Why was the start to spring 2013 so cold?

‘Distribution of temperature anomalies over the UK from the climatology for 1981-2010. : This link opens in a new window

‘March 2013 was the second coldest March in the UK record since 1910, and was associated with a negative phase of the North Atlantic Oscillation. A number of potential drivers may predispose the climate system to a state which accounts for these conditions…’

Article from the Met Office