微风拂面

Thunderstorms require an unstable troposphere, adequate moisture and enough lift to realize the unstable air. 

An air mass thunderstorm is in reference to a relatively weak thunderstorm that usually does not last much longer than an hour, moves slowly and does not produce severe weather. Another term that means the same as an air mass thunderstorm is a garden variety thunderstorm. 

Air mass thunderstorms tend to occur within a maritime tropical air mass. The wind shear is weak and this is why the air mass storms are not severe, do not last long and do not move quickly. The main threats from an air mass thunderstorm are lightning and brief heavy rain. The instability tends to be weaker with air mass thunderstorms. For example, the CAPE value for an air mass thunderstorm will often be more than half as less as CAPE values associated with severe thunderstorms. Since wind shear is less in the air mass thunderstorm environment, the Helicity values are often less than those associated with severe thunderstorms. The lifting mechanisms that generate air mass thunderstorms tend to be weaker. While a severe thunderstorm may have lifting from a strong approaching cold front, strong upper level jet streak or a strong low level convergence boundary, the lifting for an air mass thunderstorm tends to be more subtle such as lifting generated by daytime heating and weak low level convergence. Because of this air mass thunderstorms tend to occur in the afternoon hours. Air mass thunderstorms are common in the summer along and near the Gulf coast states and in other areas where the conditions are right for them to occur. 

from: http://www.theweatherprediction.com/habyhints2/458/