summer blizzard

Interesting tropical profile during October. You can see that we have cycling through Pacific waves with a dead Indian Ocean (loosely, MJO phases 4-5-6-7-8-1) however this has been superimposed with a retrograde standing wave.

25OCT2023: Nino3: 2.0 , Nino3.4: 1.6 , Nino4: 1.3 October ONI should come in at +1.6. ASO ONI likely to come in around +1.5.

Is that for Dec-Feb.

No, near solar maxima. https://spaceweather.com/

7.6C, 98mm

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.

18OCT2023: Nino3: 2.1 , Nino3.4: 1.6 , Nino4: 1.3

GFS and GEM/Euro split towards day 10. GFS tries to cut a trough south which pulls the low complex east. The others strengthen this low to our north west. Strong northern blocking though.

I would still urge caution, I think that far too many of you are far too optimistic. That said, I do expect Q1 to average colder than average.

09 did not really have the same setup. November was dominated by a Sceuro block and south westerlies which was replaced by an Atlantic High before retrogression brought the great cold spell. While less stormy, this is more like 2000 or 2019 which basically saw a cyclonic stream on a fairly southerly track. Yes. The first half of December was cool and anticyclonic. The second half of Dec to Mid January was sub zero CET and snowy. The second half of Feb was also snowy.

Interesting. That suggests that there is strong support in the long range Euro ensembles and Glosea.

11OCT2023: Nino3: 2.1 , Nino3.4: 1.5 , Nino4: 1.3

If we are talking about humans in nature then i'd agree with the assertion that we are a tropical species. When you take away proper clothing and shelter, only the tropicals remain viable year round (the moisture prevents absurd maxima and cold nights). If we are talking about humans as we are (i.e. clothed and sheltered) then i would say that the southern temperate zone is most hospitable. We don't cope well naturally with sub 10C minima or plus 40C maxima especially well (without modern technology to support large populations). I would therefore suggest that southern France and northern Italy are probably much more ideal in that regard.

Can't post the chart currently (phone won't copy and paste) but the GFS is suggesting a strong wave progressing through the Pacific in around 2 weeks so i'd look for the first week of November to see another pressure build over Scandinavia unless there's more change.

12.4C is required to avoid the top 11.

Basically it illustrates the position (and forecast) of anomolous westerlies (convection) and easterlies (subsidence) in the Pacific, close to the equator. When you have two areas that are competing, this makes things harder to forecast because it's abnormal.

Cold enough for ground frost on cars in BD19.

We appear to have concensus now that our E/SE spell will be followed with an Atlantic pattern to day 10. Personally i wonder if we are not seeing competing signals for week 4. You can see in the chart below that we have standing waves trying to form in both the west and east Pacific.

Euro this morning does not quite transfer the Greenland energy into Russia and so the block sinks, we are then waiting in limbo for an Atlantic trough. GEM is a success and retrogresses to Greenland and does its best floppy easterly to floppy northerly impression. GFS0z was basically a wet version of the GEM. We get the heights over Greenland but the transfer is weaker meaning that we end up with a flabby low slowly moving east. GFS6z is much the same with a stronger Atlantic. I would tend to discount the GFS6z since the other runs keep the Atlantic weak but it does look like the Scandi High will move away quite quickly. Uncertain as yet whether or not this produces a Greenland block strong enough to keep the UK especially cool.

September PDO came in at at -2.94, the lowest September value since 2012. September AO came in at +0.3, the highest September value since 2020. September QBO came in at -0.6, the lowest September value since 2021. September MEI came in at +0.6, the highest September value since 2015.

UKMO has the second low at day 7 at 970mb so its likely to fail. GEM succeeded in pushing through by day 9 with the second low as the Scandi Ridge moves towards Greenland. GFS0z was a horrid halfway house, it pushed the second low through but the low was already at our lattitude so we don't get the fresh continental air (recipe for 10C and cloud all day and night). GFS6z was a fail, the Atlantic wins by day 10 (ignoring FI afterwards). Euro is a fail overall although only just.

JAS ONI came in at +1.3. To update our list and ranking. Our updated list for AMJ. 1957: +1.3 1972: +1.4 1976: +0.4 1986: +0.4 2002: +0.9 2009: +0.6 2014: 0.1 2018: 0.2 2023: +1.3 We remain joint second. To update on our ENSO trades index, September weakened a little to -0.3 but remained net westerly. https://www.cpc.ncep.noaa.gov/data/indices/cpac850 To compare to our primary analogue list since 1979 (standardised): 1986: -0.4 2002: -1.0 2009: +0.4 2014: -0.1 2018: -0.7 2023: -0.3 Remember that our analysis last month showed a corellation between how early the event coupled and eventual strength so this may be another sign that the models are OTT (i still lean in the +1.3 to +1.7 range).

04OCT2023: Nino3: 1.9 , Nino3.4: 1.5 , Nino4: 1.2

Actually quite lovely in the sun.

While it is theoretically possible to sustain a perverse outcome of mild southerlies, I don't see the model support for that to sustain as things stand. While subject to change, the two key things by day 9 on the GFS, GEM and Euro are.. 1) They all shift the vortex away from the Atlantic as they ride our block north, eventually they'd dump into Russia. This basically reduces pressure on our block. 2) By day 9, they all have a second low by the Azores putting energy into the southern stream. So long as you don't have weird GFS style fizzle out then it's likely to either undercut or encourage the high to retrogress. Either outcome is good in our bid for surface cold and frosts. So long as the modelling does not change drastically then yes, it would suggest that the Euro weeklies were right for week 2.