swilliam

Jet in W Atlantic much weaker on this run as the PV stays W 12z 18z

More importantly everything is a bit further W - including the PV chunk over Canada that keeps gobbling the lows in the W Atlantic which then pulls itself further E

Also looks like Azores high might not link up with a small ridge there now

If you rock over the new frame and old frame on Meteociel you can can see that it is in fact (Currently at 108 old frame at 114)

More amplification off the W coast of NA which may hold the low back in the SE from heaading out to sea and interacting with azores high 06Z 12Z The low is deeper is well so my head further N

I remember it well - the GFS/UKMO were pretty solid then the ECM churned a couple of runs where the low that came southwards went SW and W based -NAO was shown. This then suddenly changed back again to dropping S.

Actually this was shown first on the 18Z GFS on Wednesday. I pointed out during the run that the initial ridge was too far W and thin which could lead to breakdown of the block at was then +240 (see below). This was the evening of the 1st stellar runs so I was then told by several people not to analyse every run, that the means were showing this etc. not to get upset (which I was not doing). All I did was point out what was shown and that we did not want this to become a trend. It confirms to me that no runs should be binned because we do not like what they are showing - just accept that they are one solution (especially beyond t120) which should be accepted as a possible if maybe unlikely outcome. the same applies when it is the other way round with everything showing zonal and then we start to see odd runs and ensemble members showing something different. Back to the current and as I see it the problem with the initial ridge being to far W and/or thin is that the 2nd surge of WAA does not really happen because of the orientation of the 2nd low in the US. So this low begins to head more NE instead of NW and interacts with the Azores low. This basically comes under the ridge instead going NW into the US. It is pretty much game over then in terms of prolonged cold for us although we my get a big snow event, However as has been said this phase is currently completely undecided and anything could happen at this stage so we will just have to wait and see. We can look at all the runs (good and bad) and see what the options are. But the main point I feel is that we want the initial ridge bigger and further E and then we want to see the 2nd low to rebuild the ridge rather than going underneath it. Impossible to call at this stage but the trend has certainly been to move more towards the latter this morning but plenty of time for change to the former.

Hope (and expect) that you are right - what a let down that would be.

Yes it is still pretty good but not as good as the 12z. I think this run just shows that it is still possible for it to go wrong. I am going to stick with the ECM mean and hope it is still like this in the morning. The GFS threw out a funny run on the 18Z last evening.

Well unfortunately there are quite a few supporting the OP as well.

err - they are the same?

Not sure why you have said this. As far as I can see most of the posts have been discussing the position and strength of the block, the depth and longevity of the cold and the usual where will it snow/rain etc.

Well as I had already put my head above the parapet once I thought I would risk it again.

Unfortunately there is quite a bit of support of the Op from the ensemble members - this is reflected in the change in the mean at 192 12Z 18Z Lets hope this is not a trend even though it gives a few days of cold weather still - as the Meto say - still a question on the longevity Sorry about the extra picture - seems to be bug if you make a mistake

Quite - looks rock solid till the 14th and then a few rogue members v. unlikely to verify. Then a bigger split around 17/18 which I would imagine is to do whether the ridge gets reinforced by the Azores low sliding up the W side of the ridge and reinforcing the block.

Yes - I am regretting making a comment on the difference the run was showing at an early time frame - I will not bother in the future.

No-one said it was a trend and no-one is getting upset - just commenting on the run. I said it was a problem if it became a trend.

Well I am expecting and hoping that it is not a trend - we will see in the morning.

That was based on the 12Z

Yes that is fine as long as it does not become a trend (i.e we something similar in the morning and then the ensembles show it more)

Looks a bit west based this one - hope I am not worrying too much - in any case it will be different tomorrow

Yes - if the mean goes below -5 then confidence should rise in the cold shot but of course we would like to see in a shorter timescale.

What was said was that if the mean is showing something close to the climatological average then it is not much use. If it shows a signification deviation from this then it is very useful. This is the case here

Shortwave alert around Iceland - holding back the colder air.

ECM mean looking pretty good at 240 850s at -6 in the North and -4 in Midlands