So I wasn't here during that time but prior to working at the obs, I did some work in forensic meteorology, so I like to look up obscure things like this from time to time. I can say that what you are remembering probably wasn't a tornado. Here is a link by NWS Grey, ME that lists all the tornadoes they have been verified in recent years: http://www.erh.noaa.gov/gyx/aware_thu.txt Although there were two reported and verified tornadoes that year, the timing of the NH one is too early and the South Paris one is a bit far. So I looked into the next thing I suspect it might be: straight line winds aka "Derechos". These strong winds can create damage similar to tornadoes and usually are mistaken for them. And by your description of the damage as well as the weather on the summit, I think this is what you are looking for. In this case, "The Syracuse Derecho of Labor Day 1998" coincides with the date your have in mind and there are pictures/video online of the suspected damage surprisingly in the area you mention. But you can turn to this page for more information about Derechos: http://www.spc.noaa.gov/misc/AbtDere...rechofacts.htm and the event: http://www.spc.noaa.gov/misc/AbtDere...p71998page.htm Or do a simple google search for more.
Hopefully this is what you were thinking of and looking for. If not, I can look at a few other ideas for you but if I had to bet, this would be the event you are thinking of. And to answer your question about record keeping, the observatory does not keep records of surrounding weather events like this, that would be more geared towards NWS or NCDC. We primarily keep records of weather on the summit or at our Mesonet sights around the summit in recent years. If you need those records, you can formally submit a request and we can possibly provide the weather for that given day if you would like.
Staff Meteorologist/Night Observer, KMWN (Mt Washington Obs., NH)