From memory:
LBT 1: Twice: when littlefoots egg is about to hatch and when littlefoot's mom dies
LBT 2 and 3: Can't remember it raining in either film (haven't seen them for years and years) but from info I've found on other sources once apiece
LBT 4: From memory (I haven't seen this movie in years) and screenshots I found online it did rain in the land of mists on an occasion.
LB 5: Only in the introduction...does that count?
LBT 6: ONCE briefly
LBT 7: Yes, when Pterano, Sierra and Rinkus land on the cliff and Pterano sings his song, and as the kids take shelter in a cave.
LBT 8: None, just snow.
LBT 9: A whopping 3 times---the only film besides the original to have rain twice unless it happened twice in 2-4...can't remember
LBT 10-12: 0
lbt 13: once
I basically saw a post from a long time ago about this, so I'm mostly basing it off of that, but am I right?