Actually, it is not the tuner in the TV that is the problem unless it is raining hard. The HD satellite receiver DVR gets the weak signal and records it that way. Typically when I am using the tuner in the TV I am using an off air antennas, the rabbit ears.
Typically when the weather is fine the only time this happens is when getting the satellite digital signal passed through to the HDTV and only when viewing local stations. Switching inputs to rabbit ears and watching the same local HD channel solves the problem. Obviously if there is severe rain this can happen at any time with either source.
Doing mushrooms. LOL OK let me describe this a bit better. I will give you two examples of how this looks. As the signal weakens the sound starts distorting to indicate that the picture is about to degrade. Slowly the picture begins to have different color blocks appear off and on. As this progresses the picture appears to blur and it strongly resembles a 'Picasso" painting but there is still motion. "If" it worsens it may freeze and or become totally unrecognizable.
In its worse state and for my second example you have to think about looking at a jpg file and zooming in. As you greatly zoom in the pixels become larger and you see less details of the picture. this is what the screen looks like as it freezes and or just before the screen goes blank. This can go on for an entire episode of a show. then suddenly every thing is fine for several seconds and it goes through this cycle over and over. If it is exceptionally bad I will get a black screen for a few seconds during the cycle.