Aircraft, radar, and surface observations were used to study the relationship between precipitation development and the onset of electrification in thunderstorms which formed near or over the Magdalena Mountains of New Mexico. The study included storms which were electrically active as well as ones in which no electrical enhancement was observed. Electric fields inside these clouds showed negligible enhancement and did not exceed 1 kV m-1 until reflectivities at 6 km above mean sea level (msl) (about -10¿C) exceeded approximately 40 dBZ and cloud tops and cloud tops exceeded 8 km. The onset of electrification occurred during or immediately after convective growth within the cloud. ¿ American Geophysical Union 1989