Winter 2023/24 - Discussions & Forecasts

[SqueakheartLW]

13 hours ago, Uncertainty said:

There are 3 solid weeks of Ural blocking preceding that rather remarkable ec 46 stratospheric temp anomaly. If the former manifests the latter could too. Easy to see then how the long time seasonal model prediction of blocking this winter could actually occur. We look east / ne with baited breath…

What a chart btw! Anomaly shows how unusual it is to have a warming forecast in early dec…

We may even have time for a decent warming early December that slows the vortex right down but a reversal might not be a likely outcome this early but then could pave the way for a major warming in January or February that destroys the vortex.

Maybe there is still some hope for this winter after all and the payback for both El Nino and EQBO in combination could deliver once again like it has done so many times in the past. My analysis in the ENSO thread a few weeks back did show El Nino and EQBO had the coldest winter signal of all ENSO and QBO combinations.

[MattStoke]

5 minutes ago, SqueakheartLW said:

We may even have time for a decent warming early December that slows the vortex right down but a reversal might not be a likely outcome this early but then could pave the way for a major warming in January or February that destroys the vortex.

Maybe there is still some hope for this winter after all and the payback for both El Nino and EQBO in combination could deliver once again like it has done so many times in the past. My analysis in the ENSO thread a few weeks back did show El Nino and EQBO had the coldest winter signal of all ENSO and QBO combinations.

There's also the risk that the SPV recovers after an early warming, reducing the likelihood of sustained cold during the rest of the winter.

[Mike Poole]

3 minutes ago, MattStoke said:

There's also the risk that the SPV recovers after an early warming, reducing the likelihood of sustained cold during the rest of the winter.

There’s also the flip side to that, which is a double SSW winter.  If you discount 2009/10 (there was a SSW in both Feb and Mar), then you have to go back to 2001/02 when 2 SSWs happened during winter, in Dec and Feb.  

[bluearmy]

My opinion fwiw is that we don’t need a reversal in December if we have a weak spv which doesn’t encourage the tpv to ramp up as we usually see in December? 
 

however, the question then becomes if the likely trop patterns in December are going to be conducive to cold in nw europe without strat influence where an actual reversal could bring a strong sustained -AO with coupling.  (Remember that current ongoing neg AO is still with autumn wavelengths with the jet somewhat further north than we might expect six weeks further on) 

[MP-R]

20 hours ago, MattStoke said:

I feel like I've gone into a parallel world.

Jet stream is weaker and more amplified (meridional) in summer due to less of a thermal gradient than in winter when the opposite is true. Blocking high pressure and wave breaking the occurs more frequently in summer and when the jet stream is weaker. Conversely, a greater thermal gradient that occurs in winter leads to a stronger and more zonal jet stream with fewer incidents of blocking high pressure.

This has always been the case in every related weather report, study, professional meteorological video forecast, the Fundamentals of Meteorology uni course I studied, etc etc etc. 

A stronger jet stream will deepen troughs but not allow (or at least make it more difficult for) blocking areas of high pressure to develop and be maintained. 

I would say both are the case here. From experience, with a strong jet one gets high cyclonic impact but it also seems that big highs move in a lot quicker too, albeit normally from the south (although sometimes the west too). Of course, they then mostly get shifted along pretty quickly too. Running the charts through Jan 2020 is a good example.

Compare that to summer when there’s not a lot to shift patterns along so troughy setups hang about but if high pressure moves in, then that can become prolonged too.

Obviously, there are exceptions on both sides.

Id like to see another Atlantic to blocked flip like Dec 2009. More of a summer evolution but the Azores high threw a ridge up that transferred to Scandinavia and the rest was history.

[Met4Cast]

1 hour ago, bluearmy said:

My opinion fwiw is that we don’t need a reversal in December if we have a weak spv which doesn’t encourage the tpv to ramp up as we usually see in December? 

 I think that solution is already out of the question given we’re looking at a potentially record breaking strong SPV during early November following a significant ramping up. 

[Premiere Neige]

15 minutes ago, Met4Cast said:

 I think that solution is already out of the question given we’re looking at a potentially record breaking strong SPV during early November following a significant ramping up. 

If I remember correctly the models (a couple of days ago) also show the strength of zonal winds falling off a cliff late November/early December. 

[bluearmy]

22 minutes ago, Met4Cast said:

 I think that solution is already out of the question given we’re looking at a potentially record breaking strong SPV during early November following a significant ramping up. 

beyond the peak around 10th November there aren’t that many members that sustain a strong spv. However, if the sustained ural blocking fails to verify then that will change 

[Chesil View]

1 hour ago, Met4Cast said:

 I think that solution is already out of the question given we’re looking at a potentially record breaking strong SPV during early November following a significant ramping up. 

A strong pv in early November doesn't leave any solution off the table.

[SqueakheartLW]

1 hour ago, Met4Cast said:

 I think that solution is already out of the question given we’re looking at a potentially record breaking strong SPV during early November following a significant ramping up. 

I'd rather have a strong PV in the autumn as most years see it weaken in the winter if this happens.

When we've had a weak PV in the autumn it seems to have a habit of suddenly going to PV of doom status once winter arrives.

[Met4Cast]

50 minutes ago, bluearmy said:

beyond the peak around 10th November there aren’t that many members that sustain a strong spv. However, if the sustained ural blocking fails to verify then that will change 

Not too many going for a “weak” vortex in December though, certainly not enough to gleam much of a signal given the spread. 

Wave 1 activity is expected to ramp up in November though. November is a key month for SPV development for me. 

[bluearmy]

3 hours ago, Met4Cast said:

Not too many going for a “weak” vortex in December though, certainly not enough to gleam much of a signal given the spread. 

Wave 1 activity is expected to ramp up in November though. November is a key month for SPV development for me. 

Anything below 25 m/s at 10 hpa is ok re spv not ratcheting up the tpv 

however, if you want the strat to impact on the trop then you will probably need something notably weaker - again the point I’d make is that just having a weak spv may not make much of a difference to our cold prospects if the trop patterns in place aren’t conducive to cold 

[damianslaw]

3 hours ago, SqueakheartLW said:

I'd rather have a strong PV in the autumn as most years see it weaken in the winter if this happens.

When we've had a weak PV in the autumn it seems to have a habit of suddenly going to PV of doom status once winter arrives.

Yes a feature of recent Autumns which by and large have been very benign with weak PV, followed by a sudden surge come December.

We are experiencing a notably more disturbed autumn this year, the faster it winds up, the quicker it implodes..  

[Catacol]

8 hours ago, SqueakheartLW said:

We may even have time for a decent warming early December that slows the vortex right down but a reversal might not be a likely outcome this early but then could pave the way for a major warming in January or February that destroys the vortex.

Maybe there is still some hope for this winter after all and the payback for both El Nino and EQBO in combination could deliver once again like it has done so many times in the past. My analysis in the ENSO thread a few weeks back did show El Nino and EQBO had the coldest winter signal of all ENSO and QBO combinations.

Still some hope after all? I’d say the broad drivers are as good as they have been for many a year. If the +IOD can fade as it appears it will, and the atmosphere can couple to Nino which looks distinctly possible, we have a setup ripe for blocking and the statistically strongest context for a SSW. Time for genuine optimism. 

[Catacol]

5 hours ago, Met4Cast said:

 I think that solution is already out of the question given we’re looking at a potentially record breaking strong SPV during early November following a significant ramping up. 

Hmmm. Early season the strat and trop are often disconnected and we have seen often that a trop led warming can ruin a vortex very quickly. Only last year, a wQBO and Nina year, we had a trop block that made a complete mess of the vortex and its attempt to dominate the pattern in early winter. Now we have Nino and eQBO. Much more conducive to blocking. A record SPV in November does not mean it stays that way in December.

[Summer8906]

9 hours ago, Mike Poole said:

There’s also the flip side to that, which is a double SSW winter.  If you discount 2009/10 (there was a SSW in both Feb and Mar), then you have to go back to 2001/02 when 2 SSWs happened during winter, in Dec and Feb.  

Was there an SSW in Feb 2002? Don't recall any effects from that one.

[Dark Horse]

12 minutes ago, Summer8906 said:

Was there an SSW in Feb 2002? Don't recall any effects from that one.

2001/2002 was a poor winter overall. Bit of snow cover end of December here, the rest of the winter was snowless from memory and was unsettled. I remember walking to college and getting soaked quite often! It was no where near as good as the previous winter before it which had a few more snow events. Just after Xmas was brilliant. 

[Summer8906]

15 minutes ago, Dark Horse said:

2001/2002 was a poor winter overall. Bit of snow cover end of December here, the rest of the winter was snowless from memory and was unsettled. I remember walking to college and getting soaked quite often! It was no where near as good as the previous winter before it which had a few more snow events. Just after Xmas was brilliant. 

Yes, I remember that - hence being surprised that there was an SSW in Feb 2002.

Hoping the hints of a more interesting winter above do come to fruition - after this wet autumn and the wet summer, the last thing most of us need would be a mild, dull, wet winter I suspect!

Edited October 27, 2023 by Summer8906

[Mike Poole]

41 minutes ago, Summer8906 said:

Was there an SSW in Feb 2002? Don't recall any effects from that one.

Yes, according to the NOAA compendium:

NOAA CSL: Chemistry & Climate Processes: SSWC

CSL.NOAA.GOV

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NOAA CSL: Advancing scientific understanding of the chemical and physical processes that affect Earth's atmospheric composition and climate.

Not all SSWs are followed by UK cold, this one in Feb 2002 seemed to be followed by a +NAO, so I expect it went unnoticed.

In other news, the +IOD appears to have now peaked:

Hopefully this will limit its impact to less than 2019/20, and allow the other, positive, drivers like the eQBO to have impact.

[summer blizzard]

Important to note that the CET only correlates with the AO about 70% of the time and the AO is not negative for long after 100% of SSW events. Hence the reasonable expectation being more like two thirds of the time for a favourable impact (though as the likes of Jan 19 show, if the background pattern is hostile then it's not going to do much more than give you a reasonably cool spell). 

In terms of polar vortex formation there are a few ways to think of it and I have never been sold on either fully. Basically there is the view that if the trop and strat are disconnected from the off then you need less of a punch and can kill the vortex fairly quickly - I am not sold on this because most winters see the vortex rebound after early warming events and for scientific reasons, once you get a big vortex hit, it tends to stop the pressure building up again so most winters don't then see sustained pressure. The second idea is essentially that actually so long as it's near average and not raging, a coupled trop and strat are actually beneficial in that if the strat then becomes disturbed the impact is felt through the troposphere. 

It's also worth remembering that polar vortex strength is not the only thing that dictates our weather. Notably, as we entered both December 2016 and 2017 i recall people being very excited because the vortex was very weak, in the end both cases saw the vortex rebound and neither December was anything special. We did get the second hit in Feb 18 but nothing in winter 17. Likewise, you have cases like winter 2012 whereby after a fairly zonal November and December 2011, we saw a failed SSW in January (vortex did drop to single digits) but actually that was enough to produce the coldest first half to February since probably the 90's. 

Point being, people should calm themselves when thinking about the polar vortex and SSW. I'm a big fan of the idea that the overall background can create a 'kind troposphere' as was the case in winter 08/09 when the vortex weakness was nothing special pre-SSW but winter delivered on a scale not seen in over a decade or of course, a hostile troposphere whereby a winter which on the surface has good telleconective patterns ends up underperforming. 

 

[syed2878]

VERRY INTERESTING WATCH THIS THE SECOND SEASONAL MODDEL ROUNDUP FOR WINTER 2023 2024 FROM GAVS WEATHER VIDS A MIX SIGNOEL ME THINKS.  HERE IT IS ANYWAY FOR THOSE OF YOU WHO HAVEN'T SEEN IT YET.  

 

[blizzard81]

I'm liking the latest trends at week's 3 & 4 from the cfs. Blocking becoming stronger and stronger to the north east as we approach the end of November. 

[SqueakheartLW]

Volcanic eruptions found to dampen Indian Ocean El Niño events for up to 8 years

PHYS.ORG

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Volcanic eruptions occurring in tropical regions (23°N/S of the equator) have been linked to abrupt disruption of global-scale climate cycles in the Indian Ocean over the last 1 million years in...

 

Here's a good read for you all. Consider this one in regards to that big volcanic eruption we saw in the tropical Pacific last year.

[MP-R]

20 hours ago, Summer8906 said:

Was there an SSW in Feb 2002? Don't recall any effects from that one.

The SSW that winter may have been what spelled curtains for the second half of the season. Up until that point it was generally a good winter.

[SqueakheartLW]

5 minutes ago, MP-R said:

The SSW that winter may have been what spelled curtains for the second half of the season. Up until that point it was generally a good winter.

It is known that -AO and especially -NAO just before and during the SSW is a bad setup to have. The SSW will very likely flip the pattern to +AO and +NAO if this happens.

The opposite is also true in many cases too.