The answer is somewhat complicated. Try to stay with me on this, okay?
For most people, the hamstrings are weaker than the quads. While stretching helps relieve muscle knots, it also temporarily makes the muscle slightly weaker. Sports Med. experts have recently discovered the static stretching before an athletic activity may not be that effective. The reason: By slightly weakening a muscle that is already somewhat weaker than its protagonist, the quads, it has to work harder than it should.
Still with me? Hang in there, I promise I'll get to a solution!
Another possible reason for the tight hamstrings is tight hip flexors. There is this quirky little factor called "reciprocal inhibition." In plain english, this means that if the hip flexors are tight, its synergistic muscles, the glutes, are weak.
So how does this effect the hamstrings? If the glutes, due to tight, restrictive hip flexors are not playing their part, the hamstrings have to do all of the work. But wait, the hamstrings are already not that strong. Now they have to do everything! UNFAIR! They are sayiing "OUCH, this is too hard.
Now for some solutions. At ESA, people enjoyed working on the foam rollers using a technique called myofascial self release. (do a serch, lots of stuff on this in this forum) Basically, it can be done either before or after skiing. Why? Because it's like massage. It loosens up the muscle lesions, without excessively increasing muscle length.
Hope this helps!