NZ Weather Forum

Lower stratospheric twin sisters appearing again at the start of October on EC. GFS showing a significant deterioration of the vortex structure at the same time. It doesn't show up on the models for NZ yet but there is a decent October cold snap on the cards for NZ if they verify.

Showing up on GFS this morning.


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GFS has been relentless in modeling heat flux attacks on the vortex. Not all have materialised including today's (my post on the it 16th) but it is clear that the vortex is being destabilised fairly quickly this year. The right alignment could lead to a strong cold blow for NZ, or not much if it aligns in another direction.

Showing up on GFS this morning.

not so much now
but now Euro model does have a polar high south of the tasman sea

GFS continues to launch all it can at the vortex (yes I know it’s a model), planting a large area of close to 0C air over the pole and indeed most of the continent at the end of the current run. Could be an early end this year if that does happen.

GFS continuing to nail the vortex hard this month, ramping up with a warming up above 0C at 10hPa from mid-month.

https://www.metcheck.com/SEASONAL/strat ... ecasts.asp

Wild weather from the south looking largely unlikely for NZ from now on. More likely cut-off lows or Tasman/subtropical from now depending on what goes on in those areas.

Warm air flooding the stratosphere above the ice sheets at 10hPa; up to -24C with the cold air very isolated and pushed away to Chile. Vortex there has shrunk massively and disintegrates at that level by the end of the month.

Lower down, GFS has a lobe approaching close to NZ in 10 days' time so a potential cold outbreak then as it is also modelling for the troposphere.

NASA now projecting the Polar vortex to be near the strongest that's ever been recorded at the end of October. This year's strength has contributed to the coldest winter ever recorded at the South Pole (1957 to 2021). Last year the final warming was the 2nd latest ever recorded on 14th December. The Record is 15th December 2010. The 2019 Sudden Stratospheric Warming event helped trigger the final warning on 30th October 2019.

Something's off then (perhaps my interpretation of the 3D vortex) but GFS seems to be angling for its disruption/demise sooner than later.
https://stratobserve.com/ens_ts_diags

Perhaps I was looking more at 1hPa than 10. It seems odd though, as there's a lot of warm air/increasing Ozone concentration over the continent at 10hPa but the vortex seems to carry on anyway.
https://www.cpc.ncep.noaa.gov/products/ ... sh_f00.png

Everything else seems to support CT's observation though. I'm a bit stumped.

Yes, the vortex is definitely weakening and losing form but at a much slower rate again this year. The one interesting thing in common for the late warming years of 2010, 2020 & this year is all are La Nina's in the Pacific.

GFS signalling the end of the 10hPa vortex around December 7th, other ensembles seem to broadly agree (+/- 2 days) as mean zonal winds reach 0kmh and shift easterly:

https://stratobserve.com/ens_ts_diags

A brief resurgence but ensemble members all now end the vortex on Monday 13th. So pretty late in the end.

Confirmed that the vortex at 10hPa is no more and zonal winds shifted easterly yesterday- so December 14th, tying second place for the latest warming going by CT's earlier post:

https://stratobserve.com/ens_ts_diags

https://www.cpc.ncep.noaa.gov/products/ ... mb_60S.png