Weather Tidbits: Hail Size vs. Updraft Speeds

This edition of Weather Tidbits will be discussing the relationship between thunderstorm updraft strength and hail size. Hail stones form via the suspension of rain droplets by the updraft within a pocket of cold air below freezing within the thunderstorm cloud. Eventually, the hailstone’s weight causes it to fall as it can not be supported by the updraft any longer. Stronger updrafts will result in larger hail. For pea-sized hail, an updraft of 24 mph is typically needed. Hail classified as severe is 1.00″ in diameter, the size of a quarter. For hail to achieve this size, the updraft needs to be around 49 mph. For hail to reach 2.00″ in diameter, the size of a hen egg, the updraft needs to be around 69 mph. Grapefruit-sized hail, which is over 4.00″ in diameter, needs an updraft speed of around 98 mph.