En dents de scie: An expression meaning up-and-down. It refers to the peaks and valleys on the serrated edge of a saw blade. (In English, we use the expression “roller-coaster” to the same effect.)
As seen in: « Les Canadiens devraient s’attendre à un hiver imprévisible, avec un temps en dents de scie. »
(Translation: “Canadians should expect an unpredictable winter, with temperatures going up and down.”)
