24 hr National Storm Forecast: The yellow-brown shading indicates the amount of CAPE (Convective Available Potential Energy) in the atmosphere, which is a good indicator of the potential for strong thunderstorms and severe weather. High values of CAPE indicate that most (but not necessarily all) conditions exist for strong thunderstorms. The scale is given in the top right corner of the map. CAPE measures the amount of energy available for convection throughout the depth of the atmosphere up to the limit of convection. It is also directly related to the maximum potential vertical speed within an updraft. While there are no hard-and-fast rules, readings over 1000 joules per kilogram (J/kg) would suggest the likelihood of thunderstorms, and over 2500 the possibility of severe storms.