Check it out - Scientific American Lightning Article.

The May Scientific American has an article by Florida Tech physicist Joseph Dwyer, discussing the initiation and propogation of lightning as it creates a channel through the atmosphere. While not up to the high standards of pre-90's SciAm articles, the piece is informative and well worth reading.

It is true that the electric fields necessary for initial electrical breakdown in thunderstorms have never been measured by electric field meters. In fact, except for a few anomolous readings, we are off by atleast an order of magnitude. The most likely hypothesize is that corona point charge is so localized that it is impossible to actually measure the electric field necessary for initial electrical breakdown and lightning. New theories have applied quantam physics and suggested that cosmic rays provide the electron excitment necessary for acceleration and initiation of breakdown.

For the foreseeable future the traditional mix of inductive and non-inductive charging people and the cosmic ray believers will duke it out for which theory explains the initiation of lightning. It is just too difficult and dangerous to get in-situ observations of lightning and to understand the exact processes that are occurring to initiate it. With the advent of dual-pol radar it has given extreme confidence that non-inductive graupel-ice interactions are a pre-requisite for lightning initiation, but this still does not satisfy the threshold necessary for the breakeven field and lightning initiation....this is why I believe that lightning will continue to gain popularity in meteorological research in the coming years. AMS has taken notice by holding the 1st annual Meteorological Applications of Lightning Conference at the national meeting in San Diego back in January.