Trends in the extremes of environments associated with severe US thunderstorms
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Severe thunderstorms can have devastating impacts. Concurrently high values of Convective Potential Energy (CAPE) and Storm Relative Helicity (SRH) are known to be favourable to severe weather, so we consider their extreme values for a large area of the contiguous US over the period 1979-2015. We use extreme-value theory and a multiple testing procedure to show that there is a significant time trend in the extremes for CAPE maxima in April, May and June, for SRH maxima in May, and for maxima of PROD=√(CAPE)× SRH in April, May and August. Moreover, we show that the El Niño-Southern Oscillation explains variation in the extremes of PROD and SRH in February. Our results imply that the risk of severe thunderstorms in April and May tends to increase in parts of the US where this risk was already high and that the storm risk in February tends to be higher over the main part of the region during La Niña years.
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