Report Offensive Message

But it's not pretty and it only works properly if your prevailing winds are from northerly directions (between 270 and 90).

For the line of data in cell A1, use this formula in cell B1:

=IF(A1 180,A1+360,A1)

For the average, use this formula:

=IF((AVERAGE(B1:B7))360,AVERAGE(B1:B7),(AVERAGE(B1:B7)-360))

Send me a PM and I can send you a sample of the spreadsheet.