We always knew there was a risk, but we chose to ignore it.
There are always warnings, but only a single low-level official recognizes them.
There is one, and only one, scientist available to help identify the disaster and come up with a way to mitigate it. The lack of available scientists is made up for by the fact that the one who is around is a hot woman.
90% of the featured characters over the age of 40 will die tragically and heroically. The other 10% (usually Grandpa) will be rescued heroically.
A family will always be separated from each other (usually because mom and dad are divorced but sometimes because one of them is traveling). The parent who has the kids when the disaster happens will need rescuing by the other parent.
Disaster movies teach parents to stay together, 24/7. Never know when you’re gonna be needed!
The police, military and any other authority figures will be, at best, utterly ineffective at dealing with the disaster, and at worst, will use it as an excuse to become evil and corrupt.
But the one ordinary citizen who dares will be able to fix things better than all these authorities ever could, if he can manage a steely look of grim determination.
Close the volcano/beach/killbot factory during peak tourist season? You must be mad doctor/professor/handsome geologist/small town sheriff!
In the Day after tomorrow, the vice president is warned about a possible global catastrophe and he ignores it as is customary to the cliche. The problem is that he was warned only days before the catastrophe occurred. Even if he wanted to do something about it, it was already too late. Yet the movie makes him the villain. The vice president even makes a passionate speech about how wrong he was at the end of the movie. WTF!
The bad news is that in the future the machines will kill off almost all of humanity. The good news is that all the women left alive will be very very beautiful.
The people who follow the general/government scientist/ploitician will die. The people who follow the little kid/rogue scientist (especially the hot woman rogue scientist) will live.
Martians who say they “come in peace” are lying. Better to shoot them down before they land.
Find a mysterious old Native American shaman - he’s the only one who actually knows what you are dealing with. Extra points if his hot granddaughter is a highly-educated doctor or scientist and has rejected the old wisdom.