I grew up in rural Alabama. During the last year of high school (1976 fall-to-winter)...in the early afternoon (1 PM).....a bomb threat was called in.
We were 'herded' to a location by the football field (half a mile away). We were out there for 45 minutes before they admitted what was going on.
Temperature affect? Well...yeah, this was problem. It was probably 50 degrees, and we were lucky....no rain.
As far as I know....town cops led a 'search' (if you can consider it legit). I doubt if they knew what they were looking for.
At some point, about 25 minutes into this....we had this guy in my class...Gary, who was supposed to be in PE, and he'd come out in shorts/T-shirt. Gary reached a point where standing there was not practical, and he just took running toward the gym....to enter and get his jacket.
This Gary-moment was the most excitement of the 45 minutes.
Eventually, they decided to release school....lined up the buses, and gave us ten minutes to get inside....dump our books, and exit to the buses.
Now, if you were to ask me....who called the threat in? Well....there was this odd event at the bus area. The 20-year-old boyfriend of a 11th-grade girl....was parked and all ready to pick up his gal. It was impossible for him to have advance notice of the school letting out.
After this....for at least a week, we all talked about the event.