Stratosphere watch 2023-24

A big PV stretch is evident in the lower stratosphere but placement of lobes isn't great with some of the energy ending up over Greenland.

Very poor GEFS with a minor SSWE followed by a swift recovery by a significant minority - most keeping it around 20 m/s as far out as the forecast period goes.

We've lost the Ural blocking high which is a big loss as far as stratospheric disruption is concerned.

We can regard the major SSW as a major flop I think albeit there was one single run with the EC46 mean getting to reversal..

A minor SSW isn't the end of the world but it's the swift recovery indicated by the GEFS, even accounting for their strong vortex bias, and the loss of the Ural high that concerns me.

There is some slight hints for another down spike in U-60N in the third week of January after this minor SSW is through. No evidence to suggest this would become a major event either but it continues the trend of a weaker than average vortex for the time of year.

One third of the EPS suite showing a reversal (major SSW) for the second attempt of SSW. It really is deja vu isn't it.

There's the minor warming spike now. Much more muted at 30hPa for now, should see a rise through the next week.

Wrong thread WolfeEire, this is the stratosphere thread.

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.

We have already seen the impact if Simon Lee's explanation two posts above is to be believed and any "warm outcome" is unlikely to be directly related to this very very weak major sudden stratospheric warming (likely the weakest of all-time).

We can see the radiative strengthening of the stratospheric polar vortex aloft using the NAM forecast below (the blue colours top left indicating +NAM or similar to positive Arctic Oscillation conditions). This is a normal procedure following major sudden stratospheric warming events, particularly in early and mid-winter when there's still plenty of time for radiative cooling.

Very positive AO surface conditions expected for at least a week before a more muted signal appears with rather neutral conditions though still leaning on the slightly positive side. An indication of low pressure not moving anywhere fast away from the North Pole and blocking is more difficult to develop with such conditions.

All those seasonal models showing a very blocked February in the high latitudes not looking good right now.

Just looked back through the C3S MSLP anomalies for the summer months over various monthly updates (March-June) and I don't see any particular strong signal on the mean from any of them for the summer. Neither indicating a great or terrible summer. Of course you will see better signals in individual models but I tend to use the mean when viewing these models.

Meanwhile, the February blocking signal goes back many many months and has been evident in every single update of the C3S suite means. This would be a massive bust.

Fail to see how this will come off unless we see a 180 swing in the model output with that vortex parked over Greenland which can well happen but...