The proactive plan should commence in the days before the activity, where weather forecasts provide important warning of possible thunderstorm activity.
(ii) Match Day Increased awareness of lightning risk should continue on the match day until the activity has finished.
The most basic level of warning involves observation of the weather in the local area.
(i) 30 / 30 Rule
The “30/30” rule serves as a guide for the suspension and subsequent resumption of activities. The overall principle is to seek shelter when the lightning activity is too close.
The observation of approaching storm clouds, the first flash of lightning or clap of thunder, no matter how far away should heighten lightning awareness. The level of risk depends on one‟s location (direction and distance) relative to the storm cell and the direction in which the storm system is traveling.
A simple method of determining the distance to the storm cell is to measure the time elapsed from when the lightning flash is observed and when the associated clap of thunder is heard.
Light travels faster than sound. Assuming that the light from the flash reaches the observer instantaneously, and knowing that sound takes approximately three (3) seconds to travel one (1) kilometre, the distance can be determined by using the following rule:
Distance (in Km) = Time from observing the flash to hearing thunder (in seconds)/3
It is important to remember that lightning may be obscured by clouds so it must be assumed that when thunder is heard, lightning is in the vicinity. In such cases, careful judgment must be used to determine whether a threat exists.
The first part of the “30/30” rule is a guide to the postponement or suspension of activities. Most experts agree that the accepted „safe‟ distance from lightning is less than 10km. This means that as the time interval between observing the flash and hearing the thunder approaches 30 seconds, all those in exposed areas should be seeking or already inside safe shelters. A storm cell with lightning activity within 10km constitutes a threat.
The second part of the 30/30 rule provides the criteria for the resumption of activity which is applicable to decisions made with BOM access as well. Here, it is recommended that people wait a minimum of 30 minutes after the last sighting of lightning or sound of thunder. This figure is based on the observation that the typical storm moves at about 40km/h. Thus, waiting 30 minutes allows the thunderstorm to be about 20km away, minimising the likelihood of a nearby lightning strike. Note: 60 minutes is the maximum delay time.
It is important to emphasize that blue skies and lack of rainfall are not adequate reasons to breach the 30 minute minimum return-to-activity rule.