Storm Indices Forecast

Storm Index is a special index for predicting the possibility of storms during the upcoming forecast period. The Storm index uses Lifted Index, Severe Index, Convection Index and Dewpoint in determining the index. A Storm Index value of 1-3 indicates an increasing possibilty for storms, and a value above 3 indicates a strong likelihood they will develop. The Severe Index indicates the forecasted severity of the storm. A Severe Index value of 4-5 indicates a likely thunderstorm. Severe Index values of 5 or greater indicate a thunderstorm that is possibly severe. Lifted Index is a common measure of atmospheric instability. Negative values indicate instability - the more negative, the more unstable the air is, and the stronger the updrafts are likely to be with any developing thunderstorms. However, there are no "magic numbers" or threshold Lifted Index values below which severe weather becomes imminent. The 'negative' Lifted Index values are represented on the chart as 'positive' values for clarity. Thus, the higher the Lifted Index value shown, the more unstable the air is.