What does the heavy dashed line that forms a large rectangular box on a Radar Summary Chart refer to?

The heavy dashed line forming a large rectangular box on a Radar Summary Chart indicates a severe weather watch area. This specific marking serves to alert pilots to regions where severe weather conditions are forecasted and where potential hazards such as thunderstorms or severe turbulence might occur. This designation is critical for flight planning and safety, as it allows pilots to maintain awareness and make informed decisions about their routes and altitudes to avoid adverse weather conditions that can threaten both the aircraft and occupants. Understanding these visual indicators is essential for navigating safely through areas where severe weather is possible.