There must be hundreds of different stitches that can be used for the sky.  Try the Double Hungarian stitch the next time you are looking for a sky stitch.  It can be used on either 13 or 18 count canvases and goes fast especially if your sky is half of the canvas.  It’s also easy to compensate.  If your sky section happens to be a light blue with or without several different color changes try using Waterlilies from The Caron Collection in the color Ice (044).  It is an over dyed thread.  You will be happy with how it looks.