Hailstorms are among the most damaging natural hazards in Switzerland, yet drivers of their year-to-year variability remain unclear. Using a 64-year reconstruction of hail days and atmospheric reanalysis, we show that active hail seasons are linked to recurring large-scale circulation patterns and seasonally preconditioned sea and land surface conditions that repeatedly bring warm, moist, unstable environments. Our findings underpin seasonal hail prediction and can support risk preparedness.