Mike Poole

That’s a big question. What is wrong with the GFS? As I’ve some of my beer left, and nothing else to do, I will try to answer. The GFS has had several upgrades recently in terms of model resolution, vertical or horizontal, and none seem to have given it a gain over the GEM, let alone the UKMO and ECM. I don’t think it is the model, I think it is the procedure / algorithm for calculating the position at T0. Data is collected at various times and in various places, and the model needs to get the best possible understanding of the whole atmosphere at T0 for the forecast calculation. And that is a very difficult mathematical problem, called the ‘inverse problem’, determining what T0 conditions would have best come from the observed data at different times. The UKMO and ECM tackle this using state of the art maths (called 4DVar) but GFS fudges it a bit, so it doesn’t do it as well. It is a chaotic system, so if your initial data is a bit rubbish, no amount of extra model resolution will sort that. Ironically, this might be the reason why ECM is wobbling a bit. We’re lacking flight data at the moment, which is time varying, the kind of thing the 4DVar is designed to cope with - data at different times, it may be that the current data available to to model initiation doesn’t benefit the ECM as much. Just my take on it, of course, and happy to be corrected.

The parallel GFS has much higher vertical resolution than the op GFS. This may not matter much most of the year, but it does matter now, why? Because the SSW on 5/1/21 is a major player in this and will be for at least a month yet, so the higher resolution in the strat is definitely an asset to the new version.

Had to crack open another beer for the // pub run! T372: The gift that goes on giving. Phase 1, get the cold pool in via optimum alignment of Atlantic ridge and Arctic high. Tick. Phase 2, establish a blocking high in a more or less perfect position to get maximum draw from that cold pool. Tick. Phase 3, just keep it coming. Tick. And while keeping the high pressure far enough away that snow can happen. What a run!

One more from me, T342: May end up a wee bit north but whose counting at that range, T850s: That purple thing could be licking Nicola Sturgeon’s backside.

GFS pub run // T300: Just WOW!!! Goodnight everyone! See you for the upgrades on the 0z suite...not!

Yes. It is as well to remember that in an uncertain situation that this most certainly is, prospects can go up as well as down! Am I trying to sell a stock market investment or something,

GFS pub run // going all in on Greenland high at T228:

GFS pub run // has the balls to go with it at T192!

GFS 18z // looking to slide the whole NH cold down and right at us. T174: Go the green member, but to get it erected as well as this is unlikely, it couldn’t really be any better aligned at this point, such small margins...

Sorry, but I’ve been quite bemused by this thread over the last day or so, all the talk of upgrades or downgrades is well beyond the reliable in a very uncertain situation. There’s hyperbole by some, who to be fair have form for that. But a bit of realism wouldn’t hurt, would it. It is a foggy road ahead and we can see the first few steps and they are now looking very promising, with the Atlantic and Arctic highs now virtually guaranteed to advect a cold pool to our east/northeast in a few days. That’s phase 1. And that looks solid now. Phase 2. Can we get a northern block in the right place to bring this in to the UK but sufficiently far north that there can be instability in the flow? That is still totally up for grabs but well within the envelope of possibilities. What more can you say, to firm this up it isn’t we need more runs, we need to be a couple of days closer to it to close down the uncertainty.

GFS 18z // looking very good at T126, connection with the arctic high and that troublesome low kicked aside to the SE. Lovely.

Well this is very early on T126, and we’ve got the alignment of the Atlantic and Arctic highs, and the cold is coming down, and the troublesome low looks like it has somewhere to go: Too easy? Or an absolute snorter? Keep watching!

ECM mean, T144 - good agreement on the atlantic and arctic high link up, and T240, good for northern blocking to bring the cold in: 12z suite in all, what’s not to like?

ECM is messy, will probably recover in last two frames due to the position of the high and the amassed cold out east. But it is a big move to the others from yesterday’s 12z, a lot more things go right earlier on. And a mid way solution between the big 4 would probably deliver now...

Cold barges on through regardless of the low it seems on T168, although maybe some detail missed in the 24 hr time step. And we’re cold:

Yes, it is filling though, could put a delay on it...macro NH profile still good:

All good T120: The link up is there with the arctic high, but as last frame, the block a little weaker on ECM.

Looking at arctic high, ECM actually looks closer to link up at T92 than GEM, shortwave not in the way, but the atlantic ridge is weaker That’s not the whole story of course, but it is where ECM 12z yesterday went off the rails:

Yes, just takes a bit longer on this one.

Great upgrades this afternoon. GEM is fantastic, GFS is very good, both have a clean evolution to bring the cold towards us in the day 4-7 period courtesy of the Atlantic high and Arctic high aligning well together, the // slightly less clean evolution. Massive ECM tonight after the last two rather disappointing runs.

The fact that the Arctic high has such an important part to play in the period T120 - T168 is probably making it difficult for the models to see the way forward beyond this point: The models find Arctic high’s difficult.

I don’t think it does Si, look at the arctic high, it will cut off the cold like the ECM.

GFS // pub run - in a parallel universe that has pubs, T168 (1 week from now): I say again, the interplay between our block and the arctic high is crucial to how this pans out, and this run went well with a continuous cold feed over 1000 miles plus. The normal GFS run in FI is absolute nonsense in my view.

GFS // T132, and again on this run long fetch NE - see the 1030 hPa line in yellow, going to be a good one:

Better linkage between the burgeoning high with the arctic high at T114 on the // compared with T120 on the 12z: