This is very clever!
Stephen Von Worley from the site Data Pointed has charted the last fifty years of rainfall in downtown San Francisco. He uses a line per rain year – that is, the period running from July 1st through the following June, centred on California’s wet winter months. The bars show the total rainfall received on either side of Valentine’s Day for each year. The years which finished wettest share one thing in common: none started out unusually dry. Click to see the graphic.