Aucklanders learnt a new word yesterday: “graupel”. Halfway between snow and sleet, it forms when very cold droplets of water hit snowflakes to form a “rime”. Because the white stuff that hit Auckland yesterday didn’t really feel like snow. It was harder than sleet but softer than hail – and it came at you sideways. All Aucklanders knew was that it was very cold and there was something that bore a close resemblance to snow piling up on the ground. But since it’s been almost 80 years since snow fell in New Zealand’s largest city, it was perhaps not surprising that the initial reports suggested it wasn’t quite the real thing.
Even the scientists struggled to believe it was snow, not graupel. “The sleet that we’re receiving could look a lot like snow, could actually well be snow flakes drifting down horizontally,” says Catherine Griffiths, senior climate scientist at the National Institute of Water and Atmospheric Research. “If people think it was snow flurries then it probably was.”
Auckland, you see, doesn’t get very cold – there hasn’t been snow here since 1939, although there were reports of a flurry (possibly graupel; no one is entirely sure) in 1976. Auckland is better known for its rain in winter, which is constant, with locals beginning to comment about the cold when the mercury falls anywhere below 8C.
But this winter, after a mild start, has been a bitterly cold one for New Zealand and, on Sunday, a cold front came blasting up from Antarctica. The temperature dropped to zero from Bluff in the south to Auckland in the north, and most of the country was blanketed with snow on Sunday and Monday. In the South Island – where it does snow most winters – flights were cancelled and major highways closed, stranding travellers and closing businesses.
The technical reason? That’s another vocabulary lesson. Metservice ambassador Bob McDavitt – who bears a close resemblance to Father Christmas – explains that the snow was caused by a weakening in the “polar vortex”, a dome of cold air over Antarctica. “Occasionally,” he says, “that dome, like a dam, has cracks in its wall and cold air spreads out.”
Aucklanders are just hoping the dam doesn’t burst for another 80 years.