I wish I ss'd it to prove the npc part, but I was showing another poster on bg who thought qufim shared lights with sky that that was a myth.
It's not so much that they share the same forecast, but they share the same cycle. It mimics RL in that light weather peaks around the solstaces, so you more or less have around 1 game week in each 90 game day rotation where it will pop close together, sometimes on back to back days....but more often it is every other day. When they see it is up for qufim, they run to their portals and hit the magian books to get the forecasts for sky.