts severe weather events, specifically severe convective storms. Thus, for this study, relationships between the intraseasonal variability of severe connective storms within the United States and the Madden-Julian Oscillation were explored. To do this, frequencies of tornado, hail, and severe wind days were compared for the eight active phases of the Real-time multivariate MJO (RMM) index. The months of April, May and June were specifically studied to observe how anomalies of CAPE, 0-6 km vertical wind shear, 0-1 km SRH, and 0-3 km SRH might co-vary with anomalies of tornado, hail, and severe wind days within each month. By establishing statistical relationships between the MJO and severe weather events, the predictability of such events could potentially be extended beyond the current operational limit of around eight days, particularly as prediction skill of phase and amplitude of the MJO increases. Furthermore, knowledge of relationships between particular MJO phases (e.g., a planetary-scale phenomenon) and likelihood of severe weather (e.g., meso- and synoptic-scale phenomena), particularly for a particular region of the United States, could lead to increased predictability on the meso- and synoptic scales.