This Spring could be even more volatile than normal, says 1News weather expert Daniel Corbett.
Spring and Autumn are always known as the seasons of transition, but this Spring could have even more octane in the mix.
That will be down to some big players in the atmosphere jostling for centre stage in our weather.
As a season of transition, it’s the time of year between our fading Winter and the warmer season of Summer. We do often associate Spring as a more boisterous time for weather where we can have four seasons in a day.
But what happens to shift the weather calendar from Winter to Spring and then ultimately Summer?
We all know that as the days grow longer from late June to the third week of December the strongest most direct rays of the sun are heading back down to our part of the world.
That sunlight or warmth is one of the key ingredients for weather. The other big player of course is cold (aka Old Man Winter).
The cold intensifies during the Winter in the 24 hours darkness which occurs at the higher latitudes of the Southern Hemisphere during our Winter. This grows that thing called the Polar Vortex. I call that Old Man Winter’s store cupboard.
So why is Spring going to be a wild ride this year?
Increasing power in the sun
Most Springs have a bit more oomph to them because the increasing warmth from the sun’s rays returning to our hemisphere slam right into Old Man Winter and his polar darkness down on the ice shelf of Antarctica.
The time when the first sunlight and warmth return to the polar regions is a bit like if you have ever seen someone poke a hornet’s nest with a long stick. The hornets get annoyed and start buzzing around in a fury.
That warmth hitting the polar regions acts in a similar way, just a bit less frenzied. The contrast of warm and cold creates a gradient which generates wind and lift. In turn, they are the building blocks for weather.
This Spring, because of the Winter wobbles to the Polar vortex, caused by more intense warming from more northerly regions, combined with a more active Indian Monsoon (generating even more warmth), we could get days when it seems like we are having four seasons back-to-back.
One day it might be t-shirts and shorts with unseasonable warmth from Australia and then just the next it might be back to the merino as a late Winter blast of cold arrives, possibly even with snow in some regions.
Think of it like that fast-boiling pot on the stove and the bubbles keep churning to the surface.
You might wonder what the Indian Monsoon has to do with our weather, but not only will it be a good source of warmth and moisture to help provide the oomph and fuel to weather systems heading our way, it might also play a part in how the NZ Summer weather shapes up.
La Niña v El Niño
There are already good indications that the El Niño weather pattern of last Summer will be replaced by a La Nina pattern.
Before you start to think, “Oh, no flooding up north again this Summer,” remember each La Nina is different and how it develops is based on how the various ingredients mix.
It’s a bit like making a lovely sponge cake from memory, each time it might taste slightly different. In our case with La Niña, it is not only how the seas and air circulations develop across the Pacific Ocean but also what’s happening in the Indian Ocean. In particular, the Indian Monsoon and how that massive circulation fades as it shifts back south to the Equator in the next month or so will play a key part.
La Niña creates more of a eastward push of air across the Pacific Ocean, which is the opposite to El Niño. As a result, the big difference in our weather will be more humid northeasterlies spreading down across the northern half of New Zealand as our typical Summertime highs shift further south than normal.
If the steering winds align correctly this moister flow can lead to higher amounts of rain to northern parts of the country – but not always. Time will tell… Watch this space for more over the coming months.
So Spring might keep us on our toes with a good mix of fine, warm, cold, wet, windy and even the odd brief fading blast of Winter.
Buckle in, here it comes!
