Hailstorms: protecting yourself, your vehicle and your home

Thunderclouds can reach very high, up to heights where it is far below freezing. Inside them are powerful updrafts – air that streams rapidly upwards. These updrafts carry water droplets into the cold zones, where they freeze. An ice pellet floating there collects more supercooled water droplets, which freeze onto it, and it grows layer by layer.

The stronger the updraft, the longer a stone can stay in the cloud and the bigger it becomes. Only when it is too heavy to be carried does it fall to the ground. Large stones fall fast and hit with a lot of force. How big hail gets and exactly where it falls depends strongly on the individual storm cell. That is why hail is hard to forecast locally.

Hail often falls in a narrow strip. So it can hail heavily in one part of town while a few streets away it only rains. This is explained in meteorological teaching resources such as the U.S. National Weather Service's JetStream.

Severe-weather warnings often mention hail explicitly. There is then usually some time you can use well: put the car in a garage or car park, bring in garden furniture, parasols and potted plants, retract awnings and close shutters. Shutters protect the window panes, and retracted awnings do not get shredded.

Postpone outdoor plans if you can. If you are out and about, plan a route to a solid building. Timing matters: these preparations are for before the hail starts. Once the first stones are falling, you no longer run to the car to move it – that is a typical mistake in which people get hurt.

In the garden, sensitive plants can be covered with nets or fleece. Greenhouse panes are especially vulnerable; keep away from them during hail.

The car is reasonable protection as long as you stay inside. Slow down, because visibility gets poor and the road can become slippery with hailstones. Stop safely off the carriageway and switch on your hazard lights.

Do not stop on the carriageway or hard shoulder under a bridge, however tempting it seems. Other drivers have the same idea, traffic backs up and following cars can crash into you.

In the stationary car, turn your face away from the windows and cover yourself with a jacket or blanket in case glass breaks. Protect children the same way, for example by having them lean forward with a blanket over their heads. Sunroofs and large panoramic roofs are the most vulnerable spots.

Because hail almost always falls from thunderstorms, the lightning rules apply too. Outdoors, do not shelter under isolated trees or masts; get into a solid building or closed car as quickly as possible. Until then, protect your head with a backpack or your arms. On mountain tours in thunderstorm conditions, abort the tour or do not start it at all.

Indoors, keep away from windows, glass doors and skylights. Standing at the window filming is dangerous if the pane breaks.

After the hail, new dangers appear: roads can be as slippery as in winter, hailstones can block drains, and the heavy rain can lead to flooding. Do not climb onto damaged or slippery roofs; look at damage from the ground.

Hail damage to cars, roofs, facades and windows is sometimes only noticed at a second glance. Photograph it with the date, ideally before repairing anything, and report it to your insurer. A photo with an object for scale later shows how large the stones were.

You can temporarily cover broken windows or roof spots so that no more rain gets in – but only if that can be done safely from the ground or from inside. Work on the roof is for specialist firms. This entry gives no insurance advice; the terms of your policy are what count.