Winter Sports Insurance
The slopes are pretty dangerous places and you really do need insurance. Your UK national health arrangements are not enough if things go wrong (especially in the USA).
Snow sports injury statistics
You have about a 2% chance of sustaining an injury during a week's skiing. Snowboarding is approximately twice as dangerous, with a 4% chance per week. These are fairly low figures, but high enough to mean insurance shouldn't be an optional extra for you, it should be something you absolutely insist on arranging.
Finding winter sports insurance
There are plenty of low cost comprehensive ski insurance packages and with the web, finding the best rates is child's play.
Wherever you go skiing and snowboarding, please do take out insurance before your holiday.