Criteria Key

We use threat levels to highlight the probability of both thunderstorm coverage and severity. The threat levels cater for both severe and non-severe thunderstorms, and allow us to forecast more accurately events such as isolated but severe thunderstorms, or widespread non-severe thunderstorms, for example.


Threat Level
Probability of lightning within a 25 mile radius
Low (LOW)
5 - 30 %
Slight (SLGT)
30 - 45 %
Moderate (MDT)
45 - 60 %
High (HIGH)
> 60 %


We classify a severe thunderstorm as one that poses a significant threat to life and/or property, using the criteria below. If any of the following criteria are forecast, a SVR threat level may be issued to highlight the areas at risk of severe convective weather. This does not necessarily mean severe convective weather will occur in all parts of the highlighted area, but it indicates the potential for such an occurrence, even if quite localised.

Threat Level
Severe (SVR)
  • 25mm or more precipitation in 3 hours or less
  • Hail greater than 2.0cm in diameter
  • Wind gusts greater than 55mph
  • Tornadoes