It's a uniform-sum distribution aka
Irwin-Hall distirbution with the caveat that it won't skip more than twice (stops at n=3).
For example,
this is what it looks like after 2 skips.
Stormfeather works the same way but with a max of 3 possible skips.
Probability of skipping seems to be roughly 50% based on my sample of ~100 spawns but I'd be interested if someone actually has hard numbers for this.