summer blizzard

7.4 5.5 2.4 - 2021 7.5 5.7 4.8 - 2018 5.2 5.1 6.2 6.2 4.7 - 2013 6.2 5.2 -0.2 - 2010 Took a look at the first halves to Jan given the cool outlook be that UK High or Scandi High. Not many cool first halves means it's not difficult to rank well although we are unlikely to surpass 2021.

Euro tonight has moved to mid-latitude ridging from day 6 onwards. Not entirely surprised and the vortex while weak, will take a while to push down the main thump from the attempted SSW even if it’s failed (tropospheric vortex is much less hostile to weakening than last year so I don’t think it matters that it’s failed - Euro indeed does split to 50hpa). The combination of downwelling weaker zonal winds and the location of tropical convection could produce an exciting second half. Moral of the story, we may need more than one bite of the cherry but I think we go from a U.K. high to something better rather than worse.

5.6, 91mm

See the post just above yours, yes. With 14 out of ~300 years of records it's about once every 25 years.

The Jan spell was almost definitely the SSW response. The timing is about right and you can see even on the European archive that there's a -AO which develops, just not near Greenland as much. We also saw a very blocked February around the UK which is again very common in weeks 3-7 for the UK after a SSW. The stratosphere was not especially weak during Feb/March which suggests it wasn't directly responsible albeit the tropospheric vortex may well have still been shredded from it. It's not a radical change in the overall forecast, comparing the charts it looks like we've simply lost the very deep SSW forecasts and so the mean has risen a little higher. We are also seeing the warming right now so it's perhaps a little weaker than expected.

While not beneficial, it's not the strength that is really an issue currently. Most moderate to strong Nino analogues show a +AO December which flips for Jan-March. 09/10 is a significant anomaly for a Nino of any strength. We also had convection in the wrong place until about the 20th (feeding through around months end) so we may just have been unlucky in the tropical cycle.

20DEC2023: Nino3: 2.1 , Nino3.4: 2.0, Nino4: 1.4 Yes. 3.4 is stronger than 1.2 but 1.2 is still +1.6 so its basin wide centered in Nino 3.

Too quick. A quick response is like a week or so, that's almost symmetrical.

I'll comfort you all by pointing out that the long run impacts of a SSW are limited and so late winter SSW's are those which are correlated with a cool March and April (the link extends to May as an average but it's a long time since a Feb/March SSW year had a cool May). Analogues for a SSW between Jan 1st-16th (excluding double SSW years for rarity).. 2021 - Near average March, Cold April and May 2019 - Warm March, near average April and May 2013 - Cold March, April and May 2004 - Near average March, April and May 1985 - Cold March and May, near average April 1977 - Cold March and May, near average April 1970 - Cold March and April, Warm May 1968 - Near average March and April, Cool May. 1960 - Near average March, April and May 4/9 March are cold as are average which is a little above the expected mean. The main signal here is warm March is unlikely. 6/9 April's are near average so clear signal here. 5/9 May,'s are cool interestingly given April's signal. .. Obviously we want to know how many cold Jan and Feb. Jan - 4/9 at 3.7C or below Feb - 4/9 So above the mean chance

Yes. Somebody provided us with the chart earlier but this chart is key to demonstrate. So basically as you can see here, even without the SSW on the right, the warming earlier in December caused a downwelling weakening of the zonal winds (albeit not enough) which can on its own be enough to produce a significant tropospheric impact. In Jan 12 a failed SSW produced the coldest first half to Feb in some time. Last year, the reduction from 50ms to about 10ms in late Jan was enough to flip the pattern to high pressure even if mild still. It's hard to tell exactly what mark you need because to some degree it will also depend how hostile the troposphere is so not all events will be the same but our push from about 40ms to about 5ms or below is a good strength push and is likely enough to produce at least a pattern change even if not snowmaggedon.

While your correct to be skeptical and most people on this forum do get far too giddy about the next Feb 47/March 13 oncoming, in this instance I would suggest that there is a very good chance of the second half of January being the coldest since at least Jan 21. Even if a SSW does not occur, we still have a 30ms+ reduction in zonal winds that will push down the atmosphere from early Jan and we should see convection leave the Indian Ocean around the same time to move into a more favourable tropospheric window even without stratospheric assistance. So i would not get too excited about February onwards as things stand and it's possible that the pattern change is simply to a cool mid-lattitude high near the UK but at the very least the background drivers don't really support sustaining zonality past the first third of January.

Most of the time but not always. It’s simply the vortex being pushed around on this occasion.

Three SSW clusters in that first third, the mean avoids it but largely due to spread and the strongest SSW is probably the highest plurality.

Just curious where the second U Wind anomoly chart can be sourced.

13DEC2023: Nino3: 2.1 , Nino3.4: 2.0, Nino4: 1.4

They were very different years even allowing for warming so I don't think we have to allow a substantial discount to 2022.

It's at ~17 Degrees south so very tropical. Basically in Venezuela.

Modelling currently suggests that we flip from Nino back to Nina. -QBO is likely to flip towards +QBO by end of year. -PDO is likely to persist IMO. 2010 and 2022 seem to be the best analogue matches of recent times.

As the second chart shows even if we end up with a SSW (we don't on this but it would just be a darker blue), it will still be January when it's reached the troposphere. Thus we are as you say dependent on tropical convection but since it looks like we will miss the boat on on the late phases. Current convection suggests we might persist somewhat into 2-3 but the Indian Ocean is normally not our friend.

Still here. Tamara knows more than I and summed up the pattern earlier but essentially my take is that tropical convection is in/moving into a position conducive to blocking to our north east and then north west but bar a poor looking northerly attempt it looks like the tropospheric zonal flow is too strong. We've missed the boat on this tropical cycle I think however it does look like there might be less tropospheric zonal flow and a conducive tropical pattern towards mid January.

SSW or not (not in this case), it's interesting to see that the weakness does actually propagate down. Remember that Jan 12 failed to achieve an actual SSW but the hit was enough to give us the first half of Feb 12.

Interestingly it turns out that the two most likely periods to produce a SSW are 1st-10th January and 20th-28th February. GFS0z operational got as low as 8ms today but the GFS ensemble mean to 1st Jan was still 20ms. 37% of Euro ensembles do get a SSW between the 7th-29th January (only 17% during week 1 of Jan now) but as the mean is actually rising, I think that's noise. So my message is essentially that it looks like we don't get a SSW during early January.

Low is still weak so while it may rain for a long time due to track, it probably won't be that heavy.

Anything last March. We got 15cm.