Model output discussion 9th April onwards

[stodge]

Evening all

As we discussed last evening, the progress of next weekend's LP far from resolved. GFS pushed it through quickly from west to east but others are toying with slowing the system down to the west and obviously, were that to happen, we'd see much warmer air advected north over (primarily) southern and eastern Britain.

The T+168 charts from ECM, GEM, JMA, GFS OP and GFS Control from the 12Z runs.

So we're basically looking at three options:

1) ECM - the LP stalls briefly to the west and then slides SE into Europe - the T+240 has renewed northern blocking and an ENE'ly flow so any warmth is going to be short lived.

2) GEM/JMA - these take the LP further north so it's a more conventional SW or W'ly flow as the LP approaches but the two diverge sharply after that. GEM basically fills the LP in situ while JMA ends on a warm note with heights to the east (possibly the pick of the models tonight for warm fans)

3) GFS - both OP and Control take the LP through and across the British Isles quickly. The result is we get a chilly and possibly quite potent N'ly.

At this stage, all options on the table.

[minus10]

4 minutes ago, stodge said:

Evening all

As we discussed last evening, the progress of next weekend's LP far from resolved. GFS pushed it through quickly from west to east but others are toying with slowing the system down to the west and obviously, were that to happen, we'd see much warmer air advected north over (primarily) southern and eastern Britain.

The T+168 charts from ECM, GEM, JMA, GFS OP and GFS Control from the 12Z runs.

So we're basically looking at three options:

1) ECM - the LP stalls briefly to the west and then slides SE into Europe - the T+240 has renewed northern blocking and an ENE'ly flow so any warmth is going to be short lived.

2) GEM/JMA - these take the LP further north so it's a more conventional SW or W'ly flow as the LP approaches but the two diverge sharply after that. GEM basically fills the LP in situ while JMA ends on a warm note with heights to the east (possibly the pick of the models tonight for warm fans)

3) GFS - both OP and Control take the LP through and across the British Isles quickly. The result is we get a chilly and possibly quite potent N'ly.

At this stage, all options on the table.

As you say all options on the table. Another interesting period of model watching coming up and at least something to talk about different to the cold northerlies. Although the ECM at 240 has a renewed HP to the north it looks to me that the warm air is fairly well established by then over Europe Stodge and would be coming our way in the east/north east wind. Therefore day 6 to day 10 is warmer and could it not last a bit longer? Misty and cloudy perhaps on the eastern side still owing to cool North Sea but warm in any sunny breaks. All conjecture I suppose at this timescale but at least it is encouraging to see these charts now being shown.... 

[Scorcher]

3 minutes ago, minus10 said:

As you say all options on the table. Another interesting period of model watching coming up and at least something to talk about different to the cold northerlies. Although the ECM at 240 has a renewed HP to the north it looks to me that the warm air is fairly well established by then over Europe Stodge and would be coming our way in the east/north east wind. Therefore day 6 to day 10 is warmer and could it not last a bit longer? Misty and cloudy perhaps on the eastern side still owing to cool North Sea but warm in any sunny breaks. All conjecture I suppose at this timescale but at least it is encouraging to see these charts now being shown.... 

I agree, heights to the north doesn't guarantee warmth won't last. In fact the ECM shows a potential scenario where it actually clings on in spite of this.

We've seen this before when a trough stalls to the west of France and keeps a continental flow going. It doesn't matter too much about northern blocking in that scenario.

All conjecture at this point though. It is a feasible evolution though from the ECM. Could be a remarkable turnaround if this comes off.

[phil nw.]

After so many weeks of cold north/north easterly flows some tentative signs from ecm at t144 that we may see some warmer air from further south.

Not yet settled though with rain set to move in from the Atlantic but the higher temps along with the rainfall should speed up Spring growth after being held back somewhat. 

Edited May 2, 2021 by phil nw.

[stodge]

7 minutes ago, minus10 said:

As you say all options on the table. Another interesting period of model watching coming up and at least something to talk about different to the cold northerlies. Although the ECM at 240 has a renewed HP to the north it looks to me that the warm air is fairly well established by then over Europe Stodge and would be coming our way in the east/north east wind. Therefore day 6 to day 10 is warmer and could it not last a bit longer? Misty and cloudy perhaps on the eastern side still owing to cool North Sea but warm in any sunny breaks. All conjecture I suppose at this timescale but at least it is encouraging to see these charts now being shown.... 

Absolutely. This would be a "summer" easterly with the air from a much warmer source. You are also quite correct to point out the warmer air passing over the colder sea is going to make it misty with haar or fret for eastern coastal counties making it cool but inland it would be warm and very pleasant with +8 850s and with a slack trough over us plenty of opportunity for some hefty showers.

[Mike Poole]

ECM 12z ensembles mean at T240, euro and NH:

I know we are looking at 10+ days for summer weather, but this is a start - once there is nose from the Azores it is not clear where the resistance comes from?  

Spread, T240:

Hint : jet stream is going north of us by this point!  Start of summer = 17 May, but didn’t we know that anyway!

[Frosty.]

I know what you’re all thinking?..yeah I’m a mind reader  in my spare time! ..and the answer is YES!...there is some support for the warm / tropical air being scooped up that the ECM 12z op shows!..I need to go have a lie down now....I’ve even shown a few charts twice.. ..far too much excitement for a Sunday evening!  

Edited May 2, 2021 by Jon Snow

[Mike Poole]

ECM clusters T192-T240:

1-4 have some kind of block that might flood certain parts of the country with southerly winds for a while at the earlier timeframe.  Later T264+

1-3 potential for the start of summer maybe, by T360 anyway, a small signal but it should grow I think as AAM rebounds:

Caveat needed, AAM plots are from the same models that are fallible beyond 4 days.  This is why I’m not as sure as some that AAM is the best predictor of future evolution.  It seems to me it is predictable by models that might quite as well be wrong.  The only AAM prediction i get to see is the CFS and we know how that compares to chocolate teapots.  I persist with looking at, and learning about, AAM because I do believe it has some predictive capability but it can be overstated.   I prefer to look at it in the line with seasonal modelling, but giving the seasonal modelling the majority weight in forming my opinions, and conclude from both that a major warm up in mid-May is due, and that it won’t be a direct high pressure hit, so that means some hot humid weather with thunderstorms to come in to summer proper.  

We will see…

 

 

Edited May 2, 2021 by Mike Poole

[Tamara]

42 minutes ago, Mike Poole said:

ECM clusters T192-T240:

1-4 have some kind of block that might flood certain parts of the country with southerly winds for a while at the earlier timeframe.  Later T264+

1-3 potential for the start of summer maybe, by T360 anyway, a small signal but it should grow I think as AAM rebounds:

Caveat needed, AAM plots are from the same models that are fallible beyond 4 days.  This is why I’m not as sure as some that AAM is the best predictor of future evolution.  It seems to me it is predictable by models that might quite as well be wrong.  The only AAM prediction i get to see is the CFS and we know how that compares to chocolate teapots.  I persist with looking at, and learning about, AAM because I do believe it has some predictive capability but it can be overstated.   I prefer to look at it in the line with seasonal modelling, but giving the seasonal modelling the majority weight in forming my opinions, and conclude from both that a major warm up in mid-May is due, and that it won’t be a direct high pressure hit, so that means some hot humid weather with thunderstorms to come in to summer proper.  

We will see…

 

 

There is a simple answer to that, which is not intended at all to be a clever offering It is simply that a numerical model interpretation of AAM  (atmospheric angular momentum is a representation of the turning force of the jet stream) evolves and changes with time and is prone to bias errors over increasing time scales. It is a forecast interpretation, that evolves and changes according to those biases - but it is not the raw diagnostic.

The diagnostic model leads the numerical model, not the other way around. That is why the Global Synoptic Dynamical Model plots exist (GSDM) . They are totally  independent and separate from numerical model forecasts of AAM that are the derived and sometimes flawed interpretations. The numerical AAM forecasts simply provide insight as the how these models interpret jet stream patterns at a given snapshot of time.

A diagnostic model is divorced from model biases - it is a raw consolidated real time calculation of global wind-flow inertia (i.e the changes of the path and velocity of the jet stream) and intended to be used independently of NWP forecasts as an insight as to how numerical models may evolve (and change according to their biases and misreading of signals).

A constant repetition with no apology - signals lead models, models do not lead signals...

As things stand, and according to analysis given earlier this weekend, the first hints are coming that both the atmospheric circulation pattern and changes in seasonal wavelength patterns are starting to adjust the amplification wavelength across both the Pacific and Atlantic. Some retrogression of the pattern is actually a very good thing at the moment for many part of Western and central europe (including also many western Mediterranean regions) because it starts to allow sub tropical heat to finally advect northwards and repel the incessant polar cold air advection that has dominated for so long.

For NW parts of europe and especially the UK on the maritime edges, this is not likely to be seamless warm up. So wise to not see any step change warming up from such a low base as a linear process to sustained warmth but as a staged transition.

However,  assuming that the direction of travel of both tropical and extra tropical forcing remains buoyant as discussed in detail the other day, and adheres to a non dynamic ushering in of the polar stratospheric summer - then there is a way out of the anomalously cold pattern for Northern Europe and which would also represent the first experience of sustained seasonal heat for someone like me who has not embarked on a holiday, but is permanently relocated in her new home - and will need to adjust a way of life to some lovely siesta time 

[offerman]

6 hours ago, Tamara said:

There is a simple answer to that, which is not intended at all to be a clever offering It is simply that a numerical model interpretation of AAM  (atmospheric angular momentum is a representation of the turning force of the jet stream) evolves and changes with time and is prone to bias errors over increasing time scales. It is a forecast interpretation, that evolves and changes according to those biases - but it is not the raw diagnostic.

The diagnostic model leads the numerical model, not the other way around. That is why the Global Synoptic Dynamical Model plots exist (GSDM) . They are totally  independent and separate from numerical model forecasts of AAM that are the derived and sometimes flawed interpretations. The numerical AAM forecasts simply provide insight as the how these models interpret jet stream patterns at a given snapshot of time.

A diagnostic model is divorced from model biases - it is a raw consolidated real time calculation of global wind-flow inertia (i.e the changes of the path and velocity of the jet stream) and intended to be used independently of NWP forecasts as an insight as to how numerical models may evolve (and change according to their biases and misreading of signals).

A constant repetition with no apology - signals lead models, models do not lead signals...

As things stand, and according to analysis given earlier this weekend, the first hints are coming that both the atmospheric circulation pattern and changes in seasonal wavelength patterns are starting to adjust the amplification wavelength across both the Pacific and Atlantic. Some retrogression of the pattern is actually a very good thing at the moment for many part of Western and central europe (including also many western Mediterranean regions) because it starts to allow sub tropical heat to finally advect northwards and repel the incessant polar cold air advection that has dominated for so long.

For NW parts of europe and especially the UK on the maritime edges, this is not likely to be seamless warm up. So wise to not see any step change warming up from such a low base as a linear process to sustained warmth but as a staged transition.

However,  assuming that the direction of travel of both tropical and extra tropical forcing remains buoyant as discussed in detail the other day, and adheres to a non dynamic ushering in of the polar stratospheric summer - then there is a way out of the anomalously cold pattern for Northern Europe and which would also represent the first experience of sustained seasonal heat for someone like me who has not embarked on a holiday, but is permanently relocated in her new home - and will need to adjust a way of life to some lovely siesta time 

Hi Tamara,

 What in your opinion has caused this extremely long cold period of weather to last so long ? 
Why now and not in winter?

 In the sun feels  very pleasant when out of the wind. 
 

Many Thanks and enjoy your new home. 

[Guest]

Is it me or has the GFS since it’s most recent upgrade been far more consistent? Apart from the occasional flip/outlier it just keeps on banging out the same output most of the time well out into FI. Off course it doesn’t mean it’s right but with that consistency it’s really hard to ignore. 

GFS handles the pattern later this week exactly the again this morning, low pressure sliding through the south on Thursday followed by another low through Saturday which then results in colder air again digging in behind into early next week for a couple of days. After then GFS seems to be hinting high pressure building in, maybe some hope towards the end of next week? 

Let’s see what ECM says!!

[Methuselah]

Dearie me, today's GFS 00Z temperature ensembles are nae a pretty sight:

      

[mushymanrob]

18 hours ago, General Cluster said:

IMO, it's at times like these when JH's and mushy's anomaly charts really come into their own? Making predictions based on single model-runs is futile:

GFS 06Z temperature profiles:         

 

Well put it like this, the NOAA charts do not (imho) support the current GFS version of exiting next weekends low rapidly Northeastwards and returning us to colder northerlies.  IMHO they are closer to the ECM, so personally id suggest the current ECM charts are more likely to be closer to the solution than the GFS. But its a game of odds, the GFS has sometimes "beaten" the Anomalies and ECM when they disagree. But more often than not the ECM and Anomalies when broadly agree like they do now, will be nearer the eventual outcome.

[Guest]

Well ECM holding firm along with UKMO suggesting the stalling low is probably the more likely solution, hopefully we don't end up in what I think is the middle group like the GEM continues to show with the low just stalling over the UK for 5-6days....

Before then both ECM and GFS firming up on an extremely cold day and miserable day on Thursday max temps may struggle to get above 6-8C in a large part of the south. 

 

 

[LetItSnow!]

interesting scenario for around the 11th/12th on the GFS 00z - very deep area of low pressure develops over Spain & France with a very sharp temperature gradient at 850hpa. the day before this, it shows only a couple of hundred miles difference from below 0degC to 10-12+degC, thereby fuelling the low pressure and probably giving copious amounts of heavy rain with a NE gale, then -5degC uppers return to Scotland/N England. would feel very 19th century that would!

[Scorcher]

Seems the BBC are going with the ECM/UKMO scenario this morning rather than the GFS- they are forecasting a substantial warm up over the weekend (high teens across most of England to low 20s in the south east). It's unlikely to be dry and sunny for most of us but the much warmer air will at least be good for the gardens.

Before then though, it really is remarkable to see the persistence of the -5C 850hPa air over the south of the UK into Thursday. We're almost into the 2nd week of May by that point! I'm not sure we could possibly have been more unlucky with this arctic air.

I'm surprised there is any cold left in the Arctic to be honest- it seems to have been spilling its contents our way for weeks now and not letting up!

When you look at the situation across the Northern Hemisphere, many areas north of the Arctic Circle are considerably warmer than we are at the moment.

 

 

[Penrith Snow]

Very cool week ahead, most of the UK lies within the 528dam line until at least Saturday so expect plenty of showers some wintry with snow on higher hills. The Scottish ski resorts are going to look like St Moritz by Sunday.

[damianslaw]

46 minutes ago, Scorcher said:

Seems the BBC are going with the ECM/UKMO scenario this morning rather than the GFS- they are forecasting a substantial warm up over the weekend (high teens across most of England to low 20s in the south east). It's unlikely to be dry and sunny for most of us but the much warmer air will at least be good for the gardens.

Before then though, it really is remarkable to see the persistence of the -5C 850hPa air over the south of the UK into Thursday. We're almost into the 2nd week of May by that point! I'm not sure we could possibly have been more unlucky with this arctic air.

I'm surprised there is any cold left in the Arctic to be honest- it seems to have been spilling its contents our way for weeks now and not letting up!

When you look at the situation across the Northern Hemisphere, many areas north of the Arctic Circle are considerably warmer than we are at the moment.

 

 

I'm not too surprised, the cold air bottled up over the arctic through second half of Feb and all of March, we were spared its effects - April typically then sees the atlantic shut down and northerlies often surface, I was expecting deep rooted cold should a northerly develop, and the signal that this would be the case this year came on Easter Monday... 

Back to the models, a cold week ahead, quite poor indeed for early May, more frost at night, wintry showers on higher ground may be even some snow to modest levels.. by the weekend signs we may pull in temporarily a warmer continental feed to southern and eastern parts at least ahead of a deepening low pressure system anchored to our SW, conversely the warm air will add injection to rainfall amounts which look significant. Northern parts will remain locked on the cold side of the polar front jet, and quite quickly the warm uppers will be usurped by colder uppers as the system moves into the N Sea and its then back to the theme of the last 5-6 weeks, northerly flow again...

[Scorcher]

36 minutes ago, damianslaw said:

and quite quickly the warm uppers will be usurped by colder uppers as the system moves into the N Sea and its then back to the theme of the last 5-6 weeks, northerly flow again...

I agree with most of your post but not this part- this is by no means certain and I actually think a major pattern change is favoured after the weekend.

If you are just looking at the GFS then yes perhaps. However the Euros and the anomalies are not supporting that scenario.

[Jordan S]

The Arome on the rainfall in the south this afternoon..

A squally back edge of the rain this evening.

Showers behind this tonight some of them heavy and potentially accompanied by strong winds.

For tomorrow a distinct line of heavy showers developing and will be slow moving across central areas.. falling as snow on high ground of northern England and north Wales later.

Wednesday similar, snow potentially in the showers in northern areas again mostly on high ground but possibly to lower levels in places..

Looking back to the low I mentioned in my previous update for midweek so for thursday and the models differing on the track and to a lesser extent intensity of this, some models bringing it north into more central parts England and Wales and others moving it south of us into France. Rather tricky for them to get the detail correct, But nevertheless most likely outcome is low pressure moving through southern areas of England on thursday morning bringing rain for the south some of it possibly heavy. Temperatures very unusually low for May maximum temperatures of 5-7c in the wet weather in the south.

Also depending on the exact development of this low, there is a small chance of some of the rain falling as snow on high ground in a few places on the northern part of this, a more northerly track (which is a possibility) taking precipitation upto central parts of Wales and the Midlands being where the greatest chance of snow on high ground would be.

Arpege..

Likely scenario.

Icon..

unlikely scenario with the low over France..

Not much change for later this week, low pressure developing quickly another very wet and windy spell on saturday for some especially the south and west of the uk, another spell of snow likely for mostly high ground of Scotland too which may be persistent and heavy, much warmer upper air temperatures (particularly compared with the next few days) moving into the south and east of England..

like others have said the Ecmwf probably closest to the mark this weekend and early next week..

Into early next week probably wettest in the south, though don't take this chart below literally.

Likely remaining quite cold in the north next week but probably not as cold as this week.. perhaps a renewed mobile pattern developing later next week with high pressure to the southwest moving closer and drier weather but still wet at times in the south, but wetter in the north with a mainly westerly flow for the uk.. Though could be the case that low pressure systems move over the whole of the uk keeping all areas very unsettled. 

Edited May 3, 2021 by jordan smith

[Methuselah]

Hey folks, its' the GFS's chart for Day 10: promises so much but delivers so little:

     

Edited May 3, 2021 by Polar Maritime
To move discussion on..

[Guest]

Again the GFS Ops run from the 06Z suite barrels the weekend low straight through, zero warm up. 

Then, what the actual hell is this pile of garbage........

 

 

Ever had the feeling of being left out in the cold? If not you will looking at the below chart, in fact GFS doesn't lift temps above 9 or 10C in parts of the south for 4 straight days next week..... This is actually getting beyond a joke now.

 

[MP-R]

1 hour ago, Scorcher said:

I agree with most of your post but not this part- this is by no means certain and I actually think a major pattern change is favoured after the weekend.

If you are just looking at the GFS then yes perhaps. However the Euros and the anomalies are not supporting that scenario.

Indeed. The synoptics throughout April were highly unusual, especially the longevity, so with a bit of oomph in the Atlantic compared to last month, I can't see similar synoptics continuing unabated throughout May - possibly a tussle between colder northerly influence and warmer southerly. All in all, a wet first half of May for many!

[minus10]

3 hours ago, jordan smith said:

The Arome on the rainfall in the south this afternoon..

A squally back edge of the rain this evening.

Showers behind this tonight some of them heavy and potentially accompanied by strong winds.

For tomorrow a distinct line of heavy showers developing and will be slow moving across central areas.. falling as snow on high ground of northern England and north Wales later.

Wednesday similar, snow potentially in the showers in northern areas again mostly on high ground but possibly to lower levels in places..

Looking back to the low I mentioned in my previous update for midweek so for thursday and the models differing on the track and to a lesser extent intensity of this, some models bringing it north into more central parts England and Wales and others moving it south of us into France. Rather tricky for them to get the detail correct, But nevertheless most likely outcome is low pressure moving through southern areas of England on thursday morning bringing rain for the south some of it possibly heavy. Temperatures very unusually low for May maximum temperatures of 5-7c in the wet weather in the south.

Also depending on the exact development of this low, there is a small chance of some of the rain falling as snow on high ground in a few places on the northern part of this, a more northerly track (which is a possibility) taking precipitation upto central parts of Wales and the Midlands being where the greatest chance of snow on high ground would be.

Arpege..

Likely scenario.

Icon..

unlikely scenario with the low over France..

Not much change for later this week, low pressure developing quickly another very wet and windy spell on saturday for some especially the south and west of the uk, another spell of snow likely for mostly high ground of Scotland too which may be persistent and heavy, much warmer upper air temperatures (particularly compared with the next few days) moving into the south and east of England..

like others have said the Ecmwf probably closest to the mark this weekend and early next week..

Into early next week probably wettest in the south, though don't take this chart below literally.

Likely remaining quite cold in the north next week but probably not as cold as this week.. perhaps a renewed mobile pattern developing later next week with high pressure to the southwest moving closer and drier weather but still wet at times in the south, but wetter in the north with a mainly westerly flow for the uk.. Though could be the case that low pressure systems move over the whole of the uk keeping all areas very unsettled. 

Great post again Jordan...what it shows it we are in for much more 'weather' than we have been used to for a while. Also a fair amount of rain is being signalled over next few weeks which, for me, is good , however would also want some warm sunnier periods. No rain yet here today although much of the country is now wet. Also wind is very prominent which is not so good particularly with plants and trees coming into leaf ....

If this LP was to verify aided by the temp difference according to 6z gfs it would be pretty grotty for us on the northern side . Still hoping that ECM is nearer the mark for a warm up after this (hopefully) last week of cold. The old saying "n'er cast a clout till May is out" comes to mind. Still very apt it seems...

Edited May 3, 2021 by minus10

[Polar Maritime]

A few posts hidden and edited, As per forum rules, Please absolutely nothing political in here. Thanks all