the "3 days of darkness" is mentioned by many prophets

[link to olrl.org]

It will be a bitterly cold winter night in the Northern hemisphere. (Presumably, a very cold summer night in Australia or, by contrast, a torrid night.) The wind will howl and roar. Lightning and thunderbolts of an unprecedented magnitude will strike the earth. The whole earth will shake, heavenly bodies will be disturbed – (this will be the beginning of the Three Days). Every Demon, every evil spirit will be released from hell and allowed to roam the earth. Terrifying apparitions will take place. Many will die from sheer fright. Fire will rain forth from the sky, all large cities will be destroyed, poisonous gases will fill the air, cries and lamentations everywhere. The unbelievers will burn in the open like withered grass. The entire earth will be afflicted; it will look like a huge graveyard.

As soon as you notice that bitterly cold night, go indoors, lock all doors and windows, pull down the blinds, stick adhesive paper on vents and around windows and doors. Do not answer calls from outside, do not look at the windows, or you will die on the spot: keep your eyes down to make sure you do not see the windows; the Wrath of God is mighty and no one should attempt to behold it. Light blessed wax candles; nothing else will burn, but the candles will not be extinguished once lit. Nothing will put them out in the houses of the faithful, but they will not burn in the houses of the godless. Sprinkle holy water about the house and especially in the vicinity of doors and windows: the devils fear holy water. Bless yourself with it and anoint your five senses with it: eyes, ears, nose, mouth, hands, feet, and forehead. Keep on hand a sufficient supply of drinking water and, if possible, food also (but you can live without food for three days.) Kneel down and pray incessantly with outstretched arms, or prostrate on the floor. Make acts of contrition, faith, hope, and charity. Above all say the Rosary and meditate on the Sorrowful mysteries.

Some people, especially children, will be taken up to Heaven beforehand to spare them the horror of these days. People caught outdoors will die instantly. Three-quarters of the human race will be exterminated, – more men than women. No one will escape the terror of these days.