Easy -- close as "too localized", but do not delete. There's nothing wrong with keeping these forever -- they are not bad for the site per se, just not very useful any longer. Also, all posters get to keep their reputation, and could repeatedly reap rep from them. No need to lock the question, AFAIR questions closed by mods cannot be reopened by the unwashed power user masses.
In this way, future visitors will still be able to get some useful information, if the event is recurrent, but at the same time, will be reminded that this question is possibly out of date and what is written may not be correct any longer.