Custom Fiscal Calendar

Hi All

I'm hoping someone can help - I've tried a few variations of things I have found online, but I ahven't been able to adapt it.  And I think it needs to be done in Power Query if it can be done

Our company has a Fiscal Year calendar that starts on the Sunday after Thanksgiving as Day 1 of the Fiscal Year (December) and the following Saturday after Thanksgiving as Day 365 (or Day 366) as the last day of the fiscal year (November) - so the Fiscal Year start and end are moving targets each year.  Also, the Fiscal Months follow a pattern or 5 weeks (Dec), 4 weeks (Jan), 4 weeks (Feb), 5 weeks (March), 4 weeks, (April), 4 weeks (May), and down the line (5,4,4 - 5,4,4 - 5,4,4 - 5,4,4)

Any suggestions on how this can be accomplished?

Thanks in advance for any help