The second of three skirt drafts, I leaned about in the French Pattern Drafting/Moulage class I took from Lynda Maynard.
To create a flared skirt from a sloper. This example shows a back sloper. The changes are the same for both front and back.
Sixth, i. Cut a piece of tissue that would fill in behind the newly opened part of the skirt pattern with paper. This is the insertion. Then add another 1/4" to the insertion.
ii. Create an extension that is the same size as the original insertion. Tape your insertion and extension onto the back of your pattern.
Seventh - Make a nice new pattern piece with no tape. You may want to go ahead and add seam allowances to the new pattern. Since I draft my patterns from my sloper, it doesn't have seam allowances already. A 1" seam allowance is great, the first time you draft a pattern. It gives you a lot of wiggle room.
Don't forget to date your new pattern pieces. You'll be glad you did.