Trom

That big blob over Sheerness has got me excited for South London/North Kent and Surrey

Those blobs hitting South End look to be on a line that could hit South London - depends whether they can hold both direction and intensity.

Fingers crossed James

I'm crossing my fingers. Does look like the shower movement is becoming more Westerly. Showers not far away from my little red dot on the map. 4th consecutive sledging with the kids today so the Croydon crew have done pretty well over the last week. One last little top up of the white stuff would be nice. Guess I'm going to be chasing showers on the radar for a couple more hours!

Given the amount of snow we've seen it could have been so much better if those ground temperatures were lower. The amount of hours with falling snow has been huge in this area but never huge intensity. I suspect we've done better than many with the exception of parts of East Anglia and Kent.

We've done quite well since Sunday in the south of the Croydon area. Plenty of sledging and fun with the kids in Selsdon Nature Reserve and Lloyd Park. Looks like the ENE is giving us a little pep from the Thames and we also may do well as the winds veer more easterly. Certainly a little lucky as we've been on the western edge of things.

In the first week of Feb with ongoing stratospheric disruption? I think we will see on going weather that defies the climatic norm. That's not to say epic cold until mid-March.

The reality is that even the good runs have milder air not too far from the South. So I expect it will be a yoyo ride for the SE run to run depending on the speed and track of the low pressure feature. Further north and this is less of an issue.

Yes RMSE is the standard deviation of forecast values around an actual value for out of sample data. Lower means greater predictive ability.

Slightly different phenomenon same end result!

Looks to be sleety away from Wales. I think the orange hatching is sleet, is it not?

Each of the models is a set of fluid dynamics algorithms. No two models are the same algorithm. The major differences can be explained by: 1. Different starting data (the data is not perfect) 2. The set of algorithms 3. The resolution of the model (essentially they divide the globe into boxes, with each box impact the boxes next to it and so on). More resolution = smaller boxes. Due to the issues with incomplete and sometimes errant starting data the models also run ensembles. These tweak the initial starting data to see what impact it has on the model over its run. Hope this helps

I think it's worth noting that day 20 (sorry 20th Jan) is actually only 14 days post SSW. This would be a very quick trop response to downwelling. So I'm still hoping for better synoptics in future runs. Plus we have continued warming events in the strat. Nothing's guaranteed but it should be an interesting journey into Feb. Edit Not to say we're not seeing a response to the SSW just that it's still early days.

All seems very bullish on here today. The phasing or not of the two lows seemed extremely tight and led to very different medium term outcomes i.e. UKMO vs ECM/GFS. It really seemed razor tight whether they phased or not. I'd like to see a little more separation on the 12Z runs to be confident. Additionally, as usual, there's been a lot of cognitive dissonance, in dumping runs that don't show the preferred outcome. Of course this is a human nature, resulting from conformation bias. We all seek information that confirms our desired result and have a bias to ignore information that doesn't. I'd feel more confident if it was the same model being dumped in each run but it's not, each model seems to have moments as a hero and villain at the moment. So I'd advise a little caution moving forward until we see some intra run and cross model agreement on a more consistent basis. Fingers crossed - I'd love some snow as much as anyone.

I was talking about the operational run. ECM = 137 post June (91 before June 2020) I believe the ENS run with 91 currently

I can see the argument that the GFS(P) has more vertical levels and theoretically should be able to model the events in the strat more accurately than the existing GFS. However, it's worth remembering that even the parallel has marginally fewer levels than the ECM. So for those hanging their coats on the parallel, I'd be looking for some agreement from the ECM before climbing aboard.

I do hope you are right. 14 days is on the quick side. There's still a lot of short and mid term volatility. Might take longer and a second attack on the strat vortex (if we are to get deep cold). There seems to be traction on lower heights to the South of the UK and ridging of heights into Greenland. The ensembles tell a mix message on all models which is unsurprising given the flux and the lower resolution and adjusted input data. Happy to see the operationals move in the right direction but I wont feel confident until the ensembles can back it up and we get more inter-run consistency in the relative short term. Keep them fingers crossed!

Turtles can have a nasty bite

Yes all a bit despondent in here tonight and I'm not really sure why. Some good posts showing how the models failed to get a grip on 2013 and 2018 at this range. Also some really good indications of cold to our east. No two SSW are the same and given we've only really been looking at them seriously very recently there is a lack of training data for the models, which in turn makes any mid-long range forecasts dubious at best right now. This is an important point - without training data i.e. enough evidence of how multiple SSW have unfolded in the past you can't train the algorithm to predict with any reliability. This should get better over time but remember they are still rare events. I've been encouraged by seeing strat models pushing the vortex over Asia and the Atlantic initially but then pushing the real cold back to Europe later on. As yet nothing we can pin our hats on but very much all still to play for! Keep those fingers crossed.

Yes I'm looking for proper cold to our east, and there are some early signs of that with the trop vortex (daughters) forecast to move over Asia and Europe. Then we need the conditions for an easterly or north easterly and we are in proper business with no more marginal. So I guess we wait for the models to form a consensus on the mid-term direction of travel. As many of us have said over the last few days, the models struggle with a situation that is so rare. Put simply, the training data is sparse for these events, so while the models are getting better on the detection of these events, I'm not so sure they are on the impact. Lets see and cross our fingers.

Yes I'm just down the road in South Croydon with slightly higher DP of 0.6. Looking at the radar and trying to extrapolate the stream coming in from the NE, looks like we could be clipped by some wet snow or sleet but it looks 2 hours way and not intense. Good news is that the cold to our east is likely to increase given the SSW predictions. All we will need is the easterly in 10 days + time. Fingers crossed.

Cool that what I thought you meant but I was confused with the wording. Yes I'm hoping for an Easterly as it now has much better prospects with that cold to the east. Whilst it's not showing in the models, I think we will have to put up with volatility in the near and mid term as the models get to grip with the trop impact of the SSW. So fingers crossed.

Doesn't that show a large pool of cold forming further east? Are you trying to say that up to now we haven't had a cold pool to tap into with an easterly but that's changing? If so that's not how your post reads.

This image of the warming shows the cold being pushed into Asia and Europe (green blobs) So cold building to the East!

What I don't get from that is that it states "whether this source is untapped in operational models remains an open question" and then states "The ensemble forecast from 8 February predicted the SSW, its subsequent downward influence, and a long-lasting cold anomaly at the surface" So to me that says the operational runs didn't show the impact of the SSW but it did show up in certain ensemble runs. If this is the case how do you know which ensemble member is correctly modelling it? I'm not trying to argue with you but simply trying to understand what they mean in this report and how it impacts on our ability to actually read the models. It still seams that most of that paper is about the ability to forecast the SSW and not it's effects. It also states "the SSW's downward influence was not well forecasted". To me this says if you looked at the operational run it didn't correctly show the impacts but if you looked at the ensembles and knew which one's to choose you could see it. So it all looks a bit hind cast to me. But what I think what we are both alluding too is that this is an emerging area of modelling which will only get better with each event we witness. I'd also like to say it's a pleasure when somebody who disagrees with you brings new information to the table. I also hope you get to see some canals freeze over like you did in 2018. It was the first time I'd seen some canals in Amsterdam with ice on the top and the first time my Dutch friends could remember since childhood.