4. Forecast Applications

Convection » Air Mass Thunderstorms Forecasting Air Mass Thunderstorms

Photo of a cumulus cloud

Air mass thunderstorms develop when synoptic forcing is weak but the boundary layer is moist and relatively warm. Vertical wind shear is usually weak, and parcel lifting is due primarily to buoyant energy, which can be estimated from the convective available potential energy (CAPE)convective available potential energy (CAPE). The environmental lapse rate must be conditionally unstableconditionally unstable and the air must have sufficient moisture that rising air parcels will saturate and continue rising beyond their level of free convectionlevel of free convection. A capping inversion may be present during the early morning and can delay initiation until the boundary layer is warmed to its convective temperatureconvective temperature. Recall that the convective temperature is the surface temperature that must be reached to start the formation of convective clouds by surface heating.

In some instances, the environmental lapse rate may be more unstable and the vertical wind shear may be stronger. In these cases, the convection may no longer be of the ordinary air mass-type, and can develop, instead, into severe thunderstormssevere thunderstorms, accompanied by hail, strong winds and, in rare instances, tornadoes. Sounding parameters for assessing the potential for severe convection are discussed in the Severe Thunderstorms section.