Satellite signals are sent via microwave transmission from space. Rain breaks up these signals and can inhibit reception during a heavy downpour.
If your still using the "pizza dish" which is Directv's 18" round dish, I suggest calling Directv and having them install a "slimline" dish, the larger size dish is less susceptible to rain fade.
If your experiencing loss of picture on only local channels, there is nothing you can do. As these are transmitted to the dish on Ka band, which is even more prone to rain interference.
You may also call directv and ask to "have the dish peaked" a poorly aligned dish can experience loss of signal earlier than a properly aligned dish.
If all the above has been done, then sadly it's something you have to live with, as satellite TV goes out sometimes during rain. Cable TV does not have this issue, but some of us do not have cable as an option, or our providers are too expensive.