Which phenomenon is associated with severe thunderstorms?

Severe thunderstorms are typically characterized by strong vertical wind shear, which refers to the change in wind speed and direction with height in the atmosphere. This vertical wind shear is crucial for the development of powerful storm systems because it allows thunderstorms to build vertically and sustain themselves over time. Strong vertical wind shear enhances the organization of storm cells and can lead to severe weather phenomena such as tornadoes and large hail.

In contrast, the other options do not align with the characteristics of severe thunderstorms. Low wind shear, for instance, is generally associated with weaker storms that lack the necessary organization to develop into severe thunderstorms. Sustained heavy snowfall and ice relate to winter weather systems rather than thunderstorms. Finally, consistent light winds with gradual temperature decreases do not provide the dynamic conditions required for the intense convection found in severe thunderstorms.