NZ Weather Forum

The Southern hemisphere's 2021 stratospheric polar vortex is about to come to life. Winds have swung from easterly to westerly in the last 72 hours, as the most powerful weather system on the planet commences it's new life in 2021. GFS showing the first signs of a rotating vortex's structure on 6 March.

Currently a balmy -39C over the South Pole at 10hPa, light random winds wafting around in places over the Antarctic Circle. 70hPa has a gentle vortex going on but that one never really goes away.

It will be interesting to see what happens after last year's exceptionally-strong vortex, will there be a bounceback and less energy in it this time or not? I note the discussion in the coldest year thread about a cold winter for NZ, so that would seem to indicate a more disrupted, less strong vortex or one that is maybe located more in our neck of the woods rather than hanging out more towards South America as it has since the SSW 18 months ago. Just pontificating, I don't know but do I enjoy finding out

Yes, interesting year ahead. Every year us mere humans learn more about it's influence on the mid latitudes. Last year's near record late final warming on 14th December override the La Nina influence for NZ and delivered some great thunderstorm outbreaks across the country in December when the polar jet was unleashed.

Chris W wrote: ↑Mon 22/02/2021 15:57 I note the discussion in the coldest year thread about a cold winter for NZ, so that would seem to indicate a more disrupted, less strong vortex or one that is maybe located more in our neck of the woods rather than hanging out more towards South America as it has since the SSW 18 months ago. Just pontificating, I don't know but do I enjoy finding out

I'm thinking that is going to be more ocean driven than atmosphere driven. Interesting (though O/T) that we are 6-8 months into the new solar cycle yet sunspot numbers are still way down. The 13 month smoothed SSN to December was the lowest since 1823. If the PDO continues its shift to the Nina side then we could be looking at (at least) several seasons of wonky PV/Jetstream activity.

Well there you are little vortex, first visible signs of a westerly circulation at 10hPa centered over the Weddell Sea/West Antarctic Peninsula:
https://earth.nullschool.net/#current/w ... 98,-76.218

With the stratosphere now becoming organised and winds swinging westerly @ 10 hPa, the upper troposhere is about to be on the move. EC showing an autumnal twin sister circulation in around 10 days @ 200 hPa ballooning from over Antarctic continent. Long wave troughs and the Polar Jet in order for NZ soon.

10hPa vortex now centred over the East Antarctic Ice Sheet and pushing 90kmh in places, it's cool to see it develop from a light breeze through strong wind all the way to full speed through autumn.

https://earth.nullschool.net/#current/w ... 94,-57.144

Signs of a warming across the South African side of the 10hPa vortex in 3-4 days' time that potentially pushes the early vortex NZ's way. Not sure of the likelihood of downwelling impacts but possibly a harbinger of an early winter blast in a month or so's time?
https://www.metcheck.com/SEASONAL/strat ... ecasts.asp

Chris W wrote: ↑Thu 25/03/2021 14:33 Signs of a warming across the South African side of the 10hPa vortex in 3-4 days' time that potentially pushes the early vortex NZ's way. Not sure of the likelihood of downwelling impacts but possibly a harbinger of an early winter blast in a month or so's time?
https://www.metcheck.com/SEASONAL/strat ... ecasts.asp

Fits with 45 day guidance. Third week of April through first week of May showing as cold dominant, disturbed SW airflow.

Warming occurring over South Africa, causing a contraction in the vortex there and helping it over towards us:
https://earth.nullschool.net/#current/w ... 55,-28.722

GFS is currently then projecting that the vortex pulls away towards the Weddell Sea towards the middle/end of run.

Looks a pretty broad Rossby wave at 100hPa over NZ mid-month, possibly some pretty strong winds/increased storminess around then if it couples to the troposphere. GFS says yes to that idea.

Only 26 days until the start of the astronomical polar night over the South Pole. The Antarctic polar vortex, the earth's most powerful weather system is about to go into 2nd gear

10hPa vortex centre sitting just about right over the pole, quite satisfying after it has spent 20+ months (except for summer holidays) getting pally with Chile.

https://earth.nullschool.net/#current/w ... 61,-89.731

10hPa centre goes under -70C. Interestingly the temperature over the Ross Ice Shelf at the surface is now below -50C, the pole is at -63C and Dome Fuji area just about heading below -70C. The coreless winter has begun.

It's happening. The stratospheric polar vortex is developing over the near centre of the Antarctic continent for the commencement of the polar night. That hasn't happened for several years. IMO, long term ridge blocking positions will be changing in a few weeks when the Hadley cell moves more equatorward......The years of blocking boredom in the troposphere that has sent warm and cold core cyclones east and south is almost over.

Also been enjoying seeing that CT, and what's more looking at Metcheck today/GFS modelling it looks like the vortex is inclined to throw some weight in our direction over the next few weeks. Some concentrated patches of Ozone floating around as well. Could be a quite different winter to the last couple, as a complete guess!

Cyclone Tracy wrote: ↑Mon 03/05/2021 20:30 It's happening. The stratospheric polar vortex is developing over the near centre of the Antarctic continent for the commencement of the polar night. That hasn't happened for several years. IMO, long term ridge blocking positions will be changing in a few weeks when the Hadley cell moves more equatorward......The years of blocking boredom in the troposphere that has sent warm and cold core cyclones east and south is almost over.

Right on cue. The SPV is calling the shots now

Yes it looks like a real driver behind the coming weekend's modelling as it looks coupled with the troposphere. After that it possibly hangs around more in our direction for a few days before tightening and contracting after that. However it is centrally positioned this year so it's much more interesting in terms of potential stormy weather for the winter.

EC projecting fully coupled stratospheric and tropospheric twin sisters over the Antarctic continent in a week with a brutal surface temp anomaly below. A top shelf cold shot is brewing for the 2nd half of June.

-89C at 10hPa, brr

https://earth.nullschool.net/#current/w ... 52,-84.020

Stratospheric vortex a bit elongated to our east probably sending the coldest outbreaks that way, will be interesting to see if that changes though disturbances do tend to follow clockwise (west to east) around the pole so could take time.

When that massively below average super cold air from Antarctica escapes when the polar vortex weakens/distorts New Zealand should be in for some epic polar blasts...

https://www.nzherald.co.nz/nz/weather-c ... IEJHJFOEU/

Weather: Cold front, rain to hit most of NZ, as Antarctica plunges to -81C

seems a leetle bit misleading for this weekend's weather!

From what I've seen so far from the GFS stratospheric modeling, any upcoming distortions in the vortex are directed more to the Pacific, South America and even Australia than they are towards us. Particularly South America. Not saying we won't get some, but a lot of it may miss us.

Cyclone Tracy wrote: ↑Tue 08/06/2021 15:45 EC projecting fully coupled stratospheric and tropospheric twin sisters over the Antarctic continent in a week with a brutal surface temp anomaly below. A top shelf cold shot is brewing for the 2nd half of June.

Mt Cook's summit will be near the stratosphere next Monday.

Mentioned in the July thread, but it’s looking like the SPV throws a lobe our way a week or more into July. CT and others, your thoughts?