In what mesoscale environments do orographic supercells form?

Abstract

The present study investigates potential orographic modifications of mesoscale environments by analyzing prestorm conditions associated with 62 supercells initiated near the Carpathian Mountains in Central Europe during April–September 2015–2019. Environmental diagnostics are derived from three data sources: high-resolution simulations of the COSMO model, ERA5 reanalysis, and upper-air soundings from an intermountain station. From these, multiple convection-related diagnostic variables are calculated, while storms are grouped into three categories based on their mean lifetime translation speed. A broader spatiotemporal context of key parameters, including mixed-layer CAPE, 0-6-km wind shear, 0-3-km storm-relative helicity, and the Supercell Composite Parameter, reveals substantial variability between datasets and across storm speed categories. Several prestorm environments exhibit shear values below commonly expected levels for supercell formation, particularly in slower-moving storms. Spatial analyses show that magnitudes and distributions of parameters differ over complex terrain. While southeastern slopes are often associated with enhanced buoyancy, lee sides of mountains more often exhibit environments favorable for mesocyclone development. These patterns may increase the occurrence of supercell-supportive conditions in specific locations. Among all evaluated variables, precipitable water is the strongest predictor of estimated precipitation intensity during the first 20 minutes, while the Downburst Environment Index best predicts maximum precipitation intensity over the full storm lifetime. Wind shear between the surface and the –10°C isotherm is the strongest predictor of mean storm speed. Spatial distributions of these predictors are also terrain-influenced, but in distinct ways. Overall, terrain can locally enhance both thermodynamic and dynamic components of supercell environments.