A severe thunderstorm warning has been issued for Christchurch this afternoon. 

“These thunderstorms are expected to be accompanied by very heavy rain and large hail,” MetService said in its warning. 

“Very heavy rain can cause surface and/or flash flooding about streams, gullies and urban areas, and make driving conditions extremely hazardous. 

“Large hail can cause significant damage to crops, orchards, vines, glasshouses and vehicles, and make driving conditions hazardous.” 

Meanwhile, residents in New Zealand’s southern most town Bluff were blanketed by a freak and intense hailstorm this morning that left much of the town white. 

One resident posted on Facebook that he was biking to “the Bluffs” when he “barely outran the storm”. 

“(I) just caught the edge of some crazy winds, got knocked down by some hail,” he said. 

“Just gunned it and made (it) through to the clear skies... Spotted a couple more funnels forming… just glad we dodged them all.” 

Truck driver Carl Kirkbeck told 1 News he noticed a dark cloud over Bluff while bringing new fish bins out to the factories. 

“Looking at Bluff, it was jet black. It was a black you cannot describe,” he said. 

Kirkbeck’s colleague warned him of a hailstorm in the area. 

“When we drove into it and saw it, it was like ‘holy smoke. Is it bloody snow or is it actually hail?’.” 

MetService meteorologist Matt Ford said there is a cold southwesterly flow affecting the South Island at the moment. 

“That would bring hail, heavy showers, and even some snow in some places, in parts of the southern South Island,” he said. 

Several alpine roads in the lower South Island saw a sprinkling of snow this morning, with road snowfall warnings issued for Arthur’s Pass, Milford Rd, Lindis Pass and Crown Rage Rd. 

“But the good thing is that this eases today and into tomorrow. There is some brighter weather on the way,” Ford said. 

Ford said hailstones form when cold air is very high up in the atmosphere, and warm air rises. 

“When it rises it cools and forms thunderstorms and hail clouds,” he said. 

“What you need are really strong updrafts and downdrafts within the clouds.” 

Ford said when the raindrops in clouds become heavy enough, they form hailstones. 

This story was originally published on the Herald, here