Thursday, November 30, 2023

Extra sunlight a silver lining despite cold days

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It may not feel like it, but the solar winter is over and there’s more daylight around.
The upcoming rainfall map shows all regions getting some rain, with the heaviest falls in the western North Island – better than the eastern North Island, says Phil Duncan.
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By Philip Duncan, WeatherWatch

The solar winter is now over – that’s the three months of the year with least available sunlight and the shortest day of the year smack bang in the middle of it. 

Technically the solar winter ended on August 3, but it’s around mid-August that most people notice the extra daylight with around an hour more light in the north of the country and heading towards 1.5 hours more light for the very south of New Zealand. 

Of course there is a thermal lag – so just because there’s more light it doesn’t mean an instant lift in temperatures. Usually July and August are the coldest months of the year but the added warmth in August and September (and sometimes October) can actually make snow storms more likely. All it takes is a big injection of southerly air into a pool of moisture over NZ and you can have a heavy snow storm. Sometimes the North Island can be in the perfect zone for heavy snow in spring due to that set-up.

The weather pattern this time a year ago was very spring-like. This year it’s messier, with some people telling us it feels like spring and others saying it feels very much like winter. Temperatures over recent weeks have taken a tumble, with NZ experiencing a number of days and nights with below normal temps – quite the reverse from previous months, which were a staggering two or three degrees above normal (back in April, May and June for example). 

For many the recent cold (and the wet) has put an end to much pasture growth, so now that the days are getting longer I’d expect to see some change in that and an uptick in pasture growth. Despite the recent cold snaps, soil moisture temperatures are above normal in most regions, including the deep south. This is mostly due to a distinct lack of frosts this winter – although in recent weeks they have certainly ticked up.

West Coast regions are possibly benefiting more than they normally might in a pre-El Niño set-up. Normally rain would be quite frequent for western NZ but the rainmakers – like the one we’re seeing this week – are fractured and broken up. Bringing rain and showers to a number of regions but not necesarily hammering one place relentlessly.

Nelson and Marlborough are also showing some hints of a drier pattern showing up. But Southland and Otago and coastal Canterbury are very wet – and while eastern parts of the North Island are better than they were a few weeks ago, they are still very wet too. 

Waikato is another very wet region – but is also showing some signs of draining a little better than a couple of months ago. Still, it’s very muddy there and with more low pressure and showers this week we’re not out of the muddy woods just yet.

Highlights this week

• Large low pressure zone for NZ this week

• The low is expected to engulf most of the country

• Rain and showers will be broken up this week

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