The shortest lesson in the module, and the one where being wrong costs the most.

In this lesson you will

  • State the hail sizes that pose injury risk and the correct sheltering behavior.
  • State the downburst, flying-debris and downed-power-line hazards.
  • State the driving hazards high wind presents to high-profile vehicles.
Read the source as well as this page
Everything below is a summary of published NWS safety guidance, and a summary is the wrong thing to rely on alone when the subject is whether you get hurt. The NWS thunderstorm and hail safety pages are linked at the foot of this lesson. Read them. Nothing here is meant to replace them.

Hail

  • Do not go out to collect hail while it is falling. Severe hail causes bruising, cuts and head injuries, and the largest stones are falling at highway speed.
  • Wait for the thunder to stop, and then some. The NWS guidance for going back outside after a storm is about thirty minutes past the last thunder. The stone will have shrunk; report that you measured it late.
  • Indoors, get away from windows. Hail breaks glass, and it arrives with the wind behind it.
  • In a vehicle, stop somewhere safe first: away from trees and power lines, off the carriageway. Then keep your back to the windows and stay low. Do not stop under an overpass.

Wind

  • Treat any thunderstorm outflow as a wind hazard. A downburst arrives with winds comparable to a tornado and almost no warning, and lesson 4 covered why you often cannot see it coming through the rain.
  • Flying debris is what actually injures people, not the wind itself. Put a wall between you and it.
  • Never approach a downed power line. Assume it is energised, whether or not it is sparking or arcing, and whether or not the lights are out. Report it and keep people away.
  • High-profile vehicles are at rollover risk in crosswinds and gust fronts: RVs, box trucks, anything towing. If you are driving one and a gust front is coming, stop somewhere sheltered before it arrives.
The NWS says this, and means it
The National Weather Service values your safety more than it values your observations. There is no report worth being hurt for. The report you do not make because you moved is the correct decision, every time, and nobody will second-guess it.

Check yourself

Hail has stopped and you can see a stone the size of a baseball in the driveway. The last thunder was about five minutes ago. What now?

  1. Wait. Roughly thirty minutes past the last thunder, then measure it and note that the measurement was late
  2. Collect it immediately, before it melts and the measurement is lost
  3. Photograph it from a window and do not go out at all
  4. Collect it now but stay under the eaves
Hint

One option trades a real risk for a better number. Weigh what each is worth.

Answer

Wait. Roughly thirty minutes past the last thunder, then measure it and note that the measurement was late

Melting costs you accuracy and the storm can cost you more than that. Wait for the thunder to clear, then measure and say the measurement was delayed: a stone reported as "baseball, measured 30 minutes after it fell" is honest and usable. The US record stone from Vivian, South Dakota shrank before anybody could measure it, and it still holds the record.

Sources

  1. NWS Weather Spotter's Field Guide (YPA-201154, June 2011)
  2. NWS thunderstorm and hail safety pages