I don't think it had to do with the temp outside, since most hot glue guns reach 300 degrees or so. Might have to use more glue. I know mine don't hold well when I don't use enough glue. I had to find that happy medium. Try using more glue, make sure your clips are warm when you put the glue on. I put my clips and spreading tool on a heating pad while I line the clips. HTH.