Put it this way.  It was the last straw that broke the camel’s back.  But if you take off all the other straws and then place the last one, will the camel’s back still get broken?  No because it was the combined weight that broke it!   The simple fact is that all the pieces didn’t fall into the right place to give the desired weather. 

I’ve still never really understood the NAO index. I mean, I know what it represents, but is it set so that zero is “climatically average”? If not then of course you would almost always expect it to be positive, simply by virtue of the default pressure patterns on this planet. If it is, however, then those stats are quite impressive/depressing. 

I mean, negative NAO doesn’t actually mean the pressure is LOWER to the south than to the north, does it? It just means that the positive differential is smaller than normal? For such a seemingly simple measure it is amazingly hard to find a definition of how it is calculated!

This could be wrong.. but I believe they measure the pressure between the Azores and Iceland. The standard pressure for the planet is 1013.2mb. So if pressure is lower than that figure to the north we are in a positive phase. 

With the Azores high I’m not surprised we are nearly always positive.

The NAO reluctance to switch to its negative phase with such a strong -AO is a bit of a mystery this winter.

A settled 10-days ahead looking at the average pressure slightly lower in Scotland but no washout by any means. Mild as a result widely across Europe.

I don't think there is any mystery. Unfortunately, the most vigorous polar vortex remnant took up residence in eastern Canada - always the least propitious location for European winter joy. Any attempt at ridging towards Greenland was swiftly deterred by nasty shortwaves spewed out by the vortex of winter doom in Canada.

For European cold, we need mild weather across the Pond without the nasty vortex taking up residence in its preferred location.

I know its very early to call, but i really think we are now entering spring.  I think the outside chance of a few cold shots, but the feel outside this morning.  The charts are showing a very dominant massive HP over europe - with LRFs also aligning to this mindset.

Ive seen some snow this winter.  move on.

Yes!  And I know I have a wax problem.

It is a remarkably rapid and large rise in pressure, isn't it? (With acknowledgements to Doc who made a similar point.)

The NAO simply measures the pressure difference between, roughly, the Azores and Iceland/Greenland.  Yes, the climatology is low pressure to the north and high pressure to the south, so you'd expect the default to be a positive value.  Of course the larger the number the greater the west-east flow.

The point of that tweet was that there hasn't been any sustained blocking in the Greenland/Iceland area during the last 8 Decembers and Januaries; when we've seen blocking at all it's been at the tail end of winter or early spring (i.e. February and March).

Edit: link here: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/history/method.shtml

I believe your interpretation is correct, that it's measured relative to the climatological mean pressure (probably for that month of the year rather than for the year as a whole). Otherwise a negative NAO when averaged over a period of a month or more would be a rare event, rather than occurring 50% of the time when you look at monthly figures over a period of many years, as graphs of historic NAO suggest.

Wkipedia has quite a good article on it, though even it isn't 100% clear on the point at issue.

I was just wondering as we went from easterly QBO to westerly. So i anticipate that perhaps the intense cold weather 'polar vortex' in N. America which was responsible too for ruining our chances to develop HLB as it amplified the jet!? 

Ok well a two years ago today we had daytime maxes of 2c with snow flurries and light snow on  Sat11th Feb 2017 - This easterly occurred when we didn't even have a SSW:

Yes me neither - like what does the -1,2,3,4,5 or +1,2,3,4,5,6 mean?

a couple days ago the AO was crashing with some ensembles  going down to -6 - what ever this meant? But look at the most recent one?

Same for the NAO:

My guess is that if the GFS op run was like today's 00z Para run which shows quite a block from +300 - then we would start seeing these ensembles going into negative territory!? Or have i got this wrong and the NAo index is not based on the model outputs?

The odd thing is, the 0Z GFS para has one of the coldest FIs this winter with widesptead -12 to -14C 850hpa temps. There is still a suggestion that a greenland high may try to form. I'm not saying its likely but it may be premature to completely rule out a return to winter yet.

Parallel has always been the coldest out of Operational and Control runs, so Yes agreed! - seeing as the Parallel will be the new operational it's usually the GFS op run thats crap but the parallel is no better because whilst it's been the coldest of runs it's been the most inaccurate and I remember when we were due an easterly end of Jan the GFS and flipped to mild whilst the parallel still wanted to keep that easterly from 22nd and 23rd Jan up until a few days before.

Most recently i remember up until Friday the Parallel run had many parts of the south and south west covered in snow for Sunday (Yesterday) for snow cover - well we all know that never materialised! 

We have seen some early 'final warmings' of the polar night Jet this past decade so maybe the current 'stretched' vortex has placed portions into the returning U.V. and so begun a warming.

The 06z GFSP and several of yesterday’s were not cold compared wi the suite and re. The snowcover many of e models showed snow in the south for yesterday, not just tthe GFSP. For example Saturday’s ECM 00z run had this https://weather.us/model-charts/euro/2019020900/united-kingdom/snow-depth/20190211-0500z.html 

Admittedly not that much and not really in SW but even so it goes to show. The GFSP op run quite consistently showed the January switch to colder more unsettled conditions from a couple of weeks out. It is not the best model out there in terms of details or consistency but from what I have seen it is certainly not the worst. 

Then this confirms above the parallel has flipped from 00z being cold and blocked to 06z being milder. SO the latest GFS06z para was good confirmation to support your honest and true comment.

So you’re saying it is not good because it is consistently cold (which is not the case in recent days), then you confirm this by saying it is not good because it’s not consistent? Which is it? Secondly at days 5 and 6 its verification stats are higher than the existing (soon to be replaced) operational model.

I was confirming that what Moomin said was largely correct in terms of the fact it's unreliable:

"It strikes me that the GFS parallel is even more unreliable than the operational. It's been pretty much a wintry nirvana since December. Clearly it's a load of crap."

Meanwhile the Met office Glosea 5 seasonal mean outlook has been updated and this is quite an almighty flip from extensive northern blocking to extensive southern blocking esp over Greenland which shows then that this blocking was due to occur in February!?

Last month's:

The very latest updated today:

Don't know how anybody can defend the MO for our region.

The stats are misleading, because they are for accuracy across the hemisphere.

If you look at the regional picture, our poor, damp corner has consistently been the region with the most uncertainty and scatter in the model output.

This winter has not been a good one for the NWP as far as NW Europe is concerned. As for Glosea - belongs in the dustbin - it could not have been more consistently wrong if it had been deliberately programmed to be so.

The uncertainty is to be expected in a region where small differences can have large impacts. It’s not a “fault” of the models which needs defending, it is a feature of our temperate maritime climate. I suspect hemispheric patterns are a bit easier to spot than will it snow in my metaphorical back yard (the British Isles) situations.

A cold and snowy winter may not have had any more reliable model output the difference is that not many would have cared.