 The US National Weather Service has a 2.5 cm (1 in) or greater in diameter threshold, effective January 2010, an increase over the previous threshold of ¾-inch hail.Other countries have different thresholds according to local sensitivity to hail; for instance grape growing areas could be adversely impacted by smaller hailstones.Hailstones can be very large or very small, depending on how strong the updraft is