Hokitika has just had its wettest May since 1866.
After a mild, though very wet, May, the first proper snow is forecast for tomorrow.
"A cold snap kicks in later this week, and continues through next week," the MetService said.
People travelling to or from Christchurch this weekend should check for snow alerts, with early signs it could also fall in the hills of Canterbury and Otago.
So far the mountains are fairly bereft of snow.
Hokitika weather observer Mark Crompton said as well as being the wettest May there since the town was founded, it was also one of the warmest.
For the month, Hokitika measured 609mm of rain, more than double the May average of 271mm.
The figure blitzed the previous wettest May — 579mm in 2016, and before that 1877 with 561mm.
Mr Crompton said with so much rain and cloud, the night temperatures had stayed warm so the mean temperature was well up. On May 1 it got to 23degC with an average of 14.1degC for the month.
"It’s four or five degrees above average."
Two more days of rain are forecast before the cold snap later this weekend. Skies should then clear.
"Saturday is a lay day. If you see a bright object in the sky, it’s not a UFO!
"On Sunday, more rain, a depression brews up.
"It will be followed by a cold southerly or southeasterly, later Sunday and Monday.
"It could dump snow in Otago and Canterbury which would be very welcome — the skifields are bare."
The MetService said it was expecting a light dusting of snow before the front even arrived, from 9am today on Arthur’s Pass, but little if any will settle.
