The Weather Project · Northern Territory
Thunderstorm Severity Potential
GFS guidance on the atmosphere’s capacity to support stronger or more organised thunderstorms if convection develops. The 0–100 Severity Potential index combines CAPE, mid-level lapse rates and 850–500 hPa wind shear. It is conditional environmental potential, not a probability of severe weather.
Understanding thunderstorm environmental potential
Thunderstorm Development Potential
Thunderstorm Development Potential is a 0–100 environmental index of conditions favourable for convective development, using instability, moisture, lapse rates and inhibition. Higher scores indicate a more supportive environment for storm formation. It does not predict the percentage of an area affected, how widespread thunderstorms will be, or a calibrated probability of storms occurring.
Thunderstorm Severity Potential
The Thunderstorm Severity Potential index assesses the atmosphere’s capacity to support stronger or more organised thunderstorms if convection develops. Using GFS forecast data, it combines atmospheric instability (CAPE), mid-level temperature lapse rates and wind shear between 850 and 500 hPa. Higher scores indicate environments more supportive of vigorous convection, including organised storms or intense, short-lived thunderstorms. The 0–100 scale is an environmental index, not a probability of severe weather or a prediction of hail size, damaging winds or storm type. A high severity score does not necessarily mean thunderstorms will occur, while significant storms can still develop in environments with moderate scores.
Thunderstorm Composite
The Thunderstorm Composite provides an overall assessment of atmospheric conditions favourable for thunderstorm development and potential intensity. It combines the Development Potential and conditional Severity Potential indices into a single 0–100 score, placing greater emphasis on the likelihood of conditions supporting storm formation than on severity alone. Higher values indicate a more favourable combination of ingredients for thunderstorm development and potentially stronger convection. The composite is intended to highlight areas of elevated thunderstorm potential, not to forecast exact storm locations, timing or intensity. Scores are experimental environmental guidance rather than calibrated probabilities, and should be considered alongside radar, observations and official weather warnings.
Retain the map’s existing score categories as environmental potential bands, not percentage probabilities. GFS maps are 3-hourly; read the run and local valid time on each map. Longer forecast leads have lower forecast skill.