In the 2050s, the supercell thunderstorms (seemingly impossibly) gained ferocity and frequency. Eventually, there came a time where they were so frequent they blended together and never stopped. The Great Storm had arrived.
No one could pinpoint exactly when the Great Storm began or knows how long it lasted, although its estimated to be at least a generation. As for the "end of history," later historians never recovered anything beyond 2063. This was declared the official end of the AD timeline.
Like the creep before it, the Great Storm effectively reset society. Whereas the creep spared much of humanity and left the structures in tact, the Great Storm claimed billions of lives and destroyed most of civilization. Even for the hundreds of thousands who lived through it, few came out with their sanity.
At the end of the storm, the landscape was covered with roaming packs of storm-crazed maniacs who formed animalistic tribes and could no longer be considered men.