Snow is expected to build up across parts of the lower South Island from Sunday morning, with a moderate chance of MetService upgrading its warnings.An orange heavy snow warning is in place for northern Southland and Otago, excluding coastal areas.MetService meteorologist Maddy Neal said the region could be in for some heavy accumulations of snow at some levels.With the warning going into effect from 6am Sunday until 6am Monday, Neal said there were no current "observations" of snowfall."As we progress through the day, the snow level is going to lower, which is why we have a warning out because people in some urban areas, including parts of Central Otago, Northern Southland and even potentially urban areas of Dunedin may see some snow later in the day as that snow level lowers down to possibly 200 metres in places."She said the chance of the orange warning being upgraded to a red warning was now moderate."It's not a red warning, but we could expect potentially some changes as we go through the day [on Sunday]."Neal also added there was a chance that snow accumulation could reach one metre in areas above 800m.MetService had also issued road snowfall warnings for Haast Pass (SH6), Lindis Pass (SH8), Crown Range Road, Milford Road (SH94) and Dunedin to Waitati Highway (SH1).The warning for Milford Road is set to lift at 9am Sunday morning, with warnings for Lindis Pass and Crown Range Road to go until Sunday night. Haast Pass and Dunedin to Waitati Highway will have a warning until Monday morning.Neal said they had expected rain to turn to snow near the summit of Milford Road on Saturday night and Sunday morning with a forecast of two to five centimetres of snow with lesser amounts down to 800 metres.For other roads under warnings, snow was expected to accumulate throughout the day and night and Neal urged drivers to be cautious especially with the start of the school holidays."We just want to make sure that people are driving to the conditions and thinking about changing their travel plans if they're going to be experiencing disruptions from snow."A heavy rain watch was also in place for Mainland Southland (not including northern Southland above 400 metres) until 11pm on Sunday.Fiordland north of Doubtful Sound and west of the main divide is also under a strong wind watch until 9pm Monday.