Mike Poole

Surely the key question is whether the two Highs merge and the low to the WSW goes under,looks like this will happen to me T90

I think this one might be going the right way. GFS at T66

Yes all looks good at T75 This run only goes out to T120 so we probably won't learn much more until the GFS.

I'm fascinated by this potential cold spell. I (like many others I'm sure) have been following the model output since the SSW was forecast at the beginning of the month, and by today found myself giving frame by frame commentary in the MOD thread as the epic ECM 12z rolled out (not usual behaviour for me!). After today's 12z output and the Met Office views, I'm confident that something interesting is afoot. But what? There is in my opinion now say a 40% chance of a quite significant cold outbreak - and given it will stretch into March if it happens, it could make March 2013 look balmy! Very interesting times,let's see how it plays out. (mods - meant to put this one in the cold spell thread, not sure why it ended up in here (beer possibly responsible!) please move if it's off topic.)

To those pouring cold water after this epic run I would note that a) this evolution starts at T72 - if the worlds best model has this wrong at that timescale then we may as we'll go back to tea leaves, seaweed and witchcraft, b) it has Met Office support and has had for a while, c) it is consistent with expected evolution after SSW and d) OF COURSE we know that the latter half of the run is just for fun and probably won't verify - but what if it did?

Did someone mention retrogression?

T192 heading towards epic territory Detail still to be ironed out but the basic cold evolution in the early part of the run nailed surely?

T144 Have I got this right, that low WSW of Spain should go under and prop this lot up?

T96 Could those Highs link to form mega Ely pretty early?

ECM looks Good at T72

ICON still going with it

A mystery thus far why the ICON has been so consistent - probably the 18 will go the other way! But it is a different sort of model, in that it has an icosahedral grid. Another such model is the FIM, and the 12z for this model also develops an ESE flow at T 144. This is the most addictive period of model watching since I took up this ridiculous hobby (Dec 2010 was before my time). I'd like to take this opportunity to thank the knowledgable posters on here for their expertise, humour and stickability. Go netweather!

Inclined to regard the ECM as work in progress at the end of the run. 850 temps not that cold yet. But look where the airs coming from! This saga has a while to run yet.

Would you Adam and Eve it. ECM at T144

I think that if the UKMO isn't correct here, it must surely back down on the 12z. Won't it? Looking at the verification stats for T144, for the last week or so - either side of the SSW, the UKMO has been right up there ahead of both GFS and ECM - whether this is significant or not, we'll have to wait and see. Stats for 0z and 12z:

Was that the Dec 2012 one? I'm remaining upbeat as we head towards the 18z, the 12z ensemble was still good for Greenland blocking but given the timescale we wouldn't expect every op run to go in the same direction. GEFS mean at T324:

Ooh yes, that does look fun!

Before the 12z's roll, I' m considering the question: 'are the models struggling following the SSW?' I say NO. Virtually every run from every model that I've viewed since the SSW has had an evolution towards a UK high this weekend, and that high then migrating N, NW or NE into next week. Even beyond what we would normally call the reliable, there is still consistency. Trouble is, exactly where the block sets up matters greatly from the point of view of snow for the UK. And this can't be resolved on the next set, the 18's, tomorrow or even for a few days, we're expecting too much from the models! But that won't stop me watching the 12's!

The models will take it in their stride. It's common misconception that I've noticed on here - that the models are somehow programmed with an envelope of expected evolutions and struggle with extreme evolutions outside of it. They don't work like that. They simply take the best guess of the state of the atmosphere at the start of the run (T0) and then simulate their best approximation to all the laws of physics that affect the atmosphere (or atmosphere and oceans in the case of the seasonal ones e.g. CFS) for the length of the run. So the fact that the world is warmer than it used to be is irrelevant.

The 12z op runs seem to have been taken as a downgrade by some, but I think this to to fail to see the wood for the trees. What the excitement about yesterday was all about the strong signal from the ensembles to progress to a Greenland high on 8-12 day timescale, consistent with expectations re the tropospheric response to the SSW. I've said this before but at the moment the destination seems clearer than the route we get there so the individual op runs are maybe not the best guide until we get this cold spell into the reliable timeframe. GEFS ensemble mean still looking very strong for Greenland high, 1045 countour on this one at T336

The GEFS mean at T+336 I don't think I can recall seeing the 1040 contour on a mean chart beyond T+300. This is a VERY strong signal.

GEFS 06z seem to show an evolution to a Greenland High via a UK High. Taken as a set, plots below of probability of pressure >1030 mbar: Leading to this mean at T+348:

Hryggur in this context means 'ridge' - Atlantic ridge presumably, not 'sorry' which appears as the primary definition on Google translate. I take the coloured border of those plots to be indicative of the wider pattern that you can't see - may be wrong. In other news, the SSW appears to have had a strange effect: Oh dear!

I think this might be one of those occasions where the destination's clearer than the route to which we get to it. Here's the probability of >1030 mbar at T+192 All across the UK, but by the end of the run, clear high latitude blocking Suggested towards Greenland These probability charts from meteoceil are good but why are they just shades of blue? Surely they should be in glorious technicolor like the rest of their charts! Anyway, it looks like we're on a road to somewhere.

So, where are we now? Let's consider probabilities, I think the original position, stated by someone from the Met Office was that a SSW would lead to UK cold 2/3 times - 66%. Add on to that that it's a big split SSW not a displacement, maybe put that up to 75%? Now that the models will have reasonable representation of the state of the tropospheric conditions at the time of the SSW, surely the 12 z's push this up to maybe 85%, particularly the ECM. Finally a look at the GEFS Chart shows probability of surface pressure >1030 mbar - Safe to say. It's pretty much all to the north of the UK at T+324.