There has been a debate over the years re whether aircraft flying through clouds can trigger changes in the local weather. Researchers have now identified the circumstances when such may happen.
Water typically freezes at 32ºF or 0ºC. But, in the absence of dust or other small particulates (such as those described in prior posts), water in clouds can remain liquid at temperatures as low as -40ºC. In such a "supercooled state", even a slight disturbance can trigger freezing. Researchers have found that aircraft passing through clouds in such a state can trigger the formation of a sufficient number of ice crystals such that small snowstorms are triggered.
The fundamentals of such events can be triggered by the presence of a sufficent quantity of any type of small particle. Again, the somewhat unique conditions to cause this to happen are the absence of other small particulates and water in a supercooled state.
The study can be found at http://journals.ametsoc.org/doi/abs/10.1175/2009BAMS2905.1.