How you to want to flag the spike ?
I did it recently as a dual axis graph - a line with a red dot when they exceed the 6 month rolling average. The line is your monthly data and the "exceed" calculation just returns a 1 or a 0 and then you graph that as well and make it a shape.
Let me know if you need more help and I can create it on Superstore for you
can u make it in superstore for me so i can see if it helps? Thanks!