Whenever we get a big hail storm, there are bound to be a few questions — especially when ice the size of golf balls starts to fall from the sky, as it did Tuesday night in Washington, D.C.
1. Yep, hail happens during the summer
Hail is inherently a summertime phenomenon. It forms within strong thunderstorms at high levels where the temperature is always below freezing, even during July. In fact, most precipitation — including the rain that falls in the tropics — actually begins as snow up in the clouds, and only melts into rain when it falls below the freezing line.
On Tuesday night, the temperature was in the upper 80s at ground-level, but the “freezing line” was at 13,000 feet, meaning everything above that line was below 32 degrees. Thunderstorms like last night’s can grow as tall as the jet stream, which is around 40,000 feet.
2. Hail forms within thunderstorms because of strong rising winds
Thunderstorms have updrafts (rising air) and downdrafts (sinking air). When tiny ice crystals are vaulted high into the thunderstorm over and over again, water freezes onto the crystals and they gradually accumulate ice. These stones tumble around the thunderstorm, pulled upward and downward by the competing winds, growing larger in size the longer they remain in the sky.
Once the hail stone is large and heavy enough to outweigh the lift of the updraft, it falls to the ground. This is how we know the largest hail falls in the strongest thunderstorms — the updraft has to be seriously cranking in order to keep ice the size of softballs lofted in the air.
3. Hail stones have layers, like an onion
Since hail is launched up through the storm repeatedly, it can start to grow layers of ice. Each time it takes a trip through the updraft, a new layer accumulates onto the stone. When it falls to the ground, it can have very clear and well-defined bands.
4. Hail can grow as big as volleyballs (as far as we know)
The largest hail stone on record in the U.S. fell on July 23, 2010, in Vivian, S.D. It was eight inches across and 18.62 inches around — which is nearly the size of a volleyball.
Of course, that’s just the largest stone we know of. If car-sized hail fell in a forest and no one was around to measure it, did it really happen? Or something like that.
5. The biggest risk from hail tends to be car and home damage
But watch out for the big ones. The deadliest hailstorm on record supposedly occurred in Uttar Pradesh, India, in 1888. Hail as big as oranges fell, killing 230 people and hundreds of livestock.
Now that we have forecasts and a warning system, hail deaths are much less common. But you really don’t want to be outside when golf balls start falling from the sky. Also, stay away from windows; if there’s wind, hail falls to the ground at an angle. It can rip the siding from houses and wipe out entire windows. The best way to handle that is to pull the blinds and drapes closed to limit flying glass and get out of the way.