Why has there been so much thunder?

Tāmaki Makaurau - 114,765 lightning strikes have been recorded over and near Aotearoa in the last week, the Metservice says.

The thunderstorms, for which MetService has issued a raft of warning and watches in place, also brought downpours, hail and strong wind gusts, with tornadoes also reported.

MetService meteorologist Tui McInnes says it is an immense number and New Zealand is not even halfway through the month and June this year has recorded the second highest monthly amount of lightning strikes since records began in 2000.

“There are three main factors: an atmosphere prone to having low pressure, southwesterly polar-outbreaks and warmer-than-normal waters for most of the country,” McInnes says.

“The first factor has Aotearoa under an atmosphere ripe for low-pressure. The last week has seen us under a planetary trough, which means the atmosphere prefers low-pressure systems over the country resulting in an almost-continuous barrage of lows and fronts.

“Helped by the atmosphere, southwesterly polar-outbreaks have generated the stormy weather dominating our skies.

“When we talk about polar-outbreaks, we refer to a weather system where cold air moves north, over warmer water. This is important as it creates instability, which is required for thunderstorms to develop.”

Finally, a marine heatwave has had a significant impact in intensified how active this weather has been, making the skies very electric. With polar outbreaks, colder air moving over warmer ocean is important. Throw in water that’s warmer than usual into the mix and there is so much more energy into the system; it’s like doubling the baking powder when cooking muffins.

The end result? Near-record breaking amounts of lightning, plenty of heavy rain, large hail stones, strong wind gusts and even the odd tornado.

Lightning and thunder aren’t the only impacts; polar outbreak conjures visions of bitterly cold, wet, windy weather. The snowfall in the South Island high country is a testament to this, with significant snow down to 500m in places, closing roads and mountain passes and making for some picturesque landscapes. We are in winter after all!

With all this talk of stormy weather, what is the outlook for the remainder of the week? There are a number of severe watches and warnings in place, however, there certainly is a settling trend. Wet and cloudy weather lingers around in western areas, but elsewhere expect to see the sun a bit more during the working week.