Is there any way we can opt to sort the messages within a thread in reverse-chronological order ?

This way, if you were away from the website for a week, you could read a thread starting from the beginning and then read the responses to it.

It's always weird to come here, start at the bottom of the page and then read & scroll up.

That's right, the (older) version of Ultimate Bulletin Board I'm using creates the pages statically, so it doesn't have many "real-time" options for changing the layout of the page. One benefit of the static pages is that it's easy for search engines (e.g., DCSki's own search engine, Google, etc.) to pick up the message forum posts and index them. At some point, I will probably upgrade to message forum software that uses a database, which would offer more options for layout (e.g., changing sort order on the fly). I don't tend to make major changes in the middle of the ski season, though -- I'm contemplating a major overhaul of DCSki next summer, and that would be the time when I would swap in a new bulletin board package.

I believe this is a limitation of the forum software (Ultimate Bulletin Board) rather than the actual setup/design by the website authors. Normally reverse order situation is changed when upgrading to newer forum software.