Just a note for the Englishmen that have said they'd be getting attacked, you may and probably do still have viking ancestors. When William the Bastard(i.e. Duke of Normandy and King of England) took over, he and his people were only a few generations removed from the vikings that would sail up rivers and attack villages and monasteries.
Also, I would assume the raids would not be in the spring/summer. The vikings did a lot of farming and while I'm not sure, this may have been an important time for harvesting. Dunno, I forget much of what I learned when I was getting my degree. I may be wrong about 1200 year old farming methods.