By Rebekah LaBar, MetService Meteorologist

The low-pressure system that brought cold weather, snow, and thunderstorms to New Zealand is pulling off to the east today. An unsettled southwest flow will continue to dominate the weather this week, although temperatures will gradually rise as we head towards the weekend and the recent snowfalls will start to melt.

The following image from a NOAA satellite shows the centre of the low just southwest of the Chatham Islands. Note also that in the clear skies north of about Mount Cook, the white in the central Alps and Kaikoura ranges is snow. Clouds are still obscuring much of the lower South Island, not allowing us to see the coverage of snow beneath.

noaa2135Z False colour image, courtesy of NOAA, at 9:35am local time
False colour image, courtesy of NOAA, at 9:35am local time (zoomed in view) False colour image, courtesy of NOAA, at 9:35am local time (zoomed in view)

You can also see in the first image the next frontal system approaching the southern South Island (the long thicker cloud band). This is only a weak system and will not bring much more weather with it aside from the ongoing showers.

Showers will continue to affect much of the North Island mainly north of Wanganui today. Wintry showers will also continue across Banks Peninsula (snow level above 200m at first but rising through the afternoon today) and the lower South Island, including Southland and southern Fiordland and Otago (snow level above 300m at first but rising to 800m through the afternoon today).

Snow reports

[embed]https://twitter.com/RossGrahamnz/status/587698527477731328[/embed]

So far the largest snowfall total that has been reported in the last 24 hours or so is 30cm at an altitude of 500m at Strathview Station (northeast of Clarks Junction, inland from Dunedin). The observer reported that most of that fell during Monday, but there was another 10cm or so overnight.

There was a report of 8cm of snow that fell at Gore and 3 to 4cm that fell at Clinton (altitude 192m), just to the southeast.

[embed]https://twitter.com/RobynMourie/status/587717132781129728[/embed]

The North Island also saw some snow, with reports coming in mainly from the central plateau and a few centimetres settling on the Desert Road.

Frosty weather still to come

Inland parts of the South Island are expected to see some frosts early Wednesday morning, as mainly clear skies will allow temperatures to become chilly again tonight (aside from the far south that will still be under some cloud cover).

Marine impacts

Heavy southwesterly swells of 5m will continue to build along the east coast of the country and the Chatham Islands today. The seas are expected to increase in height as we head overnight Wednesday into Thursday, spreading from the south.

Combined wave heights (in metres) for midnight Wednesday by the ECMWF model Combined wave heights (in metres) for midnight Wednesday by the ECMWF model

mapmetocean

Forecast wave spectra images from Cook Strait for Tuesday through Sunday, courtesy of MetOcean Forecast wave spectra images from Cook Strait for Tuesday through Sunday, courtesy of MetOcean

What is it that you are looking at? The colourful images above are of the wave spectra for the two points as shown on the map. This wave spectra looks at the energy in the waves. One will often see this after a frontal system has moved through a region, that the bigger seas with the higher energy in the waves have a delayed effect on arriving, in this case following the front that moved through Cook Strait on Monday afternoon. When looking at the wave spectra we can see that the waves with the most energy are expected to be felt on the southern coastal regions of the Wairarapa and Wellington overnight Wednesday into Thursday, associated with relatively long period swell of between 12 -14 seconds. The upper eastern coastal regions of the South Island and southern and eastern coastal regions of the North Island are expected to feel the brunt of these larger, higher energy waves in the next day or two as the winds turn more southerly.