So I've browsed the vanilla 1.7.2 sources, looking for the rain code. It's a bit different than ours, but I think the numbers can be made more or less similar.
Basically, vanilla picks a number between 12,000 and 24,000 and uses that as the length of the rain (between 10 and 20 real-world minutes), and then picks a number between 12,000 and 180,000 (10 and 150 real-world minutes) and makes it sunny for this interval.
At the same time, it selects a number between 3,600 and 15,600 (3 and 13 real-world minutes) for thunder and between 12,000 and 180,000 (10 and 150 real-world minutes) for sunny. So vanilla can actually go from sunny directly to thunder and back; Cuberite can only go to thunder through rain.
Basically, vanilla picks a number between 12,000 and 24,000 and uses that as the length of the rain (between 10 and 20 real-world minutes), and then picks a number between 12,000 and 180,000 (10 and 150 real-world minutes) and makes it sunny for this interval.
At the same time, it selects a number between 3,600 and 15,600 (3 and 13 real-world minutes) for thunder and between 12,000 and 180,000 (10 and 150 real-world minutes) for sunny. So vanilla can actually go from sunny directly to thunder and back; Cuberite can only go to thunder through rain.