I noticed the same thing when I was atop Cannon Mountain in late July. The foliage up there (4000 feet) was looking very "pre-fall." We're talking scrub trees, but they do have an annual color scheme to them, nothing like in the valleys, but the color scheme was definitely showing in late July.
This summer's weather at the Mount Washington summit has brought notable cold extremes -- accumulating snow in early July, and rime ice (freezing fog) just a couple of weeks ago. A chill at altitude is usually best shown (at our level) by the amount of hail we have in any given summer. To have hail from a thunderstorm, you have to have a low enough freezing level or it'll come down as cold raindrops. In a typical "hot summer" in New England, hail is sometimes not possible in a severe thunderstorm, due to freezing level being too high. The thunderstorm then takes its 'severe' criteria by having damaging wind (damaging wind and/or hail are what define a severe thunderstorm.)
This summer I have also noticed a great number of days with very low humidity and west (rather than south) air flow. On a couple of occasions this summer, the dewpoint fell to the upper 30s (F). That kind of air is more typical of fall.
Dry air brings chilly nights with warm days, as one might find in a desert (water content in the air slows the rate of heat loss at night.) Such a dry-air temperature scheme tells the trees it's fall. It is also true that they turn color when stressed. A few years ago one of my maples got damaged in a storm, and it was an early color-changer until it healed.
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