Possible explanation -- forest fire smoke. Winds at flight levels around 10k were NNW 40-60, previous night heavy thunderstorms from Quebec moved south through Vermont and New Hampshire into MA.
I'm aware of some forest fires burning in northeast Ontario and central Quebec that could have been feeding into this region at the time mentioned. Possibly there were new fires started in northern New England by the lightning (severe storms were moving south across Vermont from about 01 to 03 UTC May 27).
Wind direction closer to surface was ENE from Atlantic, no smoke likely in those levels so people on ground unaware of problem.