In a notification released late Wednesday night, school officials said they were dealing with an "emergency situation" and asked students, staff and community members to stay away from the school on Thursday.
The King County sheriff's office is investigating an online post claiming to be from a Skyline student. In the post, which included a photo of a gun, the student says he's going to take his father's gun to school and "open fire on the people in the commons in the morning until I am either taken down by our school's police officer, or until I run out of mags."
The post was circulated around social media sites on Wednesday and was reported to police.
Deputies so far don't know who wrote the post or if it's a legitimate threat, according to King County sheriff's Sgt. Cindi West.
In Wednesday's email to parents, the school district apologized for the late notification, but said "student and staff safety is our top concern."