The cold blast has already started to work its way up the lower South Island and will today head north. The data we rely on has been doing what it usually does just before a storm – flip flopping – as computers struggle to work out exactly what is going on.
So at times like this it’s best to take a step back and just look at the entire set up. Polar air, directly from Antarctica, is moving up New Zealand – with snow and severe gales, hail and showers, sunny spells in the mix too.
The flip flopping by the models has been fairly minimal but still very frustrating – why? Because it’s the temperatures that are fluctuating the most. With most storms this is irrelevant – but when snow is possible in our main centres we have to narrow in on temperatures.
Think of this way – for water to freeze the air must be zero or below. But what if the air is hovering between -2 and +2? Then it comes down to how much time is spent below zero. The snow forecasts for coastal NZ are similar – we have high confidence of snow down to 100m – but down to sea level will need perfect conditions. If the temperature scales tip down a couple degrees – we’ll have snow, heavy and settling. If it tips up a couple degrees, it may only be a rain/snow mix. It’s rare in weather forecasting in NZ that we have to be this specific – so focused on a 1 or 2 degree margin of error – but that’s the nature of snow forecasting to sea level here, especially when so many New Zealanders tell us they want it to snow in their town or city.
The storm is running about 24 hours behind schedule from our earlier predictions on Monday. We now expect the bulk of the severe weather to be across Friday and now pushing into Saturday for the North Island, but clearing as the day goes on.
We’ll do our best to keep you up to date with the very latest over the next few days.
If you’re a farmer inland across Canterbury, Otago and Southland – snow amounts may be heavy across Thursday PM and Friday AM. One sector that will be hoping we are wrong with our predictions will be the farming one – wind chills and heavy snow could lead to stock losses, but as farmers have pointed out – at least it’s not late winter in the middle of lambing.
on 21/06/2013 1:36am
Could you please advise of what conditions we could expect in Upper Hutt Friday night.
Snow? Rain? Temps?
on 21/06/2013 3:54am
Hi there – same as the Wellington forecast but probably a degree or two colder with a higher chance for sleet tonight or tomorrow morning. Chance of snow – MAYBE – down to about 100m for a brief time, but can’t imagine it will be much (or even noticed by many). Cold southerly still.
on 20/06/2013 7:26am
Is there a chance of snow in Ongaonga tomorrow, our altitude is around 200m.
on 20/06/2013 8:04am
Chances are not looking very good. Slim chance in the morning then again overnight tonight but more likely higher up.
on 20/06/2013 6:30am
Hi, do you think there’s any chance of snow (even just a tiny bit) in Auckland? Thanks 🙂
on 20/06/2013 7:59am
Chances are not good at all for snow in Auckland sorry to say.
on 20/06/2013 4:55am
Hi there, can you tell me please what we should expect in Picton.
on 20/06/2013 7:46am
Snow would seem unlikely in Picton. The surrounding hills could get some though 🙂
on 20/06/2013 3:25am
It seems that there has been an unusual increase in the amount of Twisters in NZ.
Is this purely because of better technology/ phones etc to catch these, or do you think that we are getting more than say 10 yrs ago, and more than likely to see more over time.