Monday, 8 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
In the United States, convective severe weather – in the form of tornadoes, hail, severe winds, lightning, and flash flooding – claims hundreds of lives and causes billions of dollars in property damage each year. While convective severe weather is inherently mesoscale in nature, it typically occurs during favorable synoptic-scale regimes characterized by high values of parameters such as convective available potential energy, vertical wind shear, and precipitable water. Based on these parameters and numerical weather prediction (NWP) model guidance, forecasters at the Storm Prediction Center currently offer severe weather outlooks with lead times of up to 8 days to the public. Here we show the potential to extend these lead times by harnessing information on the current state of the Madden-Julian Oscillation (MJO). Using reanalysis data, we find that the MJO modulates both when and where severe weather regimes are likely to occur at lead times extending into subseasonal-to-seasonal (S2S) time scales (~ 2 to 6 weeks). Moreover, we find that the MJO’s intraseasonal modulation of severe weather regimes is itself modulated by interannual modes of climate variability such as the El-Niño Southern Oscillation (ENSO), the Arctic Oscillation (AO), and the Quasi-Biennial Oscillation (QBO). To demonstrate the robustness of these modulations, we link them to observed storm reports of tornadoes, hail, and severe winds. Furthermore, we create an empirical prediction scheme for anomalous severe weather regimes based solely on the MJO, ENSO, AO, and QBO as predictors. We demonstrate skillful “forecasts of opportunity” with lead times extending into S2S time scales, exceeding the ability of state-of-the-art NWP models. In light of the traumatic impacts associated with convective severe weather, even modest gains in its subseasonal prediction have great worth in supporting early action decision making and thereby benefit numerous sectors of society.
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