Long-Term Trends in Convective Weather and Environments in the Southeastern United States

Long-term trends in convective environments suggest a decline in environmental vertical wind shear, however instability (i.e. CAPE) is projected to increase. This may be particularly important in the Southeastern U.S. cool season, where instability is characteristically limited but vertical shear is generally very large and can still be favorable for convection given an overall decline. An increase in cool-season instability could result in more frequent hazardous convective weather (HCW) as well as a change in storm mode, resulting in a different distribution of hazards that can impact a new subset of the population that would not currently expect HCW. We exploit 10-year present and future global time-slice MPAS simulations from Michaelis et. al (2019) as a baseline for studying the change in frequency, mode, and intensity of HCW in the Southeastern U.S. The MPAS model uses a global-scale, 60 km grid which is reduced to a high resolution 15 km grid over the Northern Hemisphere to incorporate the effects of large-scale processes. We identify convective windows using the MPAS convective precipitation, CAPE, and 0-6 km vertical shear parameters at 6-hour output intervals. First, we address whether the location, frequency, and character of these windows is changing over time in the non-convection-allowing MPAS simulations. Subsequently, we use a downscaling approach to study whether the mode and severity of resolved convection will change within the convective environments extracted from MPAS.