Bing,
My understanding is that there are the necessary procedures in place wrt how crews/DDHs are informed of rotors. However, consider the unique status that MPC has (discussed previously) if the main was blacked what is the mitigation? Furthermore, if, as you say the forecast is unreliable, then the option to turn an ac around/divert could be argued as the safest option 'knowns v unknowns' however much it is a pain in the backside to go elsewhere.