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Morning! If there is one thing that sums up the current state of model output it would be the following…. Yup it’s at a crossroads and this is particularly fascinating as I will go into some technical detail below and how this is relevant to the model output. Hopefully this can be clear to other members and it will give an idea of what I am looking out for. Background So, first some context…. The UK winter is moderated by the Gulf Stream, warm ocean currents move north from the tropics and help prevent the UK from being as cold as somewhere like Moscow. The diagram below shows a picture of the ocean currents. Warm air directed to the UK from Gulf stream Now interestingly there is evidence to suggest this is slowing down which generally should mean a negative feedback in the northern hemisphere due to a decrease in heat transport. Just one problem… the strengthening of mid latitude highs and deepening of polar lows means the Eurasian continent has warmed substantially during the winter months. Trends in SLP since the 1950s (Gillett et al 2005) So where is affected by this negative feedback?, well the below diagram clearly shows one place. The central North Atlantic. Looking at warming trends in the figure below we can see that this region has actually got cooler over time, in stark contrast to almost everywhere else. IPCC, global temperature trend from 1900-2012, spot an anomaly? This is now referred to as the North Atlantic cold blob and I believe it hurts our chances of cold winters. Look at the last 4 winters. These have been dominated by more frequent then usual westerlies and the North Atlantic SST profiles are seen below. 2013/14 2014/15 2015/16 2016/17 February 2018 - See a pattern developing here? To get a cold anomaly in this region it requires cold air from NE Canada to pour into the North Atlantic…. And how is that possible? Yup with a polar vortex camped to the west of Greenland. So with a slightly weaker AMOC and an intensification of mid-latitude highs we have a pretty poor combination of factors for UK cold whereas in the US it ain’t so bad. That is why the US still sees these big cold air outbreaks from time to time. So how can we break this sequence? Well other factors also influence our climate, extreme MJO phases, low solar activity or a dramatic slowdown of the AMOC can do it. In December 2009 this is precisely what happened. With the increased warmth nowadays, if this is directed to the arctic it can really shunt the PV for long periods of time. Just look at the anomalous arctic warmth in 2010. December 2009 - Bullseye Indeed this pattern persisted until January 2011 but a very strong La Nina signal prevailed for that winter later on. Other alternatives are extreme MJO phases (the phase 7 signal recently helped build Scandi highs to our east, though they weren’t that strong) and deep cold pooling just to our east. However the warming arctic and more intense mid latitude highs makes this more difficult. Just look at the last 4 Februaries + this January and their temperature anomalies. Continental cold can stop the Atlantic in its tracks. In 2013 we got lucky and February the arctic was actually colder then normal. This cold air spilled into Scandi and in combination with the SSW event, this was allowed to stem the Atlantic tide and as a result we got a very cold March. Battleground in the model output So where does this lead? Well its of my opinion that we are seeing a more volatile NAO because positive phases are amplified by trends in mid latitude highs. Negative phases are amplified by increased warmth heading to the arctic. Just look at the NAO values for each winter since 2006. 2006/07 + 1.81 2007/08 + 1.34 2008/09 - 0.31 2009/10 - 2.71 2010/11 - 0.84 2011/12 - 2.08 2012/13 - 0.58 2013/14 +2.05 2014/15 + 2.04 2015/16 + 1.84 2016/17 +1.12 Bear in mind any mean value over one is considered extreme So Yup we are at a crossroads, will the organised polar vortex drown out the SSW again? Will there be more cyclonic westerlies? The current SSW event is fascinating because of its location shown below. Additionally if the pendulum swings the other way then we could see the strong negative NAO months make a return with an exceptionally warm arctic/Greenland. It seems conditions are becoming increasingly favourable towards the cold air in the North Atlantic persisting in the winter months and more factors need to come together to overwhelm it. We came so close early on in the winter and if this had succeeded then the winter NAO I believe would have turned strongly negative. The critical point highlighted below. I believe the struggle to overwhelm the North Atlantic cold pool is what is leading to some of the disappointing runs from the ECM. Will we succeed this time though and cause the see-saw to swing the other way? I believe if it does, it will help next winter too. At the moment its hard to tell, the ops look poor but ensemble means are more intriguing. GFS ECM Hope you enjoyed reading my thoughts and have an insight into what to look out for in the model output! This is an educated guess but it is what I believe. Quicksilver

Looking at the 00z EPS clusters, although are 6 clusters as early as day 8, 3 clusters comprising over 60% of the ensemble point towards ridging building north from 18-20th. EPS clusters: http://brunnur.vedur.is/kort/ec-ens/2018/02/12/00/ec-ens_nat_z500scenarios.html The more positive shift overnight by EPS to offer more blocking with Ely or NEly solutions developing in the last 8-10 days of the month could be related models perhaps not capturing correctly the likely impacts of the SSW prior to the event, but now the SSW has started happening, the models will start to adjust to showing more blocking in the NAO domain now they get a clearer picture through new/recent satellite data of the downwelling of the wind reversal. 06z GFS op was a warm outlier from the 18th, so expect to see some colder operational runs popping up. Given the enormity and duration of the stratospheric warming over the N Atlantic, it seem likely the warming will imprint in the troposphere over the far N Atlantic and areas bordering too, given the existing wave configuration in the NAO domain and that the trop PV will be pushed aside from Greenland. And for those worried about how late it will be in winter if/when the cold Ely or NEly flow arrives, take a look through March over the years and spot those that were cold and snowy, a good few examples there, even fairly recent, that show you can get ice days and big snow falls that can stick around even in March: http://www.trevorharley.com/weather_web_pages/british_weather_in_march.htm

OMEGA ALERT !!!!

The GFS mean ( & the GIF mean avove ) show a classic reversed zonal flow out of europe - typical of a strong negative zonal flow - In terms of the last 40 years you could probably count less that 10 sub -20M/S zonal means ... & probably 5 or less -30M/S zonal means.. Yes 5.... in 40 years. Frame it -37M/S...

Can we just agree that the first person to say it’s a dry easterly gets a life ban? opportunities endless, stunning

back by popular demand... appearing on a screen near you... Winter! starring - blocking! tonights episode... the beast from the east!

I obviously can't speak for Ian, but I'd suggest he's referring to the point in time where there is currently considerable divergence and the general thought is that this is due in part to the models acting upon SSW influence and increasing entropy values. Not certain, but it's a reasonable position. Naturally, as one progresses through time, you would expect convergence as depth of data influences the direction of travel with attentive entropy moderation. I'd still wager on a colder synoptic developing - I don't think the question is so much about that - it's more the degree and duration which retains uncertainty.

Getting there... Better and better. We can see you ECM, doing a 'nobody noticed, I think I got away with it' GFS style manoeuvre...

Another absolutely stunning ens set. This is becoming a very strong signal... This whole QTR debate. It has become increasingly evident (IMO) that the MJO / projected AAM was skewing things on the output and the SSW wasn't ever really being factored in. Well it was, but I don't believe it was ever actually forecast to propogate down that quickly. A good call by the models by the looks of things. And 2 weeks is still a fairly QTR as well. That said, a slight sub tropical nudge may be enough to get the MLB to turn into something a little more mouth watering, before the main event. All to play for. Fantastic model wathing days.

The differences between yesterdays T216 hours versus today’s T192 hrs is even more embarrassing for the ECM. Has Arsene Wenger taken over as CEO of the ECM? PS I’m a disgruntled fan before Gunners fans berate me!

for a bit of extra interest, this latest fax chart for this Friday could produce a surprise for parts of the south. The developing low looks to be close to the channel and any heavier precipitation may turn wintry as the air to the north will be quite cold with a mixture of low level surface air from the near continent mixing the colder uppers over main land England. Note the 528 dam still in place to the north of the low. Just an outside chance but one that may produce a surprise in the nearer term. C

I put out a tweet to Ian Ferguson. He’s replied they are looking around the 18th still to see effects. Plus this from MV gives hope

It’s frustrating that the models are finally converging on the idea of making us wait for high pressure to build far enough north to advect deep cold our way, but there is certainly a strong signal still from GEFS and EPS H500 mean on the 00z run for high pressure to build north over N/NW Europe past day 10. Day 13 GEFS H500 and you can see ridge building N while troughing is starting to undercut toward SW Europe with a -NAO signature evolving reading on a U.S. forum that increased upper divergence over Africa is a typical precursor to -NAO development and ties in with the MJO wave / enhanced convective activity progressing through 7 and toward / into 8 over the Pacific- despite RMM plots suggesting otherwise (esp GFS) MJO wave will try and build the high pressure north, but we also have SSW with easterly strat winds forecast for a good 10 days - which will surely help in building trop heights at higher latitudes of N Atlantic and N Europe. EPS mean at day 13 also with strong signal to build geo potential heights N, but further east over North Sea. Don’t throw the towel in just yet ...

So all it took at 6 days range was an adjustment in the angle of the ridge from the left to right charts: ...to turn Tuesday's situation from the left to the right charts: ...and that change became significant for what followed on the 18th which is precisely when IF stated there was important model divergence. Now here's GFS (left) v. UKMO (right): Very similar but UKMO not peeling away a little shortwave to drop down through Norway which GFS uses to add a little extra fire to the Euro trough. That could mean a gentler easterly at least in terms of wind speed in the 8-10 day range, but also less likelihood of warm air wrapping around the Euro trough and interfering with things in the 11-14 day range (never mind GFS' move to a west-based negative NAO and super-broad low 'scooping out' the Euro trough which is quite simply daft given the location of the peak stratospheric warming and height rises). Just as a side note - I can't recall seeing such a strong stratospheric high before as what keeps being modelled by GFS in the 11-14 day range. It's practically an anti-vortex! It's the result of not one but two strong warming events taking place on the eastern periphery of theCanadian vortex - truly fascinating!

cheers If you look at todays 12z suite its considerably more conditioned towards the strat effects over yesterday UKMO +VE height profiles over the pole @144 are 'abundant' to say the least- GFS &144-168 is the same - with polar heights mirroring the Strat split... A good PM suite coming...

Bonkers gfs run. From this to this in 3 days ?

I’ve been up the garden path that many times now Ive started naming the slabs ?

I don’t believe JH was of the opinion that any outcome would verify! And certainly not a mild one !! i suspect many in here are fed up of the chase and being disappointed- I urge you to get on board this time !!

Bloody hell burty ?

Oh and to answer the question "Why the sudden obsession with the D10-D15 ensemble means??" It's because historically they have been able to pick patterns when the anomaly is high. Couple of examples: 11th March 2013 - easterly for the UK picked by the D10 mean Perhaps one of the best was November 2010. Just a small resemblance to the latest GEFS charts for D15.

Finally getting there - note the spread on 850’s showing a push from the east by day 10 which arrives on our doorstep go on then - throwing in the heights to reveal where the highest cluster away from the mean sits by day 10 (not surprising given the 850’s). Now you know what to expect come 18:50....

Sometimes when the model output doesn't show what you expect it is best to sit back and watch awhile. Remember that the strat is normally a stable environment that is modelled well. But when we have a fragmentation of the vortex then the strat models will not be able to pick up where the remnants of the vortex will reside and this will be reflected with both the strat and trop output. So still caution advised but previous thoughts still remain regarding blocking and long term Scandi then NW blocking. There is obvious something in the programming that overreacted and reformed the trop vortex despite the fact that that would be against the background signals. If you turn off the hoover and someone says that it will still suck up the dirt then be sceptical. Likewise with the modelling.

The last time we saw an almost complete ensemble flip to cold was March 2013.. the time before that was 2010.. This is actually a good learning curve. Now we know the models will struggle prior to a SSW happening and then potentially flip to cold almost immediately after the SSW happens.

ECM is still woeful- Infact its going to get pwned by the GME ( DWD ) - Thats like Barcelona losing to a non league UK side Here is ECM 192 yesterday V 168 today Not that it really matters but UKMO has overtaken it as number 1 model in the last week (@ Day 6) but that is NH...

I suspect those of us who have been expecting the models to re-pick up the cold/Northern Blocking are looking at the 12z and smiling to themselves, I know I am. The GFS is a rather smooth transition to blocked and I think is probably going to be the most likely outcome. High Pressure building North-Eastwards over the UK and then we see undercutting from the East underneath the high, forcing it Northwards into a more favourable position. ENS/EPS picked this signal up in the last couple of runs, Ops are now smelling the snow too. Expect a cracking ENS set, the SSW has occured and these are one of the first runs to start picking up the full extent of it.

Well that was a bit like putting the kids to bed, got there in the end kicking and screaming and it’s left me a bit pee’d off, but now I can relax atleast.

Wow! Some big upgrades on the GFS and UKMO. We can safely say that the models aren't to be trusted before an SSW, its no coincidence that we've seen these changes post the SSW. I'd expect the ECM to follow these given its already made an embarrassing climbdown and its later output of previous days was destined for the cat litter tray.

The very kind Mr Fergusson just informed me of tonight’s ECM monthly output ... interest a plenty

Overall we’re moving forward at last . After slumming it for days at a one star hotel the ECM finally manages to book into the Ritz with a very good day ten chart. The GFS is much quicker to get to there. The UKMO also looks good at day 6. So after a tortuous few days for coldies things are on the up. Let’s hope this good trend continues .

still waiting on my 4cm by midnight like......... dont worry @hawesy 2 out of 3 aint bad

Sorry Guys, could not help this from the CFS .. its just so disgustingly , jaw droppingly good.... Easterly winds from Europe ploughing their way into the Labrador sea.. model porn at its finest

Just catching up. Fully agree with you on the ECM. After being a right misery yesterday I am amazed at the change on the output. Just look at the amazing GEFS mean!

GEFS and EPS starting to come together with the surface level Scandi High for D12-D14 Cold very near on GEFS (EPS a lot more scattered): GEFS then sniffs out a Greenland/Scandi link up - look at those isobars running east to west all the way across the chart!

Stunning set of GEFS at the FI end. Reflected here. Not often, if hardly ever, do you get a mean of 1030mb at the 16 day point in Reykjavik.

The joys of a spell 'working from home' allowed me to sample some proper snow down in the Badlands of the Ayrshire/Lanarkshire border (Glenbuck) today. The sprinkling at home melted when the sun appeared, and I'm expecting mainly rain and sleet tomorrow, although places with altitude should get a pasting!

@Hairy Celt On the back of what we were talking about yesterday this just popped up on my timeline from 9 years ago today. 12/2/09 and irrefutable proof it can snow in Crail. It just doesn’t choose to very often!

I think this could be a dry easterly At 276 and wowzer This certainly wouldn't be dry!!!

Certainly caught a few showers after I went to bed. Got around 8cm overnight.

To me, the lack of response from the modelling to drive and coherent response to the ssw until the latter part of week2 is quite clear. The gefs zonal mean for 60N shows the zonal flow in the trop doesn’t drop below average until around 24th. Clearly some members will do it earlier but note the sudden mean ridge build well north at this timescale. The ecm chart from Berlin beyond the initial drop in zonal flow to slight reversal (stays above 70N in the trop) shows westerly momentum above 55N fairly reasonable throughout and increasing later on. until we see the negative zonal anomolys getting to 60N (sustained and convincing) then any HLB is unlikely to be effective for us. We would be hoping to see these charts changing now that the ssw is underway as more members latch onto the change in momentum. Remember all ens are at lower res post day 10. (Where the eps drop). The gefs drop at day 8.

A rather dull and damp potter out by Cougie this afternoon. I should've gone this morning when it was colder and brighter. This one rather sums up the mood... This is melting snow and ice over the river... So... what fun will the A9 bring tomorrow? Some sources suggest a bit of rain, other more snow. We shall see eh, as ever. Oh, and the winter tyres proved their worth today - I got up a slope easily that a 4WD pick-up was failing on with AT tyres. The track had been scraped and the temp was fluctuating about -1C to 1C so getting nicely icy.

So lets Entertain the ECM evolution tonight ( inc JMA ) & put it into some context- because of overwhelming warming & reversal of winds we have GFS / Overall Mean / IKON / UKMO Versus the ECM / JMA I would day including background signals 80/20 in favour of the GFS blend - maybe slightly watered down initially. Remember my initial forecast from Weds last week was peak blocking 20-24, I think for me with the strat showing a double dip the window runs from 20-28 now with retrograde certainly at least a 50/50 horse ( 2.00 if you like decimal ) Lets get the first transitional high buttoned down first though....

3 in a row now. 1030mb mean. Closing in and sustaining. This is a strong & consistent signal. In fact, take out the op and the other 2 'rogue' runs and that mean would be even higher at the end

Here are the short ensembles and they're looking very good. Interestingly the Control and Op are on the milder side for days 7 and 8 Edit - and the Op is a gigantic outlier at the end of FI

Looking great.

And to back that up a little

At last we’re seeing some convergence in the models. Unfortunately they’re converging on a bit of a waiting game with the high not able to get far enough north at this point. As BA has noted you can tell by the ECM spreads that we’re seeing some solutions dropping some colder air south to the east which then gets advected west by day ten. Overall there’s now a bigger cluster of east ne flows showing past the 20th February in the ECM ensembles.

ITS SNOWING!!!!

Something is afoot, I've been posting stunning GEFS charts in the extended range for days now, I believe our (coldies) patience will ultimately be richly rewarded!

Like I said early afternoon, the NWP seem to struggle to model the effects of a SSW on the troposphere with any accuracy prior to the SSW event, but once the warming starts to kick off in earnest at 10 hPa as it has today, the models quickly adjust to showing the blocking developing as would be expected given the position of the warming over the N Atlantic and the wave pattern in the troposhere in place. Sometimes a case of knowing what is more likely to happen, based on reanalysis of similar SSW events against a similar background state (i.e. La Nina, eQBO, low solar + MJO orbit), despite the models prior to the event being all over the shop. Despite agreement of the blocking signal building over Nern Europe in 8-10 days, still disagreement between EC and GFS with regards to how far north and west the block will get and also how much cross-polar ridging there will be too. But the CPC prognostic 6-10 day and 8-14 day H500 mean and anomalies pretty much singing from the same hymn sheet with building the ridge north, though the ridge in the means building north looks further east than the 12z GEFS means And if you think the SPV will bounce back, think again ...

I must admit to liking these GIFS, now this is a classic cold spell if things pan out like this. High pressure moving west and remaining north of the UK throughout, easterly winds veering more north easterly as the high moves towards Iceland and eventually Greenland. Still lots of uncertainty but the general direction looks very good ideed.