Rain in the Nether

When flying through unloaded chunks above the nether roof, I would see rain across my screen, regardless of whether or not it was raining in the over world. As far as I can tell this is completely visual, but is did tax my GPU more than usual (as rain general does on my lower-end computer).  This only happens when I am flying above y=180-250, though I couldn't find the exact y-level it starts at.