UPDATED forecast below (6:39pm) — When it comes to forecasting snow there tends to be two camps – those who want it to snow heavily and those who think “yeah right”.  

Forecasting snow in New Zealand is always hard – let’s spell out why: Compared to the body of water around us we are two small, mountainous, islands.  The sea around us is ‘warm’ compared to any blast of Antarctic air.  Inland parts of the South Island can have similar temperatures to inland parts of Canada – but coastal regions are much milder.  In places like Canada snow forecasts are usually all about timing – ie, the front will be at point A at 6pm then point B at 10pm.  In New Zealand snow falls at different altitudes – so while timing is part of it, the main focus for us as forecasters is ‘will the snow level be 200 metres – or 100 metres – or sea level?’.

So in large Canada, snow forecasts are quite easy – you’re following the front and timing it.

In New Zealand snow forecasts are harder because sea level snow is harder to forecast – especially when you’re not a large land mass but a couple of small islands surrounded by large bodies of water.  The final complicated part of the equation – we have mountains – some a few hundred metres high, others 4 kilometres high.  All of this works towards blocking – or increasing – snow amounts within each region. 

We make our forecasts based on various data (some you can see online – like our weather maps page – others private to us only). 

Taxpayers fund MetService to provide detailed snow watches and warnings – our predictions are independent and are simply a second opinion. We do not receive any tax or public funding but we do provide a free service to give a second opinion.

With that in mind – we decided to share with you an honest ‘behind the scenes’ opinion from our senior snow forecaster Aaron Wilkinson on the incoming snow: “…at the end of it all it might just be a nice spectacle for some city folk to see a little snow for a time, not going to affect many people in a serious way. In saying that the brief summary is worst affected areas may be North Canterbury especially inland. Ski fields should get a nice little top up“.

See WeatherWatch.co.nz’s snow forecast below…and of course make sure you’re up to date with any MetService snow warnings & watches for your area – for the most part this will just be a blast of very cold air…it’s mid-winter afterall.

– By Head weather analyst Philip Duncan – WeatherWatch.co.nz

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The details – in our view…(UPDATED 6:39pm Monday)

Southland: Gusty westerlies on Monday sees occasional snow flurries to 200m in the morning lowering to 50m or so later in the evening, perhaps near sea level. Amounts are not enough to worry about but 3 to 5cm could accumulate above 200m. On Tuesday the flow tends more southwest, the air is very cold, precipitation levels are quite low. So a few snow flurries to near sea level or perhaps sea level itself with 1 to 3cm possible but little more, once again not much to think about. On Wednesday a few further showers move through for a time around midday, the freezing level pops up a bit so snow flurries to 200m or perhaps 100m at the lowest.

Central Otago: Monday sees a few showers and snow flurries to 200m, 3 to 5cm possible at most. Nothing again till Tuesday late afternoon with snow flurries to low levels, won’t be much though, 1 to 3cm at the most. Again on Wednesday we have those few afternoon showers, 3cm or so possible to 200m.

Coastal Otago (includes Dunedin city): Nothing much really happens till midday Tuesday then shower activity clears overnight. Scattered wintry showers moving in around this time with a few snow flurries to near sea level. 1 to 3cm at most lower down with a max of 5cm above 200m. Showers pick up again on Wednesday then clear Thursday morning. A further 3-5cm above 200m, a few brief flurries possible to near sea level on Thursday morning before clearing.

South Canterbury. Nearly wouldn’t worry about it, due to the SW flow this part of Canterbury is going to be quite sheltered and see basically nothing – dry. Tuesday evening may see the briefest of flurries to sea level. Then again on Wednesday evening a few showers pass through that may deliver 1 to 2cm to 200m.

Mid Canterbury inland: The odd wintry shower from about Tuesday evening, continuing on and off through till Thursday night. The snow level basically staying above 200m but it may dip down to near or at sea level on Wednesday morning for a time. So the most one could expect, 10 to 15cm above 200m, 2 to 5cm to sea level, and more then likely these amounts will be towards the lower end of these ranges or possibly a tad lower.

Mid Canterbury coast: A bit more precipitation here. Shower timeline and snow levels very similar if not the same to inland Mid Canterbury but more precip overall. Since nothing near coastal mid Canterbury is above 200m we’ll only deal with stuff below 50 or 100m at most. So basically Tuesday evening and then Wednesday morning holds the best chance of snow to sea level with 5 to 10cm possible in theory.

North Canterbury inland: Similar timeline to Mid Canterbury in terms of when showers move in then eventually clear, similar precip levels to coastal Mid Canterbury but because we are higher in inland North Canterbury more areas will be affected. So above 300 / 200m we have the potential for upwards of 25cm of snow, now this is across the Tuesday evening through to Thursday night timeline, melt rates may dictate that some areas don’t actually get that much but it’s a potential outlook sort of thing. You never know some might even get a little more. Down to 100m 5 to 10cm looks possible on Tuesday evening / Wednesday morning, but then as those upper air temps lift on Wednesday afternoon precipitation at that 100m level will turn to rain / showers meaning it may not hang around for long and get washed away.

North Canterbury coast (includes Chch and Banks Peninsula): A bit more wind. The odd wintry shower may move in Tuesday late afternoon / evening but they don’t really push in till late morning on Wednesday. Showers finally move away on Friday morning. So over this whole period we could expect 15 to 20cm above 200m, remember this is a potential overall total, the end result may not exactly be this once this whole system has moved on. Tuesday evening / overnight and Wednesday morning has the sea level potential for chch city, only minor flurries expected now with a centimeter or two at the most, upper air temps lift on Wednesday around midday so shower activity will likely wash any snow away – meaning it won’t hang around for long. Banks Peninsula sticking more into the southwesterly airflow then Christchurch city may pick up a bit more snow to sea level during the Tuesday evening to Wednesday morning period with accumulations measuring anywhere from 1 to 5cm depending how lucky you are. The hill top road will likely have snow issues on Wednesday and Thursday so keeping up to date with roading conditions would be advisable if travelling over there.

Kaikoura coast / mountain ranges: Showers from Tuesday late afternoon / evening then hanging around on and off through till Friday morning, the odd straggler may not clear till Friday evening. Up to 20cm above 300m, 15cm to 200m then things drop off below that level, brief flurries may reach sea level on Wednesday morning but precipitation levels are low so may be nothing. The above applies to Marlborough too but we can cut precip levels a bit, 10 to 15cm to 400m, 5 to 10cm possible to 200m. Most of this would be occurring on the southern side of the Wairau Valley / Clifford Bay, north of there it gets very sheltered much like South Canterbury is in a southwesterly airflow. An initial burst moves through northern parts of Marlborough on Tuesday late afternoon / evening then clearing around midnight with some snow to 500m, lesser amounts to 300m then clearing, the rest of the time during this cold outbreak should remain dry.

Wellington: Showers move in around midday Tuesday. Finally clearing Friday night. Shower activity is fairly on and off and not very consistent so figures quoted are potential overall totals at the end of it all but it may end up being a little less due to melt rates etc. 15 to 20cm to 500m, 10cm to 200m. Overnight Wednesday and into Thursday morning  does look cold enough for some sea level snow now, accumulations will likely only be minor if anything but the potential is there for 1 to 3cm.

Wairarapa: Rain from Tuesday afternoon then easing to shower like activity overnight. Then on and off till early Saturday morning then clearing. 20 to 30cm above 600m, 10 to 15cm down to 200m. Wairarapa is a little more in the southwest flow so should in theory pick up more.

Hawkes Bay: While rain may be around for much of Tuesday upper air temps don’t drop till overnight but then shower activity drops off too, none the less. 10 to 15cm down to 600m, 10cm down to 400m and then minor amounts down to 300m. Air is coldest on Wednesday / Thursday but shower activity is fairly non existent so no snow if no precip. This make affect the Napier to Taupo Highway.

Central Plateau: Similar to Hawkes Bay, rain on Tuesday should see snow on the ski fields and hopefully a fair amount of it stays up there, but little to nothing lower down. On Wednesday upper air temperatures drop but then shower activity really drops off too. From Wednesday through to Friday expect sunny areas and periods of cloud, with cloud there may be a few wintry showers now and then bringing the odd snow flurry to 300m. Max possible totals, 3 to 5cm down to 300m with more then likely it being around 1 to 3cm. Melt rates and you know the rest may be not much if anything settling at that 300m level.

Sratford / Southern Taranaki. A similar outlook to the Central Plateau, so yes there may be a few flurries but it’s borderline, if any falls it won’t be much and will more than likely not settle.

– Detailed forecasts by Aaron Wilkinson, senior snow forecaster.

– WeatherWatch.co.nz