The Weather Notebook: Hailstone Rating Scale

Hailstone Rating Scale
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Dave Thurlow, Host

Hi, I'm Dave Thurlow from the Mount Washington Observatory and this is The Weather Notebook. Today, I'm going to start with a quiz. What does an 'F5' refer to? How about a 'category 4'? Finally, what about an H7? To be fair, I'll give you some time to think about it.....Alright, first up, an F5. Now, I'm willing to bet most of you knew that refers to tornado intensity. Next up, Category 4...yep, that's hurricane intensity. But what about H7? Ever hear of that?

Grapefruit-sized hailstone NOAA Photo Library

Well, it actually refers to hail intensity. Hail is a weather event that can cause a lot of damage, but there's no rating for it here in the US. But hail damage is rated in England.

TORRO, the tornado and storm research organization in Oxford, England, has developed a Hailstone Intensity Scale. The scale categorizes damaging and potentially damaging hailstorms from H0 to H10. For example, an H2 hailfall strips leaves from trees, and vegetables and fruit are bruised. An H8 hailfall cracks concrete roof tiles, pavements are pitted and there is risk of serious injury to people caught in such a storm.

The rating scale can be used even if a hailfall occurs over an open area and no structural damage is done. In that case, the intensity is based on hailstone size. Pea sized hail would have an H0 rating. Grapefruit sized hail would have an H8 rating. And hail the size of a coconut would have the highest hailfall rating, an H10.

So, with F5's and category 4's already secured in the American weather lingo, maybe one day, we'll hear about an H7 storm on our local weather report.

The Weather Notebook is underwritten by Subaru, with major support provided by the National Science Foundation.