wingslevel - 12:29 am on Jul 2, 2012 (gmt 0)

But we can eliminate soccer tournaments, weather, holidays etc., by using analytics. If organic google referrals are normally 45% of your total traffic, but they are at 30%, likely something has happened to your rankings.

I think you also have to look carefully at the quality of the incoming google referrals - if you see goal conversion that varies significantly from historic levels, then you may be receiving lower quality traffic.