A cold southerly arrives in the South Island today and covers all of New Zealand by the end of Wednesday, producing a nationwide temperature drop that no one avoids.

Parts of the South Island will today be in the mid-teens, while tomorrow most will have daytime highs in the single digits – just the West Coast and Nelson scrape through to double digits, with highs of 11.

The cold air moves over the North Island during Wednesday and the ‘winterless North” doesn’t miss out either. The Bay of Islands has a high of around 17 or 18 degrees today, which is above average. On Wednesday the high drops by five, down to just 12 degrees.

Queenstown has snow showers in the forecast this week but the biggest of the main southern centres, like Dunedin and Christchurch, are not expecting to see snow to any serious levels – Dunedin may get a few flurries in the higher up suburbs, or sleet. The snow level in Dunedin looks to be around 400m, possibly 300m (for snow to settle). Below that the ground is too warm this year for snow to really linger too long – a positive for farmers. Christchurch isn’t expecting any snow, some sleet is possible.

As you can see from the maps below today is much warmer than average but by Wednesday the cold change arrives and a number of regions go below average. However it’s worth noting that it’s been so much warmer than average lately that even with this nationwide cold southerly temperatures over both Wednesday and Thursday won’t be below average for everyone, with a number of regions finally experiencing “normal” temperatures for late July, while some (like the West Coast) actually tick above average thanks to the sheltering nature of the Southern Alps.

You can also see how short lived the cold snap is, with the South Island returning to normal temperatures as early as Thursday.

– WeatherWatch.co.nz