Water vapor does not rise as H2O compound but is decomposed by UV rays (photolysis) into H2 and O (single gaseous bodies). http://pdf.lu/zui0/
It is by compression due to rising and descending air currents (opposition of two mechanical forces) and at a favorable rate, hydrogen and oxygen combine in an explosive chemical reaction (synthesis: water). The condensation comes afterwards.
You see that everything is explained, from this explosion, one understands:
"Lightning + thunder + rain = one operation"