As you probably know, the east coast of the U.S. has been getting pretty cold lately, and I just heard of the fimbulwinter. This prompts me to ask: what happens in during the fimbulwinter? What are its signs?
First, there is a winter called the Fimbul-winter, when snow drives from all quarters, the frosts are so severe, the winds so keen and piercing, that there is no joy in the sun. There are three such winters in succession, without any intervening summer. But before these there are three other winters, during which great wars rage over all the world. Brothers slay each other for the sake of gain, and no one spares his father or mother in that manslaughter and adultery. Thus says the Vala's Prophecy: Brothers will fight together And become each other's bane; Sisters' children Their sib shall spoil. Hard is the world, Sensual sins grow huge. There are ax-ages, sword-ages--- Shields are cleft in twain,--- There are wind-ages, wolf-ages, Ere the world falls dead. Then happens what will seem a great miracle, that the wolf devours the sun, and this will seem a great loss. The other wolf will devour the moon, and this too will cause great mischief. The stars shall be hurled from heaven. Then it shall come to pass that the earth and the mountains will shake so violently that trees will be torn up by the roots, the mountains will topple down, and all bonds and fetters will be broken and snapped.
from Gylfaginning. The Vala is a seer, and Fimbul means great.
The Fimbulwinter might very well be a mythological take on certain historical facts and there is evidence that might be at least considered in that direction. Bo Gräslund, professor of archaeology at Uppsala University, Sweden has written an article on the subject connecting the Fimbulwinter to, among other possibilities, climatic changes due to vulcanic activity around 536 CE. The event is put forward as a possible sollution to an old problem in Swedish archaeology concerning dramatic changes in economic, ecological and demographic patterns around 500 CE. This might not be the answer you are looking for since you seem more interested in the prophetic element of the myth.
Bo Gräslunds article (I am sorry, but I can't locate it in English right now) Fimbulvintern, Ragnarök och Klimatkris PDF-Swedish
An article by Daniel Löwenborg in English further exploring the ideas: An Iron Age Shock Doctrine PDF
Questions about Fimbulwinter belong in /r/mythology. History is not looking for signs of future mythical events.