Broadcast range
The local terrain can also play a major role in limiting broadcast range. Mountain ranges block FM broadcasts, AM broadcasts, and TV broadcasts, and other signals in the VHF and especially UHF ranges, respectively. This terrain shielding occurs when the line of sight is blocked by something through which the radio waves cannot pass, particularly stone. At times this may be moot due to weather, such as when the tall cumulonimbus clouds of a squall line of thunderstorms reflect the signal over the top, like an extremely tall radio tower. Conversely, heavy rain may attenuate the range of even local stations. ATSC digital television is affected by wind and trees (even if not surrounding the transmitter or receiver locations), apparently related to its use of 8VSB modulation instead of COFDM.
Air-mass thunderstorm
Convective rain, or showery precipitation, occurs from cumulonimbus clouds. It falls as showers with rapidly changing intensity. Convective precipitation falls over a certain area for a relatively short time, as convective clouds such as thunderstorms have limited horizontal extent. Most precipitation in the tropics appears to be convective. Graupel and hail are good indicators of convective precipitation and thunderstorms. In mid-latitudes, convective precipitation is intermittent and often associated with baroclinic boundaries such as cold fronts, squall lines, and warm fronts. High rainfall rates are associated with thunderstorms with larger raindrops. Heavy rainfall leads to fading of microwave transmissions starting above the frequency of 10 gigahertz (GHz), but is more severe above frequencies of 15 GHz.