Sudden Stratospheric Warming Event (SH) 2019

[Achten]

Well done Guys on your assumptions, predictions and explanations it has been a fascinating read.

[Cyclone Tracy]

The earlier warming of the stratosphere is quite graphic when compared to this time last year. The Ozone hole has now completely closed. I've had a close look at past early stratospheric warmings (back to 1979) along with ENSO, IOD and the SAM index in those years and there is no clear precedent when you add all 4 components together. There is also the solar minimum as mentioned earlier in the thread but this also seems different to early 00's.

In my opinion, it is a lottery to forecast NZ's weather for the upcoming December. The EC ensemble is also flip flopping on the monthly outlooks now going for a below average December temperature for NZ as a whole compared to it's October model run.

Ozone 13 Nov 2019 2018.jpg

[Cyclone Tracy]

2 cents worth.

34th consecutive day of a SAM (AAO) index being negative as the SSW flow on effects continue to flush out. Powerful upper troughs doing the trick for the SI this week injecting both 18th & 20th November with abnormally cold uppers above Canterbury. The Rossby wave wheel of fortune now moves on for a week or so.

GEFS ensemble continuing to lock the negative SAM sequence into December. With the South Pacific convergence zone now becoming more active, something big is brewing for December.

GPH 20 Nov.jpg

SAM 2011.jpg

[Cyclone Tracy]

Latest dripping paint chart showing that the SSW side effects are going to go well into summer.

GPH 26 Nov.jpg

[Cyclone Tracy]

40th consecutive day of the negative SAM (AAO) index sequence and the GEFS ensemble is dropping off the cliff again. Some members are dropping to -4 for the start of December. The long wave trough is again targeting Australia with Tasmania and Victoria about to have one of the coldest starts to summer in recorded history. EC is projecting snow over 70% of Tasmania late this weekend including flurries in Hobart with snow down to 800m on the mainland. Bush fires will flare again for NSW & QLD. NZ impacts will be big north westerlies for parts of the South and North Islands from Monday to next Thursday with significant rain on the west coast of the SI.

EC 2611.jpg

[Chris W]

Should be some good severe storm potential for both islands in the mix.

70hPa vortex is all over the show now, a stronger lobe southeast of South Africa but elsewhere slowing, splitting and snaking in various places. Means the 250hPa polar jet is all over the show as well though it is roaring across the 40s and furious around the fifties, leading to that Aussie fire weather and our NWs. The positive Indian Ocean Dipole is also driving that, given NIWA's seasonal outlook.

[spwill]

I am happy NZ is on the warm side of the pattern for a change.

[JP.]

I am happy NZ is on the warm side of the pattern for a change.

Indeed! I am as well. Been a very warm November in Christchurch

[Cyclone Tracy]

Hot and cold records are being broken between OZ and NZ. NZ warmest November on record has been backed up by Australia's coldest summer day on record. Luck of the draw which side of the atmospheric fence you are on . SAM (AAO) index currently down to near -3 with now 47 consecutive days being negative.

Article from Australian meteorologist Ben Domensino originally posted in the Australian weather thread by Tich but is also relevant for this thread for reference to the SSW.
https://www.weatherzone.com.au/news/col ... ord/530627

[Willoughby]

Very warm start to December globally - look at how the SSW has fully engulfed the frozen continent. Cool SE Australia - but that will become warmer than normal by EOM. Very warm WA and NZ either side of that.

image.png

[Richard]

Fascinating. Been noticing the temps in the Siberia area of late, some brutal -40's and lower.

[Cyclone Tracy]

The dripping paint chart is now displaying that the 2019 SSW has surpassed 2002 with regards to the strength of the coupling between the stratosphere to troposphere and continues to penetrate into mid December with the SAM index now 56 days consecutively negative. The Rossby wave train is starting to set it's sights on NZ leading up to Christmas.....

SSW 2019 v 2002.jpg

[Chris W]

I'm fearing for the popcorn supplies, we've given them a thrashing this spring/summer.

[Richard]

Dont worry about, I'll see ya right.

[Chris W]

70hPa winds over NZ are still a mess and pretty weak. The jet to our west is all go but once the systems get here they might temporarily run out of steam?

https://earth.nullschool.net/#current/w ... 80,-41.653

The 250mb jet reflects this, taking a strong southward dive after passing NZ. I don't really know what that means except maybe continued changeable weather as the upper winds remain in a mess.

[Cyclone Tracy]

2 cents worth.

The relentless negative SAM (AAO) sequence has come to an end. 66 days straight, finally tipping into positive on 24 December. Many extreme's were observed across the southern hemisphere during this time but the strong westerly influence on the Australian bushfires along with the west coast South Island rainfall were probably the most significant impacts. It all came down to the timing and position of the meridional jet stream. A lack of moisture due to the positive Indian ocean dipole meant that sub tropical latitudes had a drier and warmer period during the sequence.

AAO 25122019.jpg

[Chris W]

CT, have a look at the GFS today and see how long you think that SAM will be positive for! Not sure January will be all that settled to start with.

[Cyclone Tracy]

CT, have a look at the GFS today and see how long you think that SAM will be positive for! Not sure January will be all that settled to start with.

Yes, it wont stay positive for long. How deep it goes into negative is a little uncertain though. NASA and EC are picking up an unusually strong upper cold shot in 10 days time into the SI.

[spwill]

The GFS/EC model outlooks still have the westerlies and highs tracking a bit further north than you would expect to see them this time of year.

[Chris W]

Consistent with the SSW impacts, the models have finally got it.

[TonyT]

The GFS/EC model outlooks still have the westerlies and highs tracking a bit further north than you would expect to see them this time of year.

Its all going to change by mid January though, watch the anticyclones track over the South Island, and some easterly airflow start to affect the North Island.

[Richard]

The GFS/EC model outlooks still have the westerlies and highs tracking a bit further north than you would expect to see them this time of year.

Its all going to change by mid January though, watch the anticyclones track over the South Island, and some easterly airflow start to affect the North Island.

yes, inland heating,

[Razor]

Looks like the SST is clearly implicated in the conditions leading to the Aussie fire disaster. Fascinating read.

https://i.stuff.co.nz/environment/clima ... -firenados

[Cyclone Tracy]

NIWA commentary from yesterday for the thread.

"The most common question we've gotten in 2020 so far: why has summer been not very summer-like?

1. Near-record positive Indian Ocean Dipole. During late spring and now into summer, this climate feature kept high pressure locked in over Australia, encouraging continued drought, with New Zealand stuck along its peripheral windy and unsettled southwesterlies.

2. Sudden Stratospheric Warming. Remember this one Although its time as a climate driver has ended, it still had an influencing role from late spring into early summer. It led to a strongly negative Southern Annular Mode which meant that the pressure over the pole was higher than normal. When the pressure over the pole is higher, the pressure over the mid-latitudes (e.g. New Zealand) is often lower, bringing less-than-ideal conditions.

These two climate features have worked in tandem to bring more southwesterly winds to NZ from the Southern Ocean.

For the South Island, this has meant cool temperatures and unfavourable weather, particularly in the south and west. In the North Island, it has been a bit drier but fairly cool in lower and western parts. "

[Chris W]

It seems to me like the subtropical ridge has largely 'recovered' from the SSW over NZ in that we're heading into a more regular summer pattern. meanwhile over the South Atlantic the jet is still way further north in the direction in which the vortex was pushed out by the warming. I'd say the impacts are waning now. Maybe the change in the IOD helped?