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Confusion remains over predicted snow storm

MetService has gone all out predicting what they call a “significant” snow storm for the country this Sunday and Monday – but confusion remains over just how low it will fall with snow not predicted by them in any of their main centre forecasts apart from Queenstown.

“According to MetService, this polar outbreak is likely to bring gale force winds, as well as snow showers to very low levels, to southern and eastern parts of both islands on Sunday or Monday” they said in a press release yesterday.

In their severe weather outlook they also posted “moderate confidence” of snow warnings being issued across two thirds of the South Island and a significant chunk of the lower North Island, one of the more widespread snow predictions they’ve made.

However the word “snow” isn’t actually used in any of their forecasts for Invercargill, Dunedin, Christchurch or Wellington, meaning some confusion on just how much snow will fall and to how low.

Computer models are struggling with the snowy forecast and forecasters say there is still too much confusion to be certain of heavy snow to low levels.  “Some models have a high moving in, others have the complete opposite with a low off the east coast driving in bitterly cold south easterlies and snow to sea level” says head weather analyst Philip Duncan.

He says the ingredients are definitely there for a snow event but there are a couple of factors stacked against it.  “Two of the models we rely on predict a high moving in, which would push the snow storm out over the Chatham Islands instead.  Another model, perhaps one that is considered more reliable, is predicting snow to very low levels.  As you can see it’s quite a tricky forecast”.

Weather anayst Richard Green says the computer models are flip flopping on the chance of snow showers for eastern parts of NZ late in the weekend and on Monday and he says it seems that much of the moisture will be east of New Zealand “however the cold southerlies should still feel very cold and some showers may have a wintry mix”.

“We’re keeping an eye on this one, other forecasters have predicted significant snowfalls and at one point yesterday it looked likely but today it’s a slightly more marginal call”.

Snow storms in New Zealand can be very tricky to predict too far in advance and while it’s fairly common for computer models to disagree on weather forecasts it is a little unusual to see such huge differences between the international models over something so potentially significant. predicts a cold change on Sunday and Monday which could see snow to low levels but confidence remains low at this stage of anything too severe.

We will be monitoring this very closely and will bring you updates as our confidence increases or decreases of this snow event.


Andrew on 10/08/2011 10:08pm

Metservice could well be forecasting widespread heavy snow to 400-500 metres which would then fit in with the criteria for a heavy snow warning. As our main centres are not at 400-500 metres the forecast would then not include snow. Easy really.
It looks like a widespread but slow event to me, with widespread snow from Dunedin north to the Central Plateau but not to sea-level. The air just doesn’t look polar enough to me. It’s probably a two day event so will have farmers bleating.
A decent but typical late winter event. Try that for a commentators curse.

Guest on 10/08/2011 10:56pm

If you check the metservice mountain forecast – specifically the freezing level – for sunday/monday, they are saying it will be 500 metres for much of the south island and 700 metres in the lower north island.

Given that snow normally falls only 2-300 metres below the freezing level, that would suggest snow to 200 metres in the south island and 400 metres in the lower north island. That is low enough to cause major problems in most places – particularly if the amounts are significant – but high enough to miss all the main centres except Queenstown.

WW Forecast Team on 10/08/2011 10:58pm

It’s the use of the term "very low levels" by them that seems to be creating the confusion.

– WW

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