May 19th dawned as bright and clear as usual, except there appeared to be a haze to the southwest.The haze grew darker and soon the whole sky was covered with a thick cloud that was traveling northeast rapidly. It reached the canadian border by midmorning. Meanwhile, the eastern part of New York, Maine New Hampshire, Rhode Island, Massachusetts, and Connecticut were becoming darker.
more from Williamstown magazine via FR (NSFW). and there is a discussion if it was a forest fire or a volcano.
I'd say a forest fire, since no nearby volcanos.