A cold snap lining up to hit the South Island from Sunday into early next week has the potential to be as bad as last month's snowstorm.



Forecasters have been monitoring the development of the bitter southerly blast.



Computer guidance shows several pulses of Antarctic air are likely to flood across almost the entire country from Sunday.



Heavy snow to sea level is likely again in Canterbury and elsewhere in the South Island from Sunday afternoon through to Monday.



Snow showers are likely to continue on Tuesday and possibly on Wednesday.



Snow could stay on the ground for longer this time as it does not appear mild nor'westerly winds will follow the southerly outbreak.



MetService spokesman Dan Corbett said it looked like it would be an "exceptionally cold" outbreak.



Farmers were being warned now to prepare for the bad weather, with gale-force winds accompanying the snow in places, as it would have a significant impact on lambing.



It was still too early to know where the heaviest falls would be, but the storm looked like it would last longer than the July 25 storm, he said.



STACY SQUIRES SNOW FUN: Heavy snow in Christchurch on July 24 and 25 meant people were advised to stay inside and not to travel. Paige Manson, 16, left, and Manaaki Kerei, 17, made a quake-damage-inspired "Slow down snowman" in the red zone.