There are conventions used in the measurement of weather radar reflectivity...
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When describing weather radar returns, pilots, dispatchers, and air traffic controllers will typically refer to three return levels:
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- level 1 corresponds to a green radar return, indicating usually light precipitation and little to no turbulence, leading to a possibility of reduced visibility.
- level 2 corresponds to a yellow radar return, indicating moderate precipitation, leading to the possibility of very low visibility, moderate turbulence and an uncomfortable ride for aircraft passengers.
- level 3 corresponds to a red radar return, indicating heavy precipitation, leading to the possibility of thunderstorms and severe turbulence and structural damage to the aircraft.
Aircraft will try to avoid level 2 returns when possible, and will always avoid level 3 unless they are specially-designed research aircraft.
This flight and flight-plan took the aircraft through Yellow and Red areas on the weather radar plot, and contact was lost as it approached the second red area, almost to within a mile.
Those are the known facts...