The unseasonable weather saw cars in ditches and on their roofs and motorcycles strewn across the carriageways of the A27, one of the main routes to the city.
Weathermen said the average temperature for April was generally 10C or 11C, but on Sunday, April 6, 2008, it barely touched 3C.
West Sussex County Council admitted it was caught out by the bad weather and failed to grit the roads. A spokesman said: "The gritters did not go out Saturday because the official forecast information we received was temperatures would not fall below zero.
"Had there been a prediction of freezing temperatures, they would have gone out. The gritters and ploughs were mobilised first thing Sunday morning as soon as it became clear snow was settling."