What if a series of storms like the one in 1588 occurred in 1066, forcing the Norman fleet off-course, east and north around England?
Scenario 1: William's fleet lands in Yorkshire
Scenario 2: William's fleet lands in Orkney or the Faroes.
Scenario 3: William has to round Great Britain entirely and arrives in western Scotland (perhaps in the lordship of the isles), with severe attrition.