An ERA-Interim HAILCAST hail climatology for southern Africa

Abstract

Understanding the character of hail is an important part of mitigating its impact on life and property. Climatologies of hail over South Africa are rare and based on observed data with a coarse spatial and temporal resolution. In this article, a hail climatology is created for southern Africa from reanalysis data. Pseudo-soundings are produced from ERA-Interim data and the HAILCAST model, which predicts the diameter of hail, is run using these soundings from 1979 to 2017 at six-hourly intervals. The hail day frequency of the ERA-Interim HAILCAST (EIH) climatology compares well to historical climatologies, although the horizontal resolution of ERA-Interim makes it difficult to pinpoint the exact location of hail in areas of steep topography. Furthermore, the EIH climatology tends to over-predict hail with diameters greater than 3 cm. Detail that was previously unavailable, such as the seasonal and temporal distribution of hail over the entire South Africa, is now available from the EIH climatology. The frequency of hail over the winter rainfall area and over countries bordering South Africa is estimated for the first time. It is recommended that the procedure is repeated with numerical weather prediction models with a higher resolution to determine whether the increased resolution will more accurately identify areas of hail.