The Weather Outlook

Remove ads from site

Quantum
  • Quantum
  • Advanced Member Topic Starter
28 November 2025 14:52:35
So by the definition of a zonal wind reversal at 60N, which is often used as a benchmark for a SSW (and stratospheric polar vortex collapse) we have seen it happen this year for the first time in recorded history. Never has a technical SSW been recorded in November before. Now I'm not sure this event actually had that much of a temperature rise ironically, since the temperature rise is caused by a deceleration of the zonal winds, and November being November, the zonal winds started off at a weak baseline. Nevertheless this is still a historic meteorological event that deserves a thread and a chance to mark the occasion. 

http://www.weatheriscool.com/media/u10serie_link_img.png 

25/26 (850hpa temp) 11 days snow/sleet falling

18/11 (-4) 19/11 (-6) 20/11 (-6) 01/01 (-7) 04/01 (-10) 10/01 (-7) 11/01 (-3) 30/01 (-1) 13/02 (-6) 15/02 (-4) 18/02 (-6)

24/25 10d

18/11 (-6) 19/11 (-6) 23/11 (-2) 22/12 (-5) 04/01 (-5) 05/01 (0)14/02 (0) 15/02 (0)12/03 (-6) 13/03 (-6)

23/24 8d

29/11 (-6) 30/11 (-6) 02/12 (-5) 03/12 (-5) 04/12 (-3) 16/01 (-3) 18/01 (-8)08/02 (-5)

22/23 7d

18/12 (-1)06/03 (-6) 08/03 (-8) 09/03 (-6) 10/03 (-8) 11/03 (-5) 14/03 (-6)

21/22 12d

+2
Saint Snow
28 November 2025 17:28:42
We await its impacts with all due excitement

(ie, not very much)

Martin

Home: St Helens (26m asl) Work: Manchester (75m asl)

A TWO addict since 14/12/01

"How can wealth persuade poverty to use its political freedom to keep wealth in power? Here lies the whole art of Conservative politics."

Aneurin Bevan

David M Porter
28 November 2025 17:50:41

So by the definition of a zonal wind reversal at 60N, which is often used as a benchmark for a SSW (and stratospheric polar vortex collapse) we have seen it happen this year for the first time in recorded history. Never has a technical SSW been recorded in November before. Now I'm not sure this event actually had that much of a temperature rise ironically, since the temperature rise is caused by a deceleration of the zonal winds, and November being November, the zonal winds started off at a weak baseline. Nevertheless this is still a historic meteorological event that deserves a thread and a chance to mark the occasion. 

http://www.weatheriscool.com/media/u10serie_link_img.png 

Originally Posted by: Quantum 

Going by my recollection, when SSWs have happened in winter, they have more often than not tended to take place in late winter as opposed to early winter or before the meteorogical winter has started, as in this case. 

Was there a SSW event in either December 2009 or December 2010 before those two memorable month-long freezes began?

Lenzie, Glasgow

"A body of men holding themselves accountable to nobody ought not to be trusted by anybody." – Thomas Paine

Bolty
28 November 2025 18:03:48

Going by my recollection, when SSWs have happened in winter, they have more often than not tended to take place in late winter as opposed to early winter or before the meteorogical winter has started, as in this case. 

Was there a SSW event in either December 2009 or December 2010 before those two memorable month-long freezes began?

Originally Posted by: David M Porter 

I don't think so. I think those just happened because there were other conditions in place that allowed cold weather to become established here. The January-March 2013 cold very likely happened as a result of an SSW.

To be fair though, if you're already in a cold pattern, it's actually not favourable to want an SSW as it can knock you out of it. My understanding of how they affect the atmosphere is a bit like doing a total reset on a computer, or throwing a depth charge into a body of water. It mixes everything up and allows it to "start again". If you're in a mild pattern, then there's a chance that the "reset" will create more favourable conditions for cold, but if you're already in a cold pattern, it may well do the opposite.

If I'm not mistaken, I think January/February 2009 was an example of an SSW that ruined it for us. We were in chilly/snowy conditions for much of the winter, before an SSW happened at the end of January/start of February, and it resulted in late Febuary, March and April being exceptionally mild (though that is more favourable from a personal preference at that staage in winter anyway 😄)

Scott

Blackrod, Lancashire (4 miles south of Chorley) at 156m asl.

My weather station 

Retron
28 November 2025 18:17:28

I don't think so. I think those just happened because there were other conditions in place that allowed cold weather to become established here. The January-March 2013 cold very likely happened as a result of an SSW.

To be fair though, if you're already in a cold pattern, it's actually not favourable to want an SSW as it can knock you out of it. My understanding of how they affect the atmosphere is a bit like doing a total reset on a computer, or throwing a depth charge into a body of water. It mixes everything up and allows it to "start again". If you're in a mild pattern, then there's a chance that the "reset" will create more favourable conditions for cold, but if you're already in a cold pattern, it may well do the opposite.

If I'm not mistaken, I think January/February 2009 was an example of an SSW that ruined it for us. We were in chilly/snowy conditions for much of the winter, before an SSW happened at the end of January/start of February, and it resulted in late Febuary, March and April being exceptionally mild (though that is more favourable from a personal preference at that staage in winter anyway 😄)

Originally Posted by: Bolty 

Here's a list of SSWs:

https://www.researchgate.net/figure/List-of-the-Major-SSW-Events-Recorded-Between-1958-and-2013-Peak-lunar-tidal-Peak-ZMZW_tbl1_324608809 

It seems that a blocked spell can help cause an SSW - note, for example, how there was one not long after we'd had our record-breaking cold spell of January 1987 (which saw -20C at 850 reached down here and the heaviest snow I've ever seen). 

As for this one, it'll be interesting to see whether a) ECM backs it up and b) what the effects are. It's a displacement event, as were the ones in November 1958 and November 1968. (Despite Q's assertion, as I've said a few times in the model output thread where I've been tracking this it's only the first one in the satellite era, not the first one ever recorded in November.)

Leysdown, north Kent
Retron
29 November 2025 05:33:51
The ECM analysis shows that we did achieve an SSW yesterday morning, the third such one recorded in November. The other two were also at the end of the month and neither of them seemed to deliver much in the way of snow afterwards - they were also during an easterly QBO and were also both displacement rather than split events. 

https://charts.ecmwf.int/products/extended-zonal-mean-zonal-wind?area=nh&base_time=202511280000 

The 45-day ECM weekly charts show a gradual cooling trend through December, with Christmas week being average (ref 91-20 means) over most of the UK, so worth keeping an eye on.

https://charts.ecmwf.int/products/extended-anomaly-2t?base_time=202511280000&projection=opencharts_europe&valid_time=202512290000 

Leysdown, north Kent
+3

Remove ads from site