What the score means: The 0–100 index summarises atmospheric support for stronger or better-organised convection if a thunderstorm develops. It draws on modelled CAPE, the 700–500 hPa lapse rate and the 850–500 hPa vector wind difference. The categories Minimal, Low, Moderate, High and Severe describe the index strength; even the Severe category is not a prediction that a severe thunderstorm will occur.

What the score does not mean: It is not a probability, an expected storm count, a hail-size forecast or a supercell forecast. It does not directly resolve the local lifting needed to initiate storms. Areas with high severity potential can remain storm-free, while existing storms can move into areas with lower scores.

How to use these maps: Compare severity guidance with thunderstorm development potential, radar, observations and official warnings. Maps are issued every three forecast hours over ten days, but the precise location and timing of convection become less reliable at longer lead times. Read the model run and local valid time printed on each image; gallery headings indicate forecast lead hours.

Index status: This is experimental, uncalibrated model guidance. Scores and categories have not been demonstrated to correspond to fixed chances of severe weather.