Snow is falling in some parts of the South Island, rain for others – meanwhile the North Island is fairly dry (for now). Currently we have a northerly airflow covering a large portion of the country, but a southerly airflow is undercutting this on the east coast of the South Island, up through to Canterbury. This is called a ‘warm advection snow fall event’.

Below is a detailed forecast for snow tonight across some parts of the South Island produced by WeatherWatch.co.nz.

Southland: Currently it’s actually looking mainly dry, this whole event shifted a little northwards. It’s mainly cloudy now with easterly winds, overnight some rain moves back in with snow to 300m. Areas of rain continue overnight then clear around midday friday at which point snow will have lifted above 800m. 5cm possible to 300m, 10 to 15cm down to 800m sort’ve thing then staggering amounts in between.

Central Otago: Rain eases later this evening to the odd shower overnight which clears midday Friday. Snow to 300 or perhaps 200m lifting to 700m by midday Friday at which point showers clear. So 15cm or so possible to 300 or perhaps 200m. Potentially 20 to 30cm above 700m.

Coastal Otago: Patchy rain or showers through till midday tomorrow then clearing. The air looks colder here nearer the coast but precipitation amounts are down. Snow flurries to low levels, perhaps even as low as 50m, then lifting Friday to 700m by midday at which point showers clear. So, 5 to 10cm possible to low levels, 10 to 15cm above 700m from now on.

North Otago: A little different as rain and snow amounts are greater inland / higher up. Areas of rain from now ease to patchy showers overnight which clear midday tomorrow. 10 to 15cm down to low levels (yes perhaps even 50m / near sea level). 15 to 20cm above 700m all going well once things clear Friday.

South Canterbury: Rain, fairly persistent and not easing till overnight / dawn tomorrow at which point there is only a few patchy showers finally clearing around midday. Snow to low levels (100 perhaps even 50m) then lifting to 700m Friday morning. Snow is likely to be heavy, 20 to 25cm possible to low levels, there is a chance this could be slightly higher in terms of the amount of snow. 30 to 35cm to 700m, perhaps even up to 40cm.

Mid Canterbury: Currently snow is falling to about 100m in some areas – but it’s patchy. We have a fair amount of precipitation / rain falling for the rest of tonight and not easing till overnight / dawn tomorrow then the odd patchy shower clears Friday morning. So snow to low levels 100 / 200m then lifting above 700m overnight / around dawn Friday then clearing Friday morning. 20 to 30cm to low levels, 30 to 60 above 500m. And yes perhaps up to the miracle 1 meter mark at really high altitudes (above 1000m).  As we get closer to the coast in Mid Canterbury precipitation levels drop off. So it’ll look more like this for coastal Mid Canterbury, 15 to 20cm down to 200m possible, lesser amounts down to 100m i.e. 5 to 10cm, snow may even fall to 50m if you’re lucky but by then it’s likely just flurries and not settling.

North Canterbury (Christchurch mainly): Rain from now continuing through the night and clearing early Friday morning. Snow to 300 or 200m currently and lowering to 100m this evening, perhaps a chance flurries could make it to 50m but they will most likely not settle. As of 6:30pm it was just 2 degrees and raining – and has been that way for the past couple of hours. So, 15 to 20cm above 300m, 10 to 15cm down to 200m, 5 to 10cm possible to 100m then any lower then that and it’s going to be a slush. These are a best attempt to show what could happen. Amounts could be more as you head into the foothills behind chch (towards the mountains), so add 5 to 10cm to the amounts above.

Further into North Canterbury (Waipara / Amberley northwards) it’s a similar picture to Chch but expect snow levels to be 100 to 200m higher overall. Then Marlborough 100 to 200m higher again, perhaps even 300m higher so that could mean Marlborough snow will stick above 800m which is more then likely.

– WeatherWatch.co.nz detailed forecasts

– By weather analyst Aaron Wilkinson