It was supposed to be a light dusting of snow, but it turned into the heaviest snowfall of the year, bringing parts of Dunedin city to a standstill.
MetService meteorologist Dan Corrigan said yesterday’s snowfall was much heavier than forecast, particularly in Dunedin’s hill suburbs.
Originally, the forecast was for snow showers around the city that were not expected to settle for long. But snow settled in the Octagon during the night and remained quite thick in the hill suburbs until late yesterday morning.
Mr Corrigan said many factors were at play when forecasting snow down to a certain level.
One was determining the broad-scale freezing level — the height at which moisture freezes — and another was the depth of the cells (clouds) that held moisture.
The more moisture there was in the clouds, the more snow it could produce, he said.
"Given the data we had, it looked like the most likely outcome was slightly less snow at slightly higher elevations like the hill suburbs of Dunedin.
"It turned out that the air from Antarctic origin was cold enough and the shower cells were deep enough to produce snow a little bit lower than we were initially forecasting.
"The snow level is kind of a knife-edge thing to forecast. A very small change in the atmospheric conditions can relate to a change in the snow level of a couple of hundred metres.
"It is a difficult thing to get on top of."
Mr Corrigan said that MetService meteorologists were now turning their focus to early next week, when there might be more snow.
However, it was still too early to say how heavy or how low it would fall, he said.
