The bodies are formed by precipitation. Big globs of water form the bodies, and will gain the flesh after initial formation.
I see. This does offer routes to make things interesting, like why and how would those water droplets condense into human bodies that release death miasma? Some food for thought that may or may not aid in brainstorming.
The 1300 BC thing might be a bit reduntant. Il remove it or replace it with something relevant.
If you would like to denote some "origin" (factoring in that the bodies are merely condensed water droplets), I would suggest clothes or skin colour or tattoos (for certain cultures that use them to denote maturity etc.).
Slovakia was the starting point for a famous urban legend where it rained corpses one night. The traveling to other areas is original as storms travel. (Also it is on purpose, the phenomnom is a sentient entity.)
I see. It is good and all to reference an urban legend and its origin (I do that myself), and equally good to consider the reality of weather phenomenon. But if you intend for the storms to be sentient, do consider how you intend to show that to readers in your article. If it is sentient, what does it do with its action of dropping corpses that release death miasma?