The phenomenon is triboelectrification:
Flying through high-level clouds can generate "P-static" (P for precipitation), which can create a corona of static around the rocket that interferes with radio signals sent by or to the rocket. This would create problems when the rocket tries to transmit data down to the ground or if the Range Safety Officer at Cape Canaveral Air Force Station needed to send a signal to the flight termination system.Okay, I understand the reasoning here, but come on: we can't build telemetry systems which can punch through that nonsense?
...sitting here watching the rocket sit on the pad. Twenty minutes ago they were all green; I said, "Move up the count and launch now." They didn't; and so with 15 minutes to go before resuming from T-4:00 the weather conditions went red.
Because of clouds.