CHIPPEWA FALLS, Wis. (AP) _ A 12-year-old boy suffocated after the snow fort he was playing in collapsed when a plow pushed more snow onto it from a nearby road, authorities said Friday.

Eric James Jensen of Cadott had been missing for nearly 18 hours before his father and a family friend found his body Thanksgiving morning a few feet under the snow.

An autopsy conducted at St. Joseph's Hospital in Chippewa Falls on Friday concluded the boy died of asphyxiation.

''The awful part is that he was in sight of the house,'' said the boy's mother, Bessie Jensen. ''I could have looked out the window and seen where he had been.''

Eric left his rural northwestern Wisconsin home at about 2 p.m. Wednesday to play in the yard, and his family became worried when he failed to return a couple of hours later. A ground and aerial search was launched.

A Chippewa County Highway Department snow grader operator told authorities he had plowed the road near the Jensens' house at about 4 p.m. Wednesday.

There was no way the plow operator could have seen the boy, who had tunneled into a snowbank at the side of the road to make his fort, said Douglas Ellis, a Chippewa County Sheriff's Department investigator.