question: Why does thunder usually occur with lightning strikes to the ground and not the cloud to cloud lighting?
comment: Not true. If you define thunder as the sound produced when the lightning discharges, it always happens regardless of cloud to cloud or cloud to ground. However, the cloud to cloud may be far enough away that all you hear is a rumbling sound and not the more distinctly explosive thunder sound from a close by lightning strike.
passages: Intra-cloud lightning most commonly occurs between the upper anvil portion and lower reaches of a given thunderstorm. This lightning can sometimes be observed at great distances at night as so-called "sheet lightning". In such instances, the observer may see only a flash of light without hearing any thunder.
   Section::::Types.:Cloud to cloud (CC) and intra-cloud (IC).
  
  Lightning discharges may occur between areas of cloud without contacting the ground. When it occurs between two separate clouds it is known as "inter-cloud lightning", and when it occurs between areas of differing electric potential within a single cloud it is known as "intra-cloud lightning". Intra-cloud lightning is the most frequently occurring type.
   Cloud-ground lightning typically consist of two or more return strokes, from ground to cloud. Later return strokes have greater acoustic energy than the first.
  
  Section::::Perception.
   Cloud-to-ground lightning frequently occurs within the phenomena of thunderstorms and have numerous hazards towards landscapes and populations. One of the more significant hazards lightning can pose is the wildfires they are capable of igniting. Under a regime of low precipitation (LP) thunderstorms, where little precipitation is present, rainfall cannot prevent fires from starting when vegetation is dry as lightning produces a concentrated amount of extreme heat. Direct damage caused by lightning strikes occurs on occasion. In areas with a high frequency for cloud-to-ground lightning, like Florida, lightning causes several fatalities per year, most commonly to people working outside.
   The result is that the upper part of the thunderstorm cloud becomes positively charged while the middle to lower part of the thunderstorm cloud becomes negatively charged.
   Because the concentrated charge within the cloud must exceed the insulating properties of air, and this increases proportionally to the distance between the cloud and the ground, the proportion of CG strikes (versus cloud-to-cloud (CC) or in-cloud (IC) discharges) becomes greater when the cloud is closer to the ground. In the tropics, where the freezing level is generally higher in the atmosphere, only 10% of lightning flashes are CG. At the latitude of Norway (around 60° North latitude), where the freezing elevation is lower, 50% of lightning is CG.
   Cloud-to-ground lightning frequently occurs within the phenomena of thunderstorms and have numerous hazards towards landscapes and populations. One of the more significant hazards lightning can pose is the wildfires they are capable of igniting. Under a regime of low precipitation (LP) thunderstorms, where little precipitation is present, rainfall cannot prevent fires from starting when vegetation is dry as lightning produces a concentrated amount of extreme heat. Wildfires can devastate vegetation and the biodiversity of an ecosystem. Wildfires that occur close to urban environments can inflict damages upon infrastructures, buildings, crops, and provide risks to explosions, should the flames be exposed to gas pipes. Direct damage caused by lightning strikes occurs on occasion. In areas with a high frequency for cloud-to-ground lightning, like Florida, lightning causes several fatalities per year, most commonly to people working outside.
   A lightning strike or lightning bolt is an electric discharge between the atmosphere and an object. They mostly originate in a cumulonimbus cloud and terminate on the ground, called cloud to ground (CG) lightning. A less common type of strike, called ground to cloud (GC), is upward propagating lightning initiated from a tall grounded object and reaches into the clouds. About 25% of all lightning events worldwide are strikes between the atmosphere and earth-bound objects. The bulk of lightning events are intra-cloud (IC) or cloud to cloud (CC), where discharges only occur high in the atmosphere. Lightning strikes the average commercial aircraft at least once a year, but modern engineering and design means this is rarely a problem. The movement of aircraft through clouds can even cause lightning strikes.
   BULLET::::- A ground-based lightning network must be able to detect a flash with at least three antennas to locate it with an acceptable margin of error. This often leads to the rejection of cloud-to-cloud lightning, as one antenna might detect the position of the flash on the starting cloud and the other antenna the receiving one. As a result, ground-based networks have a tendency to underestimate the number of flashes, especially at the beginning of storms where cloud-to-cloud lightning is prevalent.
   It is possible for one end of the leader to fill the oppositely-charged well entirely while the other end is still active. When this happens, the leader end which filled the well may propagate outside of the thundercloud and result in either a cloud-to-air flash or a cloud-to-ground flash. In a typical cloud-to-ground flash, a bidirectional leader initiates between the main negative and lower positive charge regions in a thundercloud. The weaker positive charge region is filled quickly by the negative leader which then propagates toward the inductively-charged ground.
   Lightning is usually produced by cumulonimbus clouds, which have bases that are typically 1–2 km (0.6–1.25 miles) above the ground and tops up to in height.
   Many factors affect the frequency, distribution, strength and physical properties of a typical lightning flash in a particular region of the world. These factors include ground elevation, latitude, prevailing wind currents, relative humidity, proximity to warm and cold bodies of water, etc. To a certain degree, the ratio between IC (in-cloud or intracloud), CC (cloud-to-cloud) and CG (cloud-to-ground) lightning may also vary by season in middle latitudes.
   Contrary to popular belief, positive lightning flashes do not necessarily originate from the anvil or the upper positive charge region and strike a rain-free area outside of the thunderstorm. This belief is based on the outdated idea that lightning leaders are unipolar in nature and originating from their respective charge region.
   The cloud must develop to a certain vertical extent before lightning is produced, so generally weather radar will indicate a developing storm before a lightning detector does. It is not always clear from early returns if a shower cloud will develop into a thunderstorm, and weather radar also sometimes suffers from a "masking" effect by attenuation, where precipitation close to the radar can hide (perhaps more intense) precipitation farther away. Lightning detectors do not suffer from a masking effect and can provide confirmation when a shower cloud has evolved into a thunderstorm.
   A typical cloud-to-ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of tall, from within the cloud to the ground's surface. The actual discharge is the final stage of a very complex process. At its peak, a typical thunderstorm produces three or more "strikes" to the Earth per minute. Lightning primarily occurs when warm air is mixed with colder air masses, resulting in atmospheric disturbances necessary for polarizing the atmosphere. However, it can also occur during dust storms, forest fires, tornadoes, volcanic eruptions, and even in the cold of winter, where the lightning is known as thundersnow. Hurricanes typically generate some lightning, mainly in the rainbands as much as from the center.
   Section::::Types.
  
  There are three primary types of lightning, defined by what is at the "ends" of a flash channel.
  
  BULLET::::- Intracloud (IC), which occurs within a single thundercloud unit
  
  BULLET::::- Cloud to cloud (CC) or intercloud, which starts and ends between two different "functional" thundercloud units
  
  BULLET::::- Cloud to ground (CG), that primarily originates in the thundercloud and terminates on an Earth surface, but may also occur in the reverse direction, that is ground to cloud
   Although commonly associated with thunderstorms at close range, lightning strikes can occur on a day that seems devoid of clouds. This occurrence is known as "A Bolt From the Blue"; lightning can strike up to 10 miles from a cloud.
   Lightning at a sufficient distance may be seen and not heard; there is data that a lightning storm can be seen at over 100 miles whereas the thunder travels about 20 miles. Anecdotally, there are many examples of people saying 'the storm was directly overhead or all-around and yet there was no thunder'. There is no coherent data available.
  
  Section::::Effects.:High-energy radiation.
   The three main kinds of lightning are distinguished by where they occur: either inside a single thundercloud, between two different clouds, or between a cloud and the ground. Many other observational variants are recognized, including "heat lightning", which can be seen from a great distance but not heard; dry lightning, which can cause forest fires; and ball lightning, which is rarely observed scientifically.
   BULLET::::- Clear-air lightning describes lightning that occurs with no apparent cloud close enough to have produced it. In the U.S. and Canadian Rockies, a thunderstorm can be in an adjacent valley and not observable from the valley where the lightning bolt strikes, either visually or audibly. European and Asian mountainous areas experience similar events. Also in areas such as sounds, large lakes or open plains, when the storm cell is on the near horizon (within ) there may be some distant activity, a strike can occur and as the storm is so far away, the strike is referred to as a bolt from the blue. These flashes usually begin as normal intracloud lightning flashes before the negative leader exits the cloud and strikes the ground a considerable distance away. Positive clear-air strikes can occur in highly sheared environments where the upper positive charge region becomes horizontally displaced from the precipitation area.
   Nimbostratus, unlike cumulonimbus, is not associated with thunderstorms, however at an unusually unstable warm front caused as a result of the advancing warm air being hot, humid and unstable, cumulonimbus clouds may be embedded within the usual nimbostratus. Lightning from an embedded cumulonimbus cloud may interact with the nimbostratus but only in the immediate area around it. In this situation with lightning and rain occurring it would be hard to tell which type of cloud was producing the rain from the ground, however cumulonimbus tend to produce larger droplets and more intense downpours. The occurrence of cumulonimbus and nimbostratus together is uncommon, and usually only nimbostratus is found at a warm front.
   The best studied and understood form of lightning is cloud to ground (CG). Although more common, intracloud (IC) and cloud to cloud (CC) flashes are very difficult to study given there are no "physical" points to monitor inside the clouds. Also, given the very low probability lightning will strike the same point repeatedly and consistently, scientific inquiry is difficult at best even in the areas of high CG frequency. As such, knowing flash propagation is similar amongst all forms of lightning, the best means to describe the process is through an examination of the most studied form, cloud to ground. 
   Lightning or electricity is the "pilot" or guide for the cloud. Lightning is attracted to the "genii" in the earth which results in lightning flashes. The genii symbolise the positive charge of the surface of the earth while the cloud possesses a negative charge.
   After a cloud, for instance, has started its way to becoming a lightning generator, atmospheric water vapor acts as a substance (or insulator) that decreases the ability of the cloud to discharge its electrical energy. Over a certain amount of time, if the cloud continues to generate and store more static electricity, the barrier that was created by the atmospheric water vapor will ultimately break down from the stored electrical potential energy. This energy will be released to a local oppositely charged region, in the form of lightning. The strength of each discharge is directly related to the atmospheric permittivity, capacitance, and the source's charge generating ability.
   Another term used for cloud–cloud or cloud–cloud–ground lightning is "Anvil Crawler", due to the habit of charge, typically originating beneath or within the anvil and scrambling through the upper cloud layers of a thunderstorm, often generating dramatic multiple branch strokes. These are usually seen as a thunderstorm passes over the observer or begins to decay. The most vivid crawler behavior occurs in well developed thunderstorms that feature extensive rear anvil shearing.
  
  Section::::Types.:Observational variations.
  
presuppositions: Thunder does not occur with the cloud to cloud lightning. Thunder usually occurs when lightning strikes the ground, not when lightning goes cloud to cloud.
corrections: Thunder occurs with both the cloud to cloud and cloud to ground lightning though the former one is far away and is just a  rumbling sound. Thunder always happens regardless of cloud to cloud or cloud to ground lightning.
raw_presuppositions: Thunder does not occur with the cloud to cloud lightning. Thunder usually occurs when lightning strikes the ground, not when lightning goes cloud to cloud.
raw_corrections: Thunder occurs with both the cloud to cloud and cloud to ground lightning though the former one is far away and is just a  rumbling sound. Thunder always happens regardless of cloud to cloud or cloud to ground lightning.