Then I spent around a month on and off just going for Chirpnado. I started the game around early July and unlocked every achievement except Chirpnado by mid August. According to TA it only took me 133 hours but I know for certain that it took longer than that. I probably spent maybe close to 100 hours for everything but the Chirpnado, then another 150 or so hours just for the Chirpnado. So, after about 250ish hours I've finally gotten done with the game and got the 100%. turn on random disaster and play the game, and it will eventually show up)** if you don't have any population in your city) Good luck to those who are lucky enough to see this.
as most pc players used the dev tools to hack the achievement. and there is very little information about this. you could get it in 1 hour or 1000 hours. The ending statement on this achievement. there has been reports of it as little as 5,000 population.
that it has a 0.40% chance to show up on your map ( scenario or normal game play ). Now the issue with this special disaster is. there is no evidence on the frequency effecting it, but i keep it maxed out. You are required to have " Use random disasters" enabled in your options. it's a blue Tornado with lots of blue birds flying around it, it upgrades everything in its path.
I hope this helps anyone trying to figure it out, but this is an easter egg.