Is this pure RNG, or is there a specific day, player condition (like spawning an S-Rank), etc. to get this weather?

I've apparently traveled forward in time from 2 years ago trying to finish my ARR sight log, and this one continues to elude me.

Also, according to this site, http://vistas.explorexiv.com, the condition should hit in 7 hours. Which is also when the server is going down for maintenance. Does that mean weather resets too?