X-axis in a Stackeded Area Chart

[Entergy08]

I have 2 Stacked area charts.  One shows data from a date X and prior and the other is from date x and after.  What I am trying to see if I can make both charts have the same scaling so the before and after have the same look.  I would prefer one chart, but I have not been able to find a way to insert a horizontal line to represent a specific date.