Shin splints

You are probably experiencing "shin bang". I used to have major issues with shin bang. Usually, it can arise from a number of issues. Skiing technique is probably the biggest cause. If you lean back in your boots when you ski, or are constantly landing jumps/rails backseat, you strain the tendons in your shin as you lean back in your boots. Then, when you lean forward, you feel that familiar, agonizing pain pinpointed on your upper shin. Improving your skiing technique will GREATLY reduce your shin bang. Secondly, its very important to have proper fitting boots. Reducing the amount of "slop" in your boot will keep everything locked in and help the movement that causes shin bang.

For me, it was a combination of improved skiing technique, getting stronger as a I got older, and becoming more informed about boot fitting that helped to kick my shin bang issue. However, I still get it pretty bad after a day or riding a big jump line.

That has been my experience anyway, I'm not sure if that helps at all.
There are some good threads about this, just google "shin bang".

You get shin splints from overuse and stress to your muscles in your shins (probably old running injuries). The muscles essentially get micro tears along a membrane on your shin bones. A way to help this is compression so if you get boots that fit well they will provide compression to the area and help reduce some of the pain.