New Zealand has a higher-than-usual risk of sharp cold snaps and unsettled weather, especially for the South Island, during the first half of the season, said the National Institute of Water and Atmospheric Research (NIWA) in its seasonal climate outlook for spring.
A rare sudden stratospheric warming (SSW) event is unfolding 30-50 km above Antarctica which will likely lead to unusual and extreme weather in parts of the Southern Hemisphere.
SSWs are a dramatic warming of the air at the stratospheric level — a minor event is defined as a warming of at least 25C in less than a week, while a major event involves both a substantial warming as well as a split in the polar vortex.
Looking back, there have only been two SSWs on record in the Southern Hemisphere — one in September 2002 (major) and another in September 2010 (minor).
As far as New Zealand was concerned, the 2002 SSW event resulted in a significant cold outbreak in October while the 2010 event was associated with record rainfall during September.
Air pressure is forecast to be lower-than-normal in the Australia/New Zealand region during this September-November, which should mean an increase in Antarctic air from the southwest.
“The warm seas that helped to modify sub-Antarctic air masses earlier in the season have now cooled,” NIWA explained. “The flow-on impacts can take days to weeks [to develop], as the SSW can encourage a weaker polar vortex allowing streamers or pockets of polar air to break off into the mid-latitudes.
“Consequently, there is an elevated risk for periods of unusually active weather during spring 2019, including sharp cold snaps, especially in the first half of the season,” said NIWA.
The cold times are returning, in line with historically low solar activity.
Go confirm the data/historical documentation for yourselves.
Don’t let anyone inform you otherwise.
The time to prepare is now.
Grand Solar Minimum + Pole Shift