Model Output Discussion - 15th March onwards

[damianslaw]

In the short term, an unsettled end to March, capping off what will go down as a very changeable mostly wet and dull March. All models showing quite an interesting evolution synoptic wise, trough disruption come Friday with heights building to the north. As we enter April signal for something more settled but still not especially so, UKMO pulls in a continental feed and the ECM, not from a warm source, indeed northern climes, GFS has flipped around with this scenario but also goes there eventually.

Such synoptics very common place in April and May, the time of year the atlantic traditionally doesn't get its way and we look to the north and east for our weather.

[Cambrian]

It’s interesting how today’s ECM weather regimes probabilities extended forecast sits with the 12z ECM ensemble mean charts at day 10, the 6th April, the day before Good Friday. 

1. ATR signal very weak - as expected, with the continuing presence of the Atlantic low.

2. NAO- and NAO+ signals both weak - understandable, as the pressure over Iceland and the Azores is very similar, both at around 1020 mb with an easterly flow to the north from Scandinavia to Canada, and a westerly flow to the south extending from eastern Canada to Western Europe, and us. The meat in the middle is one long, squeezed, cyclonic sausage, which happens to be at our latitude of 50 to 60 degrees north, poking out the tongue of a trough eastward in our direction.

3. Strong signal for blocking - here is the confounder, there is no proper block over Europe, except for some modest heights over Scandinavia. Besides that, the heights over Europe are neutral. It is being outputted as a block probably in large part only due to the mean pressure over the centre of the Atlantic being 5-10mb lower than Central Europe, the UK and Ireland. 

  

The setup is pretty much a west-based NAO, but happening perhaps a bit further north than where we sometimes see them operating in the winter, and shows how in the UK and Ireland, we can see modelled an Atlantic / Europe zone characterised as being primarily blocked, along with a negligible NAO+ signal, and still see models that hold out the possibility of us experiencing a westerly flow and weather off the Atlantic 

- and so looking towards the ultimate “balance of power” in the Easter models, what appears on the face of it to be a controlling majority block (but is in reality a “faux bloc”) may end up operating much more like a regime increasingly characterised by no overall control, and with a subsequent trend to running even more that way after Easter. 

[damianslaw]

15 minutes ago, Cambrian said:

It’s interesting how today’s ECM weather regimes probabilities extended forecast sits with the 12z ECM ensemble mean charts at day 10, the 6th April, the day before Good Friday. 

1. ATR signal very weak - as expected, with the continuing presence of the Atlantic low.

2. NAO- and NAO+ signals both weak - understandable, as the pressure over Iceland and the Azores is very similar, both at around 1020 mb with an easterly flow to the north from Scandinavia to Canada, and a westerly flow to the south extending from eastern Canada to Western Europe, and us. The meat in the middle is one long, squeezed, cyclonic sausage, which happens to be at our latitude of 50 to 60 degrees north, poking out the tongue of a trough eastward in our direction.

3. Strong signal for blocking - here is the confounder, there is no proper block over Europe, except for some modest heights over Scandinavia. Besides that, the heights over Europe are neutral. It is being outputted as a block probably in large part only due to the mean pressure over the centre of the Atlantic being 5-10mb lower than Central Europe, the UK and Ireland. 

  

The setup is pretty much a west-based NAO, but happening perhaps a bit further north than where we sometimes see them operating in the winter, and shows how in the UK and Ireland, we can see modelled an Atlantic / Europe zone characterised as being primarily blocked, along with a negligible NAO+ signal, and still see models that hold out the possibility of us experiencing a westerly flow and weather off the Atlantic 

- and so looking towards the ultimate “balance of power” in the Easter models, what appears on the face of it to be a controlling majority block (but is in reality a “faux bloc”) may end up operating much more like a regime increasingly characterised by no overall control, and with a subsequent trend to running even more that way after Easter. 

All suggests a very sluggish pattern, what weather we have coming up we could have for quite some time, with the trough edging east but blocked in on itself - a boxed in trough over the UK, never a good synoptic really. No surprise to see the models show trough disruption later this week.

Edited March 27, 2023 by damianslaw

[Rain All Night]

10 hours ago, RainAllNight said:

The ECM and GFS 0z ensemble means are both quite similar and quite interesting this morning, the grabs below are from days 0, 5, 8, 13 and 15. Not quite sure what's happening over the UK and Europe between days 8 and 13...

EDIT: Just noticed that one of the few significant differences between the two ensembles is that the GFS seems to show a surface easterly over the UK on the day 13 chart where as the ECM does not.

The moving average precipitation anomaly charts from both models lose any positive precipitation anomaly over Great Britain by the period 1-7 April, and this remains the case by 4-11 April (which is as far as these runs go):

Wind roses and temps for my back yard on the south coast:

The afternoon ECM ensemble keeps all of the interesting signals from this morning, including the raised heights over the UK around Easter, and seems more confident to indicate that the Atlantic will not break through the "meridian wall" next week:

→→→

No real contradiction coming from the GFS or GEM ensembles either.

Elsewhere, the MJO stays dead. Does this thing still have an influence on proceedings outside of winter?

Edited March 27, 2023 by RainAllNight

[Nick2373]

 

At last the trend switches on the 18z something more seasonal it will feel quite pleasant in the sunshine if cloud cover don't persist, this looks evident towards the 07th with a uptick in temps.  

Good bye winter nothingness hello spring sunshine. 

[RJBingham]

48 minutes ago, Nick2373 said:

 

At last the trend switches on the 18z something more seasonal it will feel quite pleasant in the sunshine if cloud cover don't persist, this looks evident towards the 07th with a uptick in temps.  

Good bye winter nothingness hello spring sunshine. 

That would make for a happy easter.

[Eagle Eye]

On 20/03/2023 at 15:13, Eagle Eye said:

 

setting in a more semi-zonal kind of setup with a jet retraction rather than an equstorward jet as AAM falls from the recent -VE EAMT the retraction is unlikely to be large. The US ridge isn't entirely stable in terms of advection given that it's the start of US storm season it can easily be pulled up via WAA from troughs and that mfavour a weak high possibly sometime around April. AAM is unlikely to rise enough for it now and the North Pacific Jet stays slightly retracted but I think eventually we'll see a poleward shift/extension and as we go into Spring that may favour AWB that leads to a UK-Scandi type high. Given the nuetral/Nino ENSO state expected and how the AAM has been acting over Winter, there may be a slight favour towards a warmer summer however thers only if the high is forced correctly. As it could quite easily be forced into the mid-Atlantic if the SE US ridge remains in place as that's the typical response given that setup as a Rossby packet 'pushes through'. Alternatively, if the forcing from the background signal is for AWB similar to early March then unlikely early March; the high might be pushed more towards a UK-Scandi high and that's typically a warm summer flow as far as I know. It's what some of the seasonal models are showing with an Ekman pumping esque WAA scenario which is really not good for the heat haters.

There's a lot less teleconnection forecasting that can be done for Spring and Summer though and you rely a lot on essentially composites based off how the monsoon seasons go around the world surprisingly. I think it's too early to base Summer of the SSW though as its destructive influence is likely to end sometime in April as the WWB in the ENSO seeks to have had more of an effect on the setup particularly in North America over the recent week or so. So despite SSW's typically having really bad Springs for people who like moderately warm Springs, this might not be too bad. Though I do still worry about the SE US ridge because if it can't get too high then we may have a windier Spring than Winter and if it can't get too low then we may be chillier because it promotes mid-Atlantic blocking and polar maritime air as a side effect. It has to be just right if it remains there.

 

April does look to start off with a UK-Scandi high occurring through CWB but this looks to be the final overriding effects of the SSW in early April that only really show themselves at the surface where the effects of drag are magnified. E'ly forcing from the slightly more disruptive zonal signal (at this time of year) compared to ENSO base state promoting a cold-undercutting start to Spring. I wouldn’t be surprised though if the UK-Scandi high can keep over the UK and the cold flow is aimed more towards Europe but I think for now Spring warmth that lasts longer than a few days will have to be on hold till mid April. Don't see too much stopping it after this CWB event though. That's if it even manages to get a cold flow to the UK or whether the cold undercuts to Continental Europe.

[ANYWEATHER]

3 hours ago, Nick2373 said:

 

At last the trend switches on the 18z something more seasonal it will feel quite pleasant in the sunshine if cloud cover don't persist, this looks evident towards the 07th with a uptick in temps.  

Good bye winter nothingness hello spring sunshine. 

And the 00z ....

[Rain All Night]

42 minutes ago, Eagle Eye said:

April does look to start off with a UK-Scandi high occurring through CWB but this looks to be the final overriding effects of the SSW in early April that only really show themselves at the surface where the effects of drag are magnified. E'ly forcing from the slightly more disruptive zonal signal (at this time of year) compared to ENSO base state promoting a cold-undercutting start to Spring. I wouldn’t be surprised though if the UK-Scandi high can keep over the UK and the cold flow is aimed more towards Europe but I think for now Spring warmth that lasts longer than a few days will have to be on hold till mid April. Don't see too much stopping it after this CWB event though. That's if it even manages to get a cold flow to the UK or whether the cold undercuts to Continental Europe.

What's a CWB?

[Rain All Night]

A spectrum of progressions this morning...

Would love if someone smarter than me could give their thoughts on how robust these look against further Atlantic incursion...

Edited March 28, 2023 by RainAllNight

[Maz]

15 minutes ago, RainAllNight said:

What's a CWB?

I've no idea what it is.

Maybe it should be "Cold Wet Block".  When blocking is evident but all it does is trap a trough in one place giving days of miserable weather.  That's a pattern the UK is good at!!

[Eagle Eye]

50 minutes ago, RainAllNight said:

What's a CWB?

Cyclonic Wavebreaking.

Edited March 28, 2023 by Eagle Eye

[Nick2373]

1 hour ago, ANYWEATHER said:

And the 00z ....

There are more P's on the mild side possilbe  switch back later,  the ppn spikes are dropping if the sky's are clear given the suns strength it will feel warm. 

[ANYWEATHER]

12 minutes ago, Nick2373 said:

There are more P's on the mild side possilbe  switch back later,  the ppn spikes are dropping if the sky's are clear given the suns strength it will feel warm. 

Although we do have to factor there is a high level of Shannon entropy,  so as far as I'm concerned rainfall predictions are pretty useless with this situation. 

[Mike Poole]

1 hour ago, RainAllNight said:

A spectrum of progressions this morning...

Would love if someone smarter than me could give their thoughts on how robust these look against further Atlantic incursion...

Yes, there does look to be a signal in around a weeks time for a ridge to develop in our vicinity, possibly ridging to scandi, which might well settle things down.  Not a straight forward setup with that cut off low near the Azores on some models.  As of this timescale, the strat is still having an influence, I think, and so any high pressure over the UK is likely to be fleeting and may migrate further north, so any warmth might be short lived.  

Beyond this point, the ECM clusters have 6 options T192-T240:

But none of them are +NAO, so I’m not seeing much in the way of atlantic driven weather, however, blocking to the northwest or northeast or both is prevalent.  T264+:

A cold outlook on cluster 1, maybe some spring warmth from cluster 3.  The end of the strat influence is still in sight towards the end of the GFS run:

So whether that will mean some warmth or some wet will probably depend on how far north the jet stream pushes at this time, as the likelihood of high latitude blocking diminishes.

Edited March 28, 2023 by Mike Poole

[Rain All Night]

Days 7, 10.5 and 14 on the three 0z ensemble suites; all prefer to have the heights on the northwest side (after a possible brief flirtation with the northeast), and all seem happy to keep the Atlantic trough away from us through week 2, which would mean a dry but not warm Easter.

Minor update: No curveballs thrown by the GEFS 6z.

The GFS ensemble gives southern Britain a chilly spell during the working week next week. The ECM ensemble gives all of Britain a chilly spell over Easter instead. The GEM ensemble keeps things milder throughout.

Edited March 28, 2023 by RainAllNight

[Howie]

22 minutes ago, RainAllNight said:

Days 7, 10.5 and 14 on the three 0z ensemble suites; all prefer to have the heights on the northwest side (after a possible brief flirtation with the northeast), and all seem happy to keep the Atlantic trough away from us through week 2, which would mean a dry but not warm Easter.

The GFS ensemble gives southern Britain a chilly spell during the working week next week. The ECM ensemble gives all of Britain a chilly spell over Easter instead. The GEM ensemble keeps things milder throughout.

It seriously needs to warm up now, getting tired of the cold 

[Rain All Night]

1 hour ago, RainAllNight said:

Days 7, 10.5 and 14 on the three 0z ensemble suites; all prefer to have the heights on the northwest side (after a possible brief flirtation with the northeast), and all seem happy to keep the Atlantic trough away from us through week 2, which would mean a dry but not warm Easter.

Minor update: No curveballs thrown by the GEFS 6z.

The GFS ensemble gives southern Britain a chilly spell during the working week next week. The ECM ensemble gives all of Britain a chilly spell over Easter instead. The GEM ensemble keeps things milder throughout.

Just to show a dissenting view, the CFS has a trough over the UK for the week covered by the height charts I posted earlier, lol.

Edit: But it doesn't if you look at the CFS charts on Tropical Tidbits rather than the ones on the NOAA/CPC website 

Edited March 28, 2023 by RainAllNight

[Methuselah]

Here's today's Deep Dive. Suitable for any newbies, I'd think. And, just as importantly, things could be better by the Easter weekend: 

 

 

[Rain All Night]

Looking benign from Sunday onwards on ICON and GFS, a welcome change from my perspective, but I can see how those who prefer a bit of drama might be bored by this...

UKMO and GEM let the westerlies and associated rain back in on Tuesday, although the GEM's FI shows this as only a temporary relapse...

I can't see any wintry FIs among those models which have an FI any more.

Edited March 28, 2023 by RainAllNight

[Cambrian]

In a good few runs now, the GFS firming up on a drier spell from early next week. Indeed, that’s looking like a big change in the feel of the weather from day 3 on the 12z GFS ensemble mean, before the coming weekend, 

 

to day 6, after the weekend, 

 

even without the effervescence of the op, a 40mb rise in pressure over just 3 days for the mean. It’s a transformation. 

However, the temperatures don’t respond, and actually go down at the start of April with a northeasterly flow for a few days. Some chilly nights, but during the day it’s no doubt going to feel a lot more pleasant with some bright April sunshine. 

  

A welcome trend toward drying out too, looking a lot drier, with many fewer precipitation spikes from as early as around day 5, which is the same time the op gives up on the rain (for Birmingham shown here), and particularly after around day 8. 

Casting an eye forward to day 12, Easter Sunday, coming into range for a bit of a punt now - the high pressure eases somewhat but there is no return to a cyclonic pattern - the mean chart shows the signal for heights over us and north to Iceland and Greenland holding in place, high pressure all the way to the pole, a surface high pressure of 1020mb encircling the UK and Ireland. 

 

Still no great shakes for temperatures by then either, but slowly climbing to double figure maxima for many, and with light winds and some sunshine, that could make for a very pleasant Easter and a very usable break - crisp mornings and good long, bright afternoons, and perhaps most importantly of all after recent weeks - dry!

[Stuie]

Very nice ECM T168 chart, dry HP. Let`s get some temp rises.

Edited March 28, 2023 by Stuie

[Rain All Night]

2 hours ago, RainAllNight said:

Looking benign from Sunday onwards on ICON and GFS, a welcome change from my perspective, but I can see how those who prefer a bit of drama might be bored by this...

UKMO and GEM let the westerlies and associated rain back in on Tuesday, although the GEM's FI shows this as only a temporary relapse...

I can't see any wintry FIs among those models which have an FI any more.

ECM keeps the Atlantic further away than any of the other four, and produces what I think I've seen you guys refer to as a "North Sea runner"?!

EDIT: That becomes a Good Friday northeasterly in FI, lol.

Edited March 28, 2023 by RainAllNight

[Summer8906]

Really nice GFS 12z.

Spring finally arrives on Sunday, and about time too!

Remarkable how the weather changes almost with the month, which should still ensure the wettest March for a good while, presumably.

[damianslaw]

39 minutes ago, RainAllNight said:

ECM keeps the Atlantic further away than any of the other four, and produces what I think I've seen you guys refer to as a "North Sea runner"?!

EDIT: That becomes a Good Friday northeasterly in FI, lol.

ECM chart above is one of those if only this was winter charts that cold snow lovers long for yet never seem to surface other than in April and May to bring cold North easterlies - wouldn't be surprised if something like this turns up before easter.

The models do suggest a settling down as we move into April, high pressure generally building in and close to the UK with the atlantic trough held at bay, but it all looks a bit half hearted at this range, and no clear signal where heights may end up - perhaps an indication building that they will go to our NW.

None of the models suggest any quick evolution to anything particularly warmer for the time of year. However, what would you prefer, sunshine dry weather, light winds and temps in the 10-13 degree range under an increasingly warm sun, or a cloud leaden airstream bringing rain or drizzle and temps in the mid-high teens, I know what I would prefer the former, the sun makes a real difference by now, and such days to me feel warmer than the latter type of day from now on.