What are the defining characteristics of a severe thunderstorm?

The defining characteristics of a severe thunderstorm include wind gusts reaching at least 58 mph, hail that is 1 inch in diameter or larger, or the potential for tornadoes. These criteria are established by the National Weather Service and indicate the storm's capability to produce significant damage and hazardous conditions.

Wind gusts of 58 mph can cause extensive tree damage, power outages, and can be dangerous for high-profile vehicles. The presence of hail that is 1 inch in diameter poses a risk for property damage, particularly to vehicles, roofs, and crops. A severe thunderstorm may also spawn tornadoes, which are among the most destructive phenomena associated with these storms, capable of devastating areas in their path.

The other options reflect conditions that do not meet the criteria for severe thunderstorms. Wind gusts of 40 mph and small hail do not indicate severe classification, and weak wind shear with light rain suggests a lack of the necessary dynamics for severe storm development. Similarly, heavy snowfall and strong winds pertain to winter weather phenomena rather than thunderstorms, and thus are unrelated to the characteristics of severe thunderstorms.