Model Output Discussion - A cold start to Spring?

[Guest]

3 minutes ago, seabreeze86 said:

UKMO day 7 is brilliant great call by Nick.If we not happy with this we in a good place. I think the double reversal is causing us to see things that ain’t the norm the Atlantic is complete in retreat 

It's great for Scottish snow fans, not so much so further south.  Expect further little features and complications to be picked up in the coming days and before you know it we end up with a rather mundane sunshine/wintry showers scenario.  Much to be decided but overall the output this evening has trended away from anything too severe/wintry IMHO.

[Lukesluckybunch]

11 minutes ago, Tidal Wave said:

I think we need to be mindful of what could happen as that very cold airmass meets the Atlantic - can certainly see what CC is alluding to and this could very quickly end up making a bitter north-easterly into a mild south-westerly.  You seldom get such a clean evolution.

UKMO Day 7 keeps it cold but overall the run is not as good as last night if you want cold/snow:

Yes totally agree with you..crucially we have lost them strong heights across greenland and the little shortwaves that keep cropping up are causing mild sectors In between the very cold air,ideally we would like a cleaner source of air from the northeast..having said that if this run went on further I would imagine that very cold air would reach us.

Edited February 28, 2023 by Lukesluckybunch
Adding

[sheikhy]

Very good ukmo12z!!funny how gfs 12z ditches it completely and ukmo picks it up!still a very fine ukmo and i could be wrong but i think ecm is gona be a belter!!!!

[ICE COLD]

Gfs 12mean looks great at T168

[Ali1977]

3 minutes ago, ICE COLD said:

Gfs 12mean looks great at T168

Snowy control too 

[winterof79]

There will be a multitude of disturbances/s waves running from North or East of North that will only appear much closer as is always the case with entrenched cold at this juncture in winter/ v early spring

 

[alexisj9]

22 minutes ago, Tidal Wave said:

It's great for Scottish snow fans, not so much so further south.  Expect further little features and complications to be picked up in the coming days and before you know it we end up with a rather mundane sunshine/wintry showers scenario.  Much to be decided but overall the output this evening has trended away from anything too severe/wintry IMHO.

What time frame are those lows, specifically the first one. If it's after day four, expect it to be weaker, by then.

[Bricriu]

4 minutes ago, Ali1977 said:

Snowy control too 

Would there be the possibility of a polar low within that unstable flow? . I imagine the thickness level would be low enough for one 

[tight isobar]

Complete layer- vibrations through the 12z sets!! And a txt book pv switch east / north east!.. some news making weather increases in likelihood. And the supports throughout the 12 sets should be preety striking.. I’ll quote and snapshot em after the Euro run !!!!!’

[seabreeze86]

Just for fun at this range but the UKMO has a band of snow pushing south on the 12z

[winterof79]

5 minutes ago, Bricriu said:

Would there be the possibility of a polar low within that unstable flow? . I imagine the thickness level would be low enough for one 

I would say most definitely due to the source of air and instability,conditions ripe for development

[Eagle Eye]

Secondary large +VE EAMT likely to cause extension of Pacific jet and cyclonic wavebreaking over North America which is typically good for North Atlantic jet retraction and blocking towards Greenland via RWT induced AWB enhancement.This could potentially form a dipole of blocking to the North. Given MJO staying fairly enhanced in a weakening -VE ENSO state MJO Phase 7/8 with the start of the westerly wind burst into the climbing -VE Nino 3.4 area. Given a cycling more west based -VE EPO cycle and an E US ridge then we could have more chances for cold events up to mid March. Relying on strong MJO Phase and the atmospheric state to remain in the intraseasonal Nino state band (+VE AAM) and w'ly atmospheric drag which cycles around certain areas depending on the RWT. Tropical forcing looks to remain high for now though given the MJO RMM staying around Phase 7-8 and around +2 in terms of RMM 2 strength and mountain torque events. So Wave propagation and jet oscillations suggest zonal wind recovery is unlikely with the mean transport of mass, momentum and energy given the transfer of w'ly momentum via tropical-extratropical interaction under this Nino setup. Frictional torque is likely to repress the mountain torque gain and cause a -VE EAMT event but the SSW appears to suppress that reaction for now.

I realise that's a lot of writing and I kind of just summarised everything.

Essentially, what I expect to happen is that for now we see the first effects of SSW imprinting its effects on the Trop by -VE NAM downwelling (despite non reversal downwelling into the Trop, the Trop and Strat are set up for a reaction anyway) and we see that with the risk of bringing in cold next week (ish) but possibly earlier or later. The exact direction of flow will determine exactly what happens but that depends on small scale permutations where each front has some sort of wider scale effect. Then, we could see a further extension of the Pacific jet and a recycling of the -VE EPO regime but perhaps more west based than last time. Meaning that there is support for blocking to the north to return around mid March. Given typical -VE NAM tripole characterisations of stronger reversals with 1 Upwell and 2 downwells in some or 3 downwells in others as a generalisation; it can be thought of that this one could be similar. Meaning that as the eddies lower down in the Troposphere start retracting, the AWB that caused the norther blocking in the first place may have formed a dipole. If it has then upwelling and Wavebreaking into the <=0 part of the lower Strat is likely and that flushes down another band of weaker zonal winds forcing tropical-extratropical interactions and poleward eddies so downwelling of the -VE NAM is possible. Given the zonal asymmetric response to west Pacific MJO link with AAM budget and the typical response to the SSW I wouldn't be surprised if we did see the upper Tropospheric flow pattern leading surface conditions quite favourably for coldies. With AAM flux converging then we start to see a favourable poleward momentum flux given best MJO convection in terms of Indo-Pacific warm pooling and that grows the strongest extratropical response. A lot is really lining up with the MJO-AAM link with the slow surface frictional anomalies in the tropics leading risk shorter flux in the extratropics and that appears to be linking itself well with the northwards transport of momentum with AAM convergence and the general intraseasonal AAM anomalous movement would suggest the typical response  to the best MJO warm pool in terms of eddies is going to occur here. So we have a double AAM spread with the MJO Indo-Pacific linear time linking. This looks to put tension on eastwards movement in the North Atlantic and drag the jet back. So this is really looking like a sign that this upcoming event may not be it if we can get it all to time together for just before late March though anytime before then is good really if we can get the best fetch in terms of easterly or northerly.

Here's what I mean with the mid-latitudewards movement of the near surface reversal though we won't see if it'll be helpful for us yet.

Though importantly, we need the MJO to time perfectly in this situation for that second setup to be possible. Essentially, the difference between phase 8 and phase 1 is so big that 1 has Nino reactions and the other has Nina reactions.

Sorry if that post was really confusing, it's right at the top of my ability and there's a bit of conflicting when it comes to Indo-Pacific warm pools and AAM links and also whether or not the frictional torque balances out the w'ly's before or after the RWT sets sail.

 

[Ali1977]

1 minute ago, seabreeze86 said:

Just for fun at this range but the UKMO has a band of snow pushing south on the 12z

A heavy one too 

[Climate Man]

3 minutes ago, Eagle Eye said:

Secondary large +VE EAMT likely to cause extension of Pacific jet and cyclonic wavebreaking over North America which is typically good for North Atlantic jet retraction and blocking towards Greenland via RWT induced AWB enhancement.This could potentially form a dipole of blocking to the North. Given MJO staying fairly enhanced in a weakening -VE ENSO state MJO Phase 7/8 with the start of the westerly wind burst into the climbing -VE Nino 3.4 area. Given a cycling more west based -VE EPO cycle and an E US ridge then we could have more chances for cold events up to mid March. Relying on strong MJO Phase and the atmospheric state to remain in the intraseasonal Nino state band (+VE AAM) and w'ly atmospheric drag which cycles around certain areas depending on the RWT. Tropical forcing looks to remain high for now though given the MJO RMM staying around Phase 7-8 and around +2 in terms of RMM 2 strength and mountain torque events. So Wave propagation and jet oscillations suggest zonal wind recovery is unlikely with the mean transport of mass, momentum and energy given the transfer of w'ly momentum via tropical-extratropical interaction under this Nino setup. Frictional torque is likely to repress the mountain torque gain and cause a -VE EAMT event but the SSW appears to suppress that reaction for now.

I realise that's a lot of writing and I kind of just summarised everything.

Essentially, what I expect to happen is that for now we see the first effects of SSW imprinting its effects on the Trop by -VE NAM downwelling (despite non reversal downwelling into the Trop, the Trop and Strat are set up for a reaction anyway) and we see that with the risk of bringing in cold next week (ish) but possibly earlier or later. The exact direction of flow will determine exactly what happens but that depends on small scale permutations where each front has some sort of wider scale effect. Then, we could see a further extension of the Pacific jet and a recycling of the -VE EPO regime but perhaps more west based than last time. Meaning that there is support for blocking to the north to return around mid March. Given typical -VE NAM tripole characterisations of stronger reversals with 1 Upwell and 2 downwells in some or 3 downwells in others as a generalisation; it can be thought of that this one could be similar. Meaning that as the eddies lower down in the Troposphere start retracting, the AWB that caused the norther blocking in the first place may have formed a dipole. If it has then upwelling and Wavebreaking into the <=0 part of the lower Strat is likely and that flushes down another band of weaker zonal winds forcing tropical-extratropical interactions and poleward eddies so downwelling of the -VE NAM is possible. Given the zonal asymmetric response to west Pacific MJO link with AAM budget and the typical response to the SSW I wouldn't be surprised if we did see the upper Tropospheric flow pattern leading surface conditions quite favourably for coldies. With AAM flux converging then we start to see a favourable poleward momentum flux given best MJO convection in terms of Indo-Pacific warm pooling and that grows the strongest extratropical response. A lot is really lining up with the MJO-AAM link with the slow surface frictional anomalies in the tropics leading risk shorter flux in the extratropics and that appears to be linking itself well with the northwards transport of momentum with AAM convergence and the general intraseasonal AAM anomalous movement would suggest the typical response  to the best MJO warm pool in terms of eddies is going to occur here. So we have a double AAM spread with the MJO Indo-Pacific linear time linking. This looks to put tension on eastwards movement in the North Atlantic and drag the jet back. So this is really looking like a sign that this upcoming event may not be it if we can get it all to time together for just before late March though anytime before then is good really if we can get the best fetch in terms of easterly or northerly.

Here's what I mean with the mid-latitudewards movement of the near surface reversal though we won't see if it'll be helpful for us yet.

Though importantly, we need the MJO to time perfectly in this situation for that second setup to be possible. Essentially, the difference between phase 8 and phase 1 is so big that 1 has Nino reactions and the other has Nina reactions.

Sorry if that post was really confusing, it's right at the top of my ability and there's a bit of conflicting when it comes to Indo-Pacific warm pools and AAM links and also whether or not the frictional torque balances out the w'ly's before or after the RWT sets sail.

 

Are you Tamara in disguise?

[winterof79]

5 minutes ago, seabreeze86 said:

Just for fun at this range but the UKMO has a band of snow pushing south on the 12z

Nice feature 

 

[Eagle Eye]

Just now, Climate Man said:

Are you Tamara in disguise?

Ha ha no though I did ask her for some reading on AAM earlier this Winter.

[tight isobar]

Your energy suppliers looking at today’s outs.....

[Snowy L]

23 minutes ago, Ali1977 said:

Snowy control too 

Wow I guess that's what can happen even if you have pesky Iceland shortwaves as long as the Azores High behaves itself and stays far away. Risky but potential for huge snowfalls.

[MJB]

26 minutes ago, Ali1977 said:

Snowy control too 

Blimey a very snowy one 

[Guest]

22 minutes ago, alexisj9 said:

What time frame are those lows, specifically the first one. If it's after day four, expect it to be weaker, by then.

It's not the usual lows coming in from the Atlantic, it's shortwave features that develop as the cold mass of air hits the warmer waters of the North Atlantic.  Take the UKMO 120hrs chart:

A kink in the isobars east of Iceland.  By 144hrs its a more pronounced feature south of Iceland:

By 168hrs its sinking south across the UK as a low spawns:

 

At the very least it's another delay to the properly cold air reaching us, and we know what delays usually end up with.  Models won't pick up on these features until they are in the 168hr timeframe.  That's why seemingly flatlined ensembles suddenly starting going up and down as these warmer sectors get picked up nearer the time.

[nick sussex]

A few years back we had a scenario where the main block went far west but a surface high developed to the ne and kept the UK in colder air .

It was quite unusual at the time . I wish I could remember the date as it was a very interesting set up .

[winterof79]

4 minutes ago, Tidal Wave said:

It's not the usual lows coming in from the Atlantic, it's shortwave features that develop as the cold mass of air hits the warmer waters of the North Atlantic.  Take the UKMO 120hrs chart:

A kink in the isobars east of Iceland.  By 144hrs its a more pronounced feature south of Iceland:

By 168hrs its sinking south across the UK as a low spawns:

 

At the very least it's another delay to the properly cold air reaching us, and we know what delays usually end up with.  Models won't pick up on these features until they are in the 168hr timeframe.  That's why seemingly flatlined ensembles suddenly starting going up and down as these warmer sectors get picked up nearer the time.

Some folk will get snow even though UKMO over does 850s

 

[Kentspur]

10 minutes ago, nick sussex said:

A few years back we had a scenario where the main block went far west but a surface high developed to the ne and kept the UK in colder air .

It was quite unusual at the time . I wish I could remember the date as it was a very interesting set up .

Was this mid to late January 2013?

[That ECM]

9 minutes ago, nick sussex said:

A few years back we had a scenario where the main block went far west but a surface high developed to the ne and kept the UK in colder air .

It was quite unusual at the time . I wish I could remember the date as it was a very interesting set up .

2018? When many had rain hitting freezing surfaces?

[nick sussex]

10 minutes ago, Kentspur said:

Was this mid to late January 2013?

Thanks . I’ll go and check the archives . 

Thanks also to That ECM . Sadly no joy . It’s really bugging me . I will get there eventually!

Edited February 28, 2023 by nick sussex