Its is "The Madden-Julian Oscillation (MJO) is the major fluctuation in tropical weather on weekly to monthly timescales. The MJO can be characterised as an eastward moving 'pulse' of cloud and rainfall near the equator that typically recurs every 30 to 60 days."

I understand it has little impact in Cumbria 

Thanks Paul and I suspect it doesn't have such a massive effect on the UK weather either but to read posts on here and NW you would think it was the be all and end all of UK winter weather!

All these new fancy terms in meteorology of which this winter has seen a whole new language is a diversion from what really matters and that is the upper atmospheric pattern including jet stream and ridge/through anomalies, both these parameters can change quickly and I am in no way convinced that they are dependant on all these newly discovered teleconnections.

Time to go back to tried and tested model watching I think.

Andy

Let's hope that GFS sticks with that theme this time.

Incidentally, ECM and GFS 00z runs are not that dissimilar at the T+240 stage, so here's hoping that ECM goes down a similar route over the coming few days.

Actually, almost identical. Very rare..

Sorry I didn't see the request sooner, the summary given by Paul is about right.

It's effect on the UK's weather comes as a result of broad-scale pattern changes driven by the effects of having enhanced tropical convection and anomalies of wind direction in the location that the MJO is in.

When the MJO is at low amplitude (i.e. weak), the impact is small, often hardly noticeable.

When it's at high amplitude (strong), the impact can be really very dramatic. A prominent example in my mind, albeit with the major ridge in the opposite place to where we want it at the moment, is the Sep/Oct heatwave of 2011.

The response depends on the MJO location, that being described in terms of phases of the MJO. That's where these composite maps showing the changes in 500mb heights typically seen during each phase come from.

There's far more detail that I could go into but it gets very technical and can cause hernias of the mind... I speak from experience 

Soon, the MJO is going to track through phase 6 in a strong state, heading for phase 7 in a weaker state and this is known to drive amplification of the pattern, initially focused in the western North Atlantic and then transferring more to the NW/N of the UK.

It's unlikely to bring about major blocking highs and severe cold within the next couple of weeks - instead we're looking for the jet disrupting, lows tending to stall and slide S or SE, and the chance of marginal snow events... nothing dramatic but far better than the standard zonal setup.

I hope that's gone at least some way to explaining why I keep going on about the MJO at the moment 

Got to head out again now, will catch up this evening.

Need to keep an eye on this little feature:

Introduces strong winds to the bulk of the country this time, so could be more disruptive.  Also - would be some snow around.  So some really horrible conditions for the Peak district and Snowdonia.

GFSP puts it on a slightly more southerly track:

I am liking the output, plenty of snow to come up here 

Hi all,

Here's today's video update;

Severe Winds And Cooler Late January Hints;

http://www.gavsweathervids.com/

Also has a look at Start warming, the jet stream + More...

The GEFS mean for +300 has high pressure to our SW and low to the NW so nothing has made me change my forecast and it's as you were - unsettled, windy at times, near average temps.
I'm looking forward to the -2c temp at 12noon in Aberdeen on Saturday that Michael made the effort to show me yesterday - at least it will provide a distraction from this zonal dross :)

This morning's ECM control run paints a cold, wintry picture with all areas having seen snow by T+324 - and most of the UK having seen snow well before then.

What's interesting is that it's a mobile pattern throughout, with southerly-tracking lows and plenty of northern-edge snowfall events for more northern areas of the UK. The majority of members in the EPS ensembles continue to show a colder-than-average period from the 17th.

GFSP is like GFS's mad little brother. It always ramps up the lows in a tabloid fashion.

It hopefully looks like the Azores ridge will start to bugger off and we can get a more southerly track for these systems. Not really good enough for snow down here but Midlands northwards might do quite well

I normally ignore the mean in these situations and focus on what is being shown by the individual perturbations. If I were to forecast at T+300 (which I wouldn't) I would base my forecast on the pattern that most members go for rather than a mean.

GFS adjusting toward ECM days 7-8... got to keep an eye on that secondary low as it tracks into the UK rather than bombing out to our NW.

The 06z then produces another mid-Atlantic bomb yet jet disruption still manages to send it sliding southeast with very wintry results. Meanwhile high latitude blocking is slowly but surely on the increase.

GFSP has the sliding low too but as a weaker feature, produces a cold undercut from the east with a rain to snow event. There's then a push of energy to Greenland but this is quickly sent packing SE as well as the pattern remains amplified and again, high latitude blocking begins to take hold.

With this particular pattern being advertised by GFS/GFSP and GEFS, the Azores High remains prominent to the SW of the UK and low pressure is often tracking NW of the UK before the disruption sends it SE.

Variation among the members in the timing of the lows will cause the mean to snow LP to the NW and high pressure to the SW as Neil posted... but look at the angle of the trough and where it is heading:

This shows the sliding motion expected, and with such clarity on the mean output, suggests that the vast majority of runs are showing this second sliding trough. No wonder the op run is similar!

The mean also resembles the op run days 7-10, with the mid-Atlantic ridge behind the first sliding trough being quickly flattened. A good chance based on this that it will turn cold enough for a transitory snow event, after which is breifly turns milder around days 10-12, followed by a steady drop in temperatures.

The GFSP 06z shows how this flattening of the first ridge might take a bit longer than GEFS are suggesting, which would be in line with the usual GEFS bias.

Odds are it does flatten at some point though, at which time it comes down to how quickly jet disruption can cause energy to slide SE. It could even be fast enough to allow a cut-off ridge to persist around Greenland, as the 00z GFSP and ECM op runs suggested. That would leave us in a good position for the next mid-Atlantic ridge.

Finally for now... the MJO and it's impacts is a well established phenomenon in meteorology, used by forecasting centres around the world, not "another untested theory that has taken its fashion on weather forums as of late". 

So don't go dissing it - or I'll start deleting all of your posts 

The GEFS 06h run presents a developing colder situation.

 At 240h(Sun 18th) the split cold:warm ENS is 50:50.By 384 the cold; warm split is 75:25 suggesting increasing chances of cold.

The change at 240h is driven by the LP to the east introducing northerlies plus mid Atlantic ridging with northerlies and a couple of weak Greenland HP's.

At 384h the cold ens are split between GH and Mid Atalatic ridging and  the odd scandi and UK high.

The detailmay change but tentative signs  of a shift in pattern away from the roaring jet.

Okay one more brief comment - it seems like there are some on here (not Retron of course) who associate 'mobility' with lows tracking west to east, when actually it can involve lows tracking S/SE as described above.

These setups tend to be on a knife edge down south and in past experience it ends up the wrong side of marginal quite often, but with at least one occasion where it goes well and some lying snow is seen, though not tending to stick around for more than a day or two.

January 2013 makes is good case study for this, I'm sure most on here can remember how that went - snow for many but severe cold lacking.

I think back then we were looking for a SSW to set up a cold, snowy February, but it didn't shift the patterns in our favour. This time around it seems like the MJO will have a bigger say at first, with a good trend for a more amplified and blocked pattern based on recent output, while any strat. impacts are up in the air, so to speak.

Phew... I'm getting a bit fired up from all the MJO/amplification/disrupted jet explanations! I'm putting together a document that explains them all as clearly as I can manage - should be able to transfer that onto this forum at some point soon, perhaps in the knowledge base somewhere.

Just a quick heads up -  I'll be adding in GEFS postage stamps to the TWO chart viewer shortly. I've embedded scaled down versions of the 850hPa and precipitation plots as examples from this morning's 6z run. The charts will be stepped at 6 hour intervals from t+ 6 to t+384. There'll also be 500hPa and precip type plots.

Good work Brian 

I second that, postage stamps are definitely something I can support, its a tool I use possibly more than any other for 180hr+

Anyway the pattern today isn't so different to yesterday, we aren't seeing a height rise over Greenland that I would like but there is definite cyclosis visible, most notably on the GFS and the ECM. 

All in all I would sum the situation up as, we probably will get a cold spell, and it probably will be more than a flurry on anoch mor but it may require some patience. I see the situation becoming ever more favourable as the month goes on.

One positive from the current synoptics.Because the troughs are whipping through pretty swiftly,and not stalling, we are getting some good sunshine levels between them.

Better than anticyclonic gloom!

Or cyclonic gloom!

I await the next round of charts with some anticipation (not massive amounts just yet)

Key things to watch out for in the 6-10 day range look to be how far south the shortwave low - perhaps two lows based on GFSP - tracks as it reaches the UK in about a week's time, how far it then digs into Europe, and how strong/flat the jet is in the far-western Atlantic days 9-10.

The further south the shortwave(s) track, the more chance of cold undercut(s) providing some at least transitory snow somewhere across England and Wales.

The further they dig into Europe, the more chance of seeing a brief easterly from the toppling mid-Atlantic ridge with a chance of snow if the trough doesn't sink too far south.

The weaker/less flat the jet is west of that ridge, the longer it will take for the Atlantic to return, and the greater the chance of the jet diving south again with residual heights near Greenland (basically a region of relatively warmer air and/or high pressure sticking around N or NW of the UK) forcing the trough to take on a NW-SE orientation which is good for keeping the cold air in play.

There will inevitably be operational runs and ensemble members that don't manage all of this, and it is possible that we will end up with something like the GFS 06z where the Atlantic really powers its way back over to the UK, leaving us waiting for it to slide SE from a starting point right over our heads.

It's hard to say which way GFS and co. are likely to trend, because on one side there's the usual bias toward ramping up the jet (mostly in lower-res, even on GFSP from what I've seen), but on the other there's the likely overcooking of the MJO and hence overdone signal for amplification of the pattern in the 10-16 day range. 

One thing we should not expect to see until week four of this month (i.e. the far end of current GFS/GFSP/GEFS runs) at the earliest is extensive high latitude blocking, because it's only then that the background signals start to indicate that the stage will be set for it's appearance.