https://www.dot.nh.gov/news-and-medi...tch-state-park
The road closure is due to recent floods. I have not seen a detailed assessment of the damage. Cars definitely can not make it the AT trailhead but if the usual spots along the highway washed out, pedestrian access may also not be possible. Pure speculation on my part is that access from the south, although longer may be possible at some point as there are homes north of the washed out Bemis bridge.