© NIWA
NIWA says a ‘Sudden Stratospheric Warming’ event could bring icy weather to New Zealand next month.
It's called a sudden stratospheric warming event - and, unlike the name might suggest, the rare phenomenon could spell a burst of bitterly cold weather for New Zealand over coming weeks.
A sudden stratospheric warming (SSW) event kicks off when the temperature of the stratosphere - that's 30km to 50km above ground - over the South Pole climbs by more than 25C. Meteorologists think it's likely this is about to happen next week.
Importantly, it has the potential to mess with a ring of stormy and freezing weather that encircles Antarctica, which is at its strongest at this time of year - and which we know better as the polar vortex that's been dubbed the "beast from the east" - threatening to send a series of cold blasts from the North Pole to Western Europe and the UK, along with the east coast of the United States.
While this swirling, freezing air mass is usually effective at keeping harsh, wintry conditions locked up close to the pole, an SSW can help weaken or displace it in the stratosphere.
This sends these cold masses filtering down on to the tropospheric polar vortex, potentially influencing our own weather patterns.
Niwa meteorologist Ben Noll said that, during a major SSW, the winds in the stratosphere reversed from westerly to easterly.
"For up to about a month after the SSW, polar air masses, known as streamers, can break off from the weakened vortex and move towards New Zealand," he said.
"It doesn't guarantee unusual or extreme weather, but it can happen."
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