(note: excerpt lightly edited, from Pavel Vaptsarov's Hail Suppression Website)
The hail suppression project in Bulgaria started with protection of about 250 000 ha (One hectare equals 2.471 acres, from Conversion Facts and Formulas) and since 1987 the protected area reaches 1 500 000 ha.
In the beginning Russian rockets were used like “PGI”, “Oblako”, “Alazan” , which carried an active reagent based on lead iodide, and a Georgian methodology for hail clouds identification and their seeding.
[In] 1986 a Bulgarian methodology for identification and seeding of hail clouds [was] introduced, based on physics-statistic methods.
[In] 1994 the active reagent in the available “Alazan” rockets [was] replaced with silver iodide and the implementation of the first model for reagent diffusion in the atmosphere [was started].
[In] 1999 the manufacture of a Bulgarian anti-hail rocket started; [and] the rocket carried the upgraded version of the active reagent, based on silver iodide.
The software [that] is used, translates the location of all objects to the radar coordinate system and selects the most suitable launching site for cloud seeding according [to the] particular meteorological conditions in that day. Also the area of seeding and the method is made more precise.