Boot to Windows once from Grub then back to Ubuntu on next boot

From Ubuntu you can call grub-reboot

$ grub-reboot --help
Usage: /usr/sbin/grub-reboot [OPTION] entry
Set the default boot entry for GRUB, for the next boot only.

  -h, --help              print this message and exit
  -v, --version           print the version information and exit
  --root-directory=DIR    expect GRUB images under the directory DIR
                          instead of the root directory

ENTRY is a number or a menu item title.

Report bugs to <[email protected]>.
$ grub-reboot 12

to boot to Grub option 12 once on the next boot, after which it will revert back to the default.

The first entry will be 0. Names, however, are probably safer to use, as the grub menulist occasionally adds new items when you update your kernel.