I am currently doing my IMC rating, so a lot of time spent working out drift corrected headings etc. Over the last few weeks, I have found the Metoffice forecast wind charts (Form F214) to be significantly more accurate than the winds aloft shown in Skydemon (where I would normally set a precise take-off time). What is the souce for winds aloft in Skydemon?

I was comparing the winds in SD against F214 this weekend and there was a considerable (20kts +) difference @ 3000'

Has any work been done to verify if GFS is more or less accurate than Met Ofice forcasts for the current day?