Stratosphere watch 2023-24

That's just the GFS, just a different way of looking at 10hPa. Can see it's trying to split the two vortices.

There is still to be interest to be had in terms of the stratosphere when all is said and done. We are not getting a major SSW at least for now during the second week of January which would have been great to re-enforce the idea of blocking down the line when the MJO cycles back towards the Maritime Continent.

There's still evidence of a split on the charts, such as below from the ECMWF. This chart is also for 30hPa which is more relevant for our weather than 10hPa (where the technical major SSW has to be reached). One small lobe going over towards North America whilst the other piece of the energy which is much bigger towards Siberia. I do not particularly like how close that NA lobe is to Greenland which could be important for building heights properly northward but definitely a split here.

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Had taken a break from here for a few days because with life being troublesome, my posts would have come across as antagonistic with lots of toy throwing. I'm still not feeling the greatest but enough to update on the stratosphere and I think it's about time that I did.

There continues to be the signal of another attempt of a minor stratospheric warming through the third week of January. The most recent available 12z EPS had 46/51 of the ensemble members showing a reversal or getting to major SSW criteria at 10hPa 60N. The EC46 mean is also fairly close to 0 m/s. The GEFS drop out about 8 m/s on the 16th/17th and not a single perturbation gets to reversal. Given what has happened recently and the lack of a Ural block, I am more willing to believe in the GEFS here rather than the EPS and be surprised if the EPS do not backtrack.

Does the fact it is a minor or major SSW matter? Not in this case no. I have already answered this but seems it needs to be reminded. If we are to get a major event, we're not talking February 2018 or January 2009 levels of reversal getting down to below -20 m/s. We're talking within -5 m/s and 10 m/s. There won't be a significant difference in impacts from this sort of range. The stratospheric polar vortex is in a very weak state to where it should be for the time of year regardless of which exact speed you get. Also, the major SSW criteria is a bit arbitrary. It refers to ONLY getting easterlies at 10hPa in the stratosphere and 60N over the North Pole. The lower stratosphere is of more importance to us.

As far out as the GFS operational run goes (+384 hrs), the U-60N doesn't get any higher than 13 m/s at 30hPa which is weak. The SPV is very much displaced over Europe throughout its run. There is splitting going on through the current week and the third week as you can see with the daughter vortex placed over Europe and a smaller vortex lobe over towards North America. That hasn't changed at all despite the chaotic modelling for our actual weather with regarding this retrograding of high pressure through the third week of the month. This is set to continue for at least another week or so before the two combine with one another again though remain displaced from its normal position over the North Pole and further minor warmings occur around the Pacific side.

50hPa even lower down is identical with a SPV split visible and a very weak U-60N of 8 m/s.

Additionally, Amy Butler has put out a great blog post regarding the recent "failed" major SSW and an in-depth explanation to understand why it did - a lot to learn from this. She also confirms the split in the lower stratosphere that I mention:

We can see this split imprinted on the troposphere. I have marked the two vortices to make it as clear as day to see. See how the Scandi vortex is bigger than the NA one, as per the stratosphere. In between the two, we see a retrograding high pressure to Greenland with high pressure right over the pole. The trouble has been how big will this high pressure system build and force any low pressure systems to undercut. The strength of the high is not driven by the stratosphere, warm air advection is what inflates it coming from the mid-Atlantic via that vortex over North America. It is looking like there will not be sufficient WAA to develop into a proper anticyclone, rather weak ridging which may still be enough to force low pressure systems southward at least for a time but its weak nature and northerly latitude means Ireland is vulnerable to these systems so could be proper snow makers for some whilst others will be graced with cold rain. The strength of this ridge or blocking high pressure will determine how long cold stays around as MJO passes through the Maritime Continent (zonal).

If you're looking for intense sea effect type showers and a long fetched easterly wind, I think you'll be disappointed and it's time to look for something else in the meantime to chase or wait patiently for the next attempt in February.

The GFS 12z operational saw a full 24 hours of just barely reaching reversal from Tuesday into Wednesday. Tuesday's mean daily value would probably be negative resulting in the weakest major SSW I would have ever seen. Doesn't deserve to be called a MAJOR.

ECM has been similar from what I've heard though runs a day behind publicly. Of course I'm referring to the OP, not the EC46.

Yeah reversal or "easterlies" is when the U-60N go negative, even something as close as -0.1 m/s is a technical reversal and for a major SSW to be officially designated, a mean daily value below 0 m/s needs to be achieved at 60N 10hPa. If it doesn't then it's classified as a minor SSW regardless of how much warming actually happens. Thing is, we've never had a situation like this as far as I'm aware. Normally these events occur via huge heat fluxes and lots of wave activity via Ural block/Aleutian low coming off the back of strong PV events which haven't happened.

The closest I can think of is the failed major SSW of January 2017. The U-60N dropped to a mean daily value of 0.1 m/s on January 27th 2017. I remember talking this event up for a few weeks at the time following the Christmas to New Year flop. What made matters worse in disappointment was the continent had genuine cold - the blocking high over Ireland, as January 2017 was very dry here, favoured them. So got excited at the prospect for something to maybe finally force the high into a position favourable for us. The ECM ensembles showed the reversal at a moderate chance getting down to -10 m/s at one point, solidly major SSW territory. Didn't even reach reversal in the end.

NAM dripping paint cross section shows this minor SSW probably led to the February 2017 easterly and Scandinavian high. However, there was a lack of cold air to tap into and things never set up quite right for us to get a snowy easterly - pffff as if that never happens here.

2023-24 finds itself in a strange position to where we've had a weaker than average stratospheric polar vortex for most of the season so far aside from the brief spike up to average in late December which would be followed by the recent minor SSW that peaked on January 5th and likely aided in the tropospheric polar vortex splitting this week but only temporary. We don't get much of a renewed warming for this secondary attempt making it seem even more weird if we do get a technical major event designated.

I didn't get to see that control run before it was replaced by future runs but I see two possibilities:

1. It sees record-breaking wave-2 activity occur during late January/early February that would lead onto a very major warming through mid-February at a similar time to 2018.
2. Something went wrong in the modelling or coding on the TWO site to show it going mental. Weatheriscool which is the site I mostly use for the GEFS didn't show any huge outliers like that on its 0z update.