WeatherWhys for March 20,2014 from accuweather.com

At the moment spring begins, the sun is directly over the equator. In the weeks that follow, the most direct rays of the sun will migrate northward until reaching the Tropic of Cancer on the first day of summer in June. The apparent south to north migration of the sun's rays is caused by the tilt of the Earth's axis and the movement of the Earth around the sun.