Model Output Discussion - Colder but how cold and for how long?

[alexisj9]

45 minutes ago, WYorksWeather said:

Very, very unlikely to be anything like that cold. That specific ensemble was record-breaking at 850hPa but around 10C at the surface, with very low diurnal range, so probably fog and cloud, but definitely not freezing fog! Quite a few ensembles getting into the mid-teens.

This morning, the warmer options are continuing to gain traction. ECM mean is at 5C at 850hPa, GFS not quite that high, but on balance probably starting to move in that direction.

In terms of surface conditions, the ECMs 00z P09 shows surface temperatures peaking at 15C in London on January 23rd at midday. Historically these are underestimates, don't account for afternoon heating since it jumps from 12z to 18z, and of course that is a spot temperature for London which may not be the warmest location, so 17C is quite possible somewhere.

As an example of what this might look like, here's the chart for P9:

Can only get a detailed view for the south using Meteociel's France view, but that's widespread 12C at mid-day from London and the SE up through East Anglia, parts of the Midlands, even into Yorkshire. The darker yellow colour is 14C for the SE and East Anglia. And in practice, usually the ECM under-reads the spot maxima, so add 1-2C is a safe bet for the UK-wide daily maximum.

Of course, this is only one scenario, but even the mean has a maximum of 11C in London, and very widespread double figures (the cream colour):

Still a few days away, but as long as those exceptionally mild options remain in the ensemble, I'd be loathe to dismiss them, since quite often mild gets upgrades and cold gets downgrades.

 

 

 

 

Yep with the iso bars I can see why, the winds mix the air and bring the warmth down.

[minus10]

Well have to say that looking at this fax its a pity not more could be made of this set up for midweek snow in the south..

..three seperate frontal systems to the south !!...yet we will struggle to get a flake....although not if the bbc app for London is to be believed..

??

...return to mild has been well forcasted however very strong signal of this on the 0z eps

..vortex looking strong and robust for last week of February..its amazing how quick it has devoured the Greenland high...

...the anoms show some amplification at the end of the month but as currently shown it wont benefit us for cold..

...indeed could get quite mild for a while..although if the high anom keeps moving north it could then be more favourable for cold...

..so yes disappointing really as was hoping for more...however cold week coming up with some frosts and somewhere in uk will get snow. Got to hope that the favourable drivers kicking in again for late January / February as predicted do promote blocking in the right place for delivering cold and snow to the uk...not an easy task...enjoy what you can...

 

 

[Derecho]

I think now that things are quietening down I thought it'd be interesting to go through some teleconnections for this period... how well did they verify?

The MJO has been amplified recently and has been my main source of focus. Just before Christmas there was a strong indication we would go into phase 7 and phase 8 and from that I suggested things may start getting interesting from January 5th...

So from the diagram below you can see we went into phase 1 on December 23rd. There is a 10-12 day lag with these...

So what follows a Dec phase 1 in an El Nino year? and what did we get 10 days later?

IMO a good match as you can see the troughing over the UK following some ridging over the mid-Atlantic. Next we went into phase 2 around the new year...

This looks quite different, instead we got the cold easterly following on from the troughing in the north Atlantic. Then we went into a phase 3 around January 4th which strangely looped round into phase 2. Looking at both these composites and what actually happened...

The MJO composites appear to be onto something here with an upper trough dropping towards the UK with heights to the NW, however the area of low heights was focused over Scandi instead. Despite the prolonged period in phase 3 we also see the Atlantic coming in early. My thoughts were the Atlantic would start ramping up around the 25th but it looks to be several days early.

Phase 4 we went into yesterday which can be cold if we are on the right side of a battleground but it looks like we won't be.

If the MJO really is a key driver then is the lag time of 10-12 days reliable because it looks like the phase 4 composite sets in after 5-6 days rather then 10...

Into the future now and as you might expect, phase 5 is poor... and phase 6 is very strongly zonal.

 

Applying a 6 day lag rather then 10 the mild pattern will take us up to around February 3rd... then the phase 7 Jan and Feb Nino composites are as follows...

A cross between the two suggests a strong mid-Atlantic ridge or a northerly around the turn of the month. However will the MJO remain amplified at this point? We know what happened in December.

However if we can stick it out to phase 7 and 8 we should see some good blocking.

In the more reliable, still some ensemble members are dropping SLP off the west coast of Spain towards the end of the week. It probably won't stop the Atlantic onslaught next week but it may reduce the window for mild air... and keep the weekend more cold and Anticyclonic as the Atlantic is slower to push in.

[AO-]

Even though the synoptics have potential the EPS does not show anything wintry for my location in FI. Let's hope and pray for wintry showers n monday and snow on Tuesday. Both raw (06) and corrected (00) output added.

Edited January 14 by AO-

[Ali1977]

1 minute ago, minus10 said:

Well have to say that looking at this fax its a pity not more could be made of this set up for midweek snow in the south..

..three seperate frontal systems to the south !!...yet we will struggle to get a flake....although not if the bbc app for London is to be believed..

??

...return to mild has been well forcasted however very strong signal of this on the 0z eps

..vortex looking strong and robust for last week of February..its amazing how quick it has devoured the Greenland high...

...the anoms show some amplification at the end of the month but as currently shown it wont benefit us for cold..

...indeed could get quite mild for a while..although if the high anom keeps moving north it could then be more favourable for cold...

..so yes disappointing really as was hoping for more...however cold week coming up with some frosts and somewhere in uk will get snow. Got to hope that the favourable drivers kicking in again for late January / February as predicted do promote blocking in the right place for delivering cold and snow to the uk...not an easy task...enjoy what you can...

 

 

The last METO didn’t mention it, so I’m hoping that’s because it’s changing all the time. We need a big move north on the 12z - v unlikely but certainly possible!! 

[alexisj9]

3 minutes ago, minus10 said:

Well have to say that looking at this fax its a pity not more could be made of this set up for midweek snow in the south..

..three seperate frontal systems to the south !!...yet we will struggle to get a flake....although not if the bbc app for London is to be believed..

??

...return to mild has been well forcasted however very strong signal of this on the 0z eps

..vortex looking strong and robust for last week of February..its amazing how quick it has devoured the Greenland high...

...the anoms show some amplification at the end of the month but as currently shown it wont benefit us for cold..

...indeed could get quite mild for a while..although if the high anom keeps moving north it could then be more favourable for cold...

..so yes disappointing really as was hoping for more...however cold week coming up with some frosts and somewhere in uk will get snow. Got to hope that the favourable drivers kicking in again for late January / February as predicted do promote blocking in the right place for delivering cold and snow to the uk...not an easy task...enjoy what you can...

 

 

Omg I've missed a whole month somewhere, what happened to the rest of January, and beginning of Feb. Knew I was tired but must have slept a long time.

[CoventryWeather]

The GEFS seems more interested in Wednesdays low being further north than the 00z - about 6/7 show snow as far as the midlands. 

I do wonder if the models will start a small shift north in the next couple of days, instead of the shift south. Overnight modelling has pulled Tuesdays low northwards and is a tad stronger, first seen by the GFS. Keep an eye on the ECM/EPS 06z in the next hour to see whether they pull northwards. Say a middle ground solution seems a tad more likely now, perhaps the south coast getting something.

[tight isobar]

8 minutes ago, Ali1977 said:

The last METO didn’t mention it, so I’m hoping that’s because it’s changing all the time. We need a big move north on the 12z - v unlikely but certainly possible!! 

The 00z London ones say… precipitation “highly likely “ between 16/18th on we roll….  To add gfs 6z snow depth chart for the same time “ given it’s all subjective atm” but rays of light certainly filtering through on this ..

Edited January 14 by tight isobar

[alexisj9]

1 minute ago, CoventryWeather said:

The GEFS seems more interested in Wednesdays low being further north than the 00z - about 6/7 show snow as far as the midlands. 

I do wonder if the models will start a small shift north in the next couple of days, instead of the shift south. Overnight modelling has pulled Tuesdays low northwards and is a tad stronger, first seen by the GFS. Keep an eye on the ECM/EPS 06z in the next hour to see whether they pull northwards. Say a middle ground solution seems a tad more likely now, perhaps the south coast getting something.

I'm just wondering, looking at the position of the front coming down from the north on the fax chart, if what we are seeing is actually that front being a bit stronger on some models, hence snow along it in the south, while it waits for the low further south to clear away.

[Catacol]

54 minutes ago, Scandinavian High. said:

Hello where are we looking at blocking north west or north/north east or is it to early? For that direction. Thank you.

Hmmm - that is a good question. Ultimately it will be to the NW - but there is going to be a transitionary phase that might well feature a block to the NNE first. At the moment - and the reason I have been quiet for a couple of days - is that we have nailed on 5 days of cold and then the arrival of a couple of factors that I have no confidence in the modelling’s ability to manage in any great detail and so I’d rather sit and watch and be fascinated.

In the first place we have a bottom up short term vortex split that is going to end quickly and allow the vortex to reform as a whole once again, but quite how that happens and the extent to which frictional responses to this are going to impact the tropospheric pattern is very unclear.

Secondly we have a solidly Nino-esque atmosphere that is sitting in a positive momentum position even as we reach the end of the inevitable ping back from the steep rise in late December, and that means (as has been stated better by others) that our baseline is already predisposed to blocking. So…when NWP wakes up to the rising momentum picture signalled by my FT screenshot earlier and enhanced soon by an imminent +EAMT and a very favourable MJO we end up with the Glosea Feb chart.

The Hannibal Smith pic from a few posts back holds true still. There is nothing happening that is especially unexpected. I am quietly gutted that we did not get the forecast SSW earlier in January because I think if that had happened we would have been looking at wall to wall cold blocking for the extended, but right now the steering wheel is being grasped by tropospheric forcings that are well expressed in the GSDM…and it is a great watch. Whatever falls from the sky this week will not be winter’s final hurrah.

Going back to your question - I can see NWP playing around with a more downstream wave break setting up over Scandy in the first place, so I’ll plump for a U.K./Scandy ridge first and then retrogression to Greenland. To be honest this is hardly an original view point - EC weeklies have been flagging that progression for a while.

[blizzard81]

3 minutes ago, Catacol said:

Hmmm - that is a good question. Ultimately it will be to the NW - but there is going to be a transitionary phase that might well feature a block to the NNE first. At the moment - and the reason I have been quiet for a couple of days - is that we have nailed on 5 days of cold and then the arrival of a couple of factors that I have no confidence in the modelling’s ability to manage in any great detail and so I’d rather sit and watch and be fascinated.

In the first place we have a bottom up short term vortex split that is going to end quickly and allow the vortex to reform as a whole once again, but quite how that happens and the extent to which frictional responses to this are going to impact the tropospheric pattern is very unclear.

Secondly we have a solidly Nino-esque atmosphere that is sitting in a positive momentum position even as we reach the end of the inevitable ping back from the steep rise in late December, and that means (as has been stated better by others) that our baseline is already predisposed to blocking. So…when NWP wakes up to the rising momentum picture signalled by my FT screenshot earlier and enhanced soon by an imminent +EAMT and a very favourable MJO we end up with the Glosea Feb chart.

The Hannibal Smith pic from a few posts back holds true still. There is nothing happening that is especially unexpected. I am quietly gutted that we did not get the forecast SSW earlier in January because I think if that had happened we would have been looking at wall to wall cold blocking for the extended, but right now the steering wheel is being grasped by tropospheric forcings that are well expressed in the GSDM…and it is a great watch. Whatever falls from the sky this week will not be winter’s final hurrah.

Going back to your question - I can see NWP playing around with a more downstream wave break setting up over Scandy in the first place, so I’ll plump for a U.K./Scandy ridge first and then retrogression to Greenland. To be honest this is hardly an original view point - EC weeklies have been flagging that progression for a while.

Another fab post there. I really enjoy reading your posts. It also looks like the cfs is singing from the same hymn sheet. 

[clark3r]

Gfs has been showing snow in the far south last few runs on Wednesday! I just wonder if the ECM will catch on tonight or tomorrow! Equally it may go the other way the gfs May drop the idea! 
 

 

[Tamara]

3 minutes ago, Derecho said:

I think now that things are quietening down I thought it'd be interesting to go through some teleconnections for this period... how well did they verify?

The MJO has been amplified recently and has been my main source of focus. Just before Christmas there was a strong indication we would go into phase 7 and phase 8 and from that I suggested things may start getting interesting from January 5th...

So from the diagram below you can see we went into phase 1 on December 23rd. There is a 10-12 day lag with these...

So what follows a Dec phase 1 in an El Nino year? and what did we get 10 days later?

IMO a good match as you can see the troughing over the UK following some ridging over the mid-Atlantic. Next we went into phase 2 around the new year...

This looks quite different, instead we got the cold easterly following on from the troughing in the north Atlantic. Then we went into a phase 3 around January 4th which strangely looped round into phase 2. Looking at both these composites and what actually happened...

The MJO composites appear to be onto something here with an upper trough dropping towards the UK with heights to the NW, however the area of low heights was focused over Scandi instead. Despite the prolonged period in phase 3 we also see the Atlantic coming in early. My thoughts were the Atlantic would start ramping up around the 25th but it looks to be several days early.

Phase 4 we went into yesterday which can be cold if we are on the right side of a battleground but it looks like we won't be.

If the MJO really is a key driver then is the lag time of 10-12 days reliable because it looks like the phase 4 composite sets in after 5-6 days rather then 10...

Into the future now and as you might expect, phase 5 is poor... and phase 6 is very strongly zonal.

 

Applying a 6 day lag rather then 10 the mild pattern will take us up to around February 3rd... then the phase 7 Jan and Feb Nino composites are as follows...

A cross between the two suggests a strong mid-Atlantic ridge or a northerly around the turn of the month. However will the MJO remain amplified at this point? We know what happened in December.

However if we can stick it out to phase 7 and 8 we should see some good blocking.

In the more reliable, still some ensemble members are dropping SLP off the west coast of Spain towards the end of the week. It probably won't stop the Atlantic onslaught next week but it may reduce the window for mild air... and keep the weekend more cold and Anticyclonic as the Atlantic is slower to push in.

The discrepancies are accounted for b/c the MJO is only one part of the total global wind-flow budget. As repeated very often on this thread there has to be analysis of the relationship of the tropics with the extra tropics c/o using the diagnostics from the GSDM (Global Synoptic Dynamical Model). Its another fancy sounding acronym, but it provides data that gives a fuller guide to the global atmosphere and associated jet stream as a whole. The MJO composites used in isolation make too many x+y= assumptions about how the extra tropics might behave in a linear fashion to the MJO based on a given ocean base state. The reality is that the fluxing of the atmosphere is more flexible than that and the extra tropical wind-flow can be disconnected from the tropics at a given time based on inertia lags and variations of directional fluxing of MJO eddies into the extra tropics..

 Equatorward fluxing of AAM anomalies within the extra tropics will offset propagating poleward attempts of momentum transport and scramble the MJO composite if used in isolation that doesn't account for the contrary signal within the extra tropics. That is, it doesn't read the disconnect in the extra tropics, it just assumes a typical amplification pathway associated with the base state that the composite was selected upon. On this basis, it is not as simple as MJO propagation through Phases 7,8,1 inevitably = HLB. Each situation has to be taken on its own merits.

Based on readiness for the atmosphere to be conducive to poleward (not equatorward) momentum of MJO +ve AAM anomalies associated with a high amplitude propagation to the Pacific, this is one occasion however where a higher latitude synoptic response is much more likely. As reflected by the Global Wind Oscillation which takes account of the extra tropical wind-flow budget as well as the MJO itself.

Equatorward fluxing on the other hand in stark contrast can produce an inflated sub tropical high response through the same amplified Pacific phases. A good example of this was back in February 2019 - where expectations had widely been for a very strong HLB response (and associated with an SSW).

The converse happened with very mild Springlike weather in the UK.

[steveinsussex]

Weirdly the met office going for sleet and rain to lower levels in the north on Tuesday?!

 

3.40 mark on here

 

 

[MJB]

8 minutes ago, blizzard81 said:

Another fab post there. I really enjoy reading your posts. It also looks like the cfs is singing from the same hymn sheet. 

Ditto, I like Cats posts very informative ,  I like the read 

[bluearmy]

Just now, steveinsussex said:

Weirdly the met office going for sleet and rain to lower levels in the north on Tuesday?!

 

3.40 mark on here

 

 

Warm sector on a wave that doesn’t originate in the frigid flow 

the shortwaves have spoiled this week for most. 

the nwp has counted down pretty well from a couple weeks out - but the ens means won’t see the shortwaves and they can be effective in cutting off the flow 

in tandem with the n American trough being poorly modelled because it’s not going to dig as far south as predicted and sustain for a few days and we see the Atlantic flattened. A deeper n American trough would have sent WAA downstream and helped keep the ridging to our west. And finally the Arctic field remain unpredictable as ever. 

[MJB]

6 minutes ago, steveinsussex said:

Weirdly the met office going for sleet and rain to lower levels in the north on Tuesday?!

 

3.40 mark on here

 

 

Small area of less cold air maybe ????

[Badgers01]

1 minute ago, bluearmy said:

Warm sector on a wave that doesn’t originate in the frigid flow 

the shortwaves have spoiled this week for most. 

the nwp has counted down pretty well from a couple weeks out - but the ens means won’t see the shortwaves and they can be effective in cutting off the flow 

in tandem with the n American trough being poorly modelled because it’s not going to dig as far south as predicted and sustain for a few days and we see the Atlantic flattened. A deeper n American trough would have sent WAA downstream and helped keep the ridging to our west. And finally the Arctic field remain unpredictable as ever. 

Well put nothing weird about it !

[DrJim]

15 minutes ago, clark3r said:

Gfs has been showing snow in the far south last few runs on Wednesday! I just wonder if the ECM will catch on tonight or tomorrow! Equally it may go the other way the gfs May drop the idea! 
 

 

Being in the South, I would take what GFS is showing but I'm having a hard time trusting any of the models +48 with regard precipitation and the track of this low. I'm looking to the higher resolution models nearer the time for the track of the midweek feature. 

[JimBob]

Met office warnings now out until Thursday and none for the south so they see no risk of snow down here. 

Edited January 14 by JimBob

[tight isobar]

Just now, JimBob said:

Met office warning now out until Thursday and none for the south so they see no risk of snow down here. 

These warnings will wax n wane over the nxt few days- as to be expected in such a flow- tiny increments will change possible warning zones/ areas.  Seen this MANY times ..

[steveinsussex]

14 minutes ago, Badgers01 said:

Well put nothing weird about it !

Eh? There has been no mention about rain this week ! If these mild sectors are now popping up then it’s new

[Windysun1]

26 minutes ago, Tamara said:

The discrepancies are accounted for b/c the MJO is only one part of the total global wind-flow budget. As repeated very often on this thread there has to be analysis of the relationship of the tropics with the extra tropics c/o using the diagnostics from the GSDM (Global Synoptic Dynamical Model). Its another fancy sounding acronym, but it provides data that gives a fuller guide to the global atmosphere and associated jet stream as a whole. The MJO composites used in isolation make too many x+y= assumptions about how the extra tropics might behave in a linear fashion to the MJO based on a given ocean base state. The reality is that the fluxing of the atmosphere is more flexible than that and the extra tropical wind-flow can be disconnected from the tropics at a given time based on inertia lags and variations of directional fluxing of MJO eddies into the extra tropics..

 Equatorward fluxing of AAM anomalies within the extra tropics will offset propagating poleward attempts of momentum transport and scramble the MJO composite if used in isolation that doesn't account for the contrary signal within the extra tropics. That is, it doesn't read the disconnect in the extra tropics, it just assumes a typical amplification pathway associated with the base state that the composite was selected upon. On this basis, it is not as simple as MJO propagation through Phases 7,8,1 inevitably = HLB. Each situation has to be taken on its own merits.

Based on readiness for the atmosphere to be conducive to poleward (not equatorward) momentum of MJO +ve AAM anomalies associated with a high amplitude propagation to the Pacific, this is one occasion however where a higher latitude synoptic response is much more likely. As reflected by the Global Wind Oscillation which takes account of the extra tropical wind-flow budget as well as the MJO itself.

Equatorward fluxing on the other hand in stark contrast can produce an inflated sub tropical high response through the same amplified Pacific phases. A good example of this was back in February 2019 - where expectations had widely been for a very strong HLB response (and associated with an SSW).

The converse happened with very mild Springlike weather in the UK.

So basically you cannot forecast with any great accuracy with these signals as there are too many variables?

[IanT]

In the investment world we recognise what is called the “pain trade”. It’s the outcome least expected/favoured by the majority of forecasters; the outcome that few forecasters expect or want and that even fewer are positioned for. It’s pretty clear that the pain trade here - for both the NWP models and NW’s forecasting community - would be for the SE (& London in particular) to get buried later this week. The “French low” tracking N to deliver a headline dominating Cobra-level snow event in the most heavily populated portion of the country…

Pain trade outcomes occur more frequently than expected, because outcomes in the tails of distribution approximations are - by definition! - unusual and hard to forecast. That’s why experienced/canny forecasters like the MetO take great care to allow some space for tail outcomes in their forecasting language. I think we can see that in action here…

[Gadje]

2 hours ago, MJB said:

Beeb forecast have lowest temps around 2 c by day ( south ) but mentioned sharp overnight frosts.

Windchill from this tomorrow in the South -2

More widespread snow in Central Southern Scotland on Tuesday. No mention or chart shown for the LP in the Channel, tells me it's insignificant. Mild and wet next weekend.

Standard winter week I'd say.

 

 

'Widespread snow in Central Southern Scotland' isnt a 'standard winter week' in January believe me.