Model Output Discussion - moving into Winter

[Skullzrulerz]

12 minutes ago, LightningLover said:

Now this is more like it... Take notes ECM and we'll test you later on what you've learnt!

It should be the GFS who should be taking notes, it's been poor over the last few days.

[Weathizard]

That low that initially undercuts our blocking, looks like becoming a very prominent feature between day 8-10, can’t see it going anywhere other than well south of the UK, experience tells you even if the GFS takes it further north in low res that this will go much south with the Jet

[IDO]

The GFS is what I expected the ECM to do at T140+, slow that Atlantic low as it collides with the block, sending WAA north on its eastern flank. 

GFS D9:  ECM: 

The ECM just pushed the low through with no resistance.

The GFS did get a nice cold pool in and is being fed a drip drip of colder uppers from higher up the trough, so the Atlantic low will struggle to brute force the pattern as the ECM did.Undercut most likely with this run. 

[blizzard81]

2 minutes ago, IDO said:

The GFS is what I expected the ECM to do at T140+, slow that Atlantic low as it collides with the block, sending WAA north on its eastern flank. 

GFS D9:  ECM: 

The ECM just pushed the low through with no resistance.

The GFS did get a nice cold pool in and is being fed a drip drip of colder uppers from higher up the trough, so the Atlantic low will struggle to brute force the pattern as the ECM did.Undercut most likely with this run. 

Yep. Remember the atlantic troughs in November all became negatively tilted (same as Nov 2009). When that happens, the following winter atlantic troughs tend to do the same when cold has become embedded in our vicinity. The troughs in the atlantic on day 9 gfs 06z have become negatively tilted. 

[IDO]

JFF: The Asian tPV much better aligned N-S than previous runs, which could if other variables allow, bring a renewed colder flow in FI:

[seb]

Beautiful. GFS kills the low roundabout 236 hours and pushes its remains to the SE without ever coming close to impacting us. Makes much more sense than what the ECM produced earlier. Exactly what you'd expect with that huge area of high pressure blocking the low and also in line with jet (which the ECM's solution was not).

Edited December 2, 2022 by seb

[Radiating Dendrite]

Great charts again - the ECM would likely correct south, models are always progressive with energy against a block. 

We usually say with a cold spell, we have a ticket for the raffle. This feels more like a stash of tickets for the euromillions.

[Singularity]

As little as individual runs really matter at the moment, it's interesting to see the trough extension across Scandinavia from Siberia maintained a bit longer on the GFS 06z.

This implies that the changes to the orientation of the high that we saw for the 00z run are prone to reverting at least a little bit.

There's a connection to the (sub)tropical cyclone being modelled near the Azores; the 06z forces it to peak further west before extra-tropical transition & disruption of its circulation by the cold air to its north. Hence it's a fair bit further south as it heads into mainland Europe compared to the 00z.

[Penrith Snow]

What I like about the latest runs are that they are slowly upgrading the cold spell, normally it’s the other way round!

Not drawing comparisons but there was nothing exceptional in the models in mid November 2010 but they upgraded over time so by the time the cold spell hit it exceeded expectations.

Andy

[IDO]

JFF The GFS op does the same with the second Atlantic low, stalling, WAA eastern flank and rebuilding Atlantic heights for part 2:

This repeating pattern is what we want, not that messy ECM op outlier. Obviously, likely to be another spin by 12z, but this is a great run.

 

[Downburst]

Next week is going to be bloody freezing. Some shock, negative dew points widely Wednesday to Friday at least. That crashing low coming in next weekend is probably not going to be as strong, but even if near that it could cause some heavy snow. 

ECM weather app for Dublin, I mean look at the feels like temps?

Air Mass Friday morning, air still moist and very cool, will feel very cold indeed. I was hoping for less stagnant low pressure and a bit drier air from the north. We shall see, but that's scarf wearing weather that is.

[phil nw.]

Signs from the gefs 850temp.ens graphs that the cold air does gets south of the Uk in the medium term.

A look at the London and Paris ens graphs shows a mean of -5 into London by the 10th and Paris 3 days later.

Good signs that if any battleground develops near the south the cold air would prevail,based on this.

Overall the trend continues for a nicely aligned Scandinavian trough heading our way for the middle of next week.

Plenty of wintery interest to follow.Just waiting to see what disturbances may develop in the flow which won't be picked up yet.

It's all lining up nicely.

[Johnp]

36 minutes ago, Paul_1978 said:

I have to say the output looks very good at face value and synoptically stunning, but latest BBC Weather For The Week doesn’t particularly show any kind of wintry nirvana in the next 7 days. Even next Friday temps are well into single figures across most of the UK. 

I want widespread snow as much as the next person but looks like anything like this is still a week/10 days away at least. 

https://www.bbc.co.uk/iplayer/episode/m001fr7k

Not aimed at you personally, but this post could be copy and pasted each year in the run up to a cold spell. The media are always slow to ramp anything up. 

[Guest]

What a 144hrs mean from the GFS:

Cold pattern becoming entrenched and colder air further south.

[kold weather]

11 minutes ago, Radiating Dendrite said:

Great charts again - the ECM would likely correct south, models are always progressive with energy against a block. 

We usually say with a cold spell, we have a ticket for the raffle. This feels more like a stash of tickets for the euromillions.

Not only that but the ECM peaks thyat low at a really rather deep 943mbs.

That feels far too deep given the position of the low.

The bigger concern is that cold pool aloft shooting SSW gets stronger and stronger in the models and we end up seeing a more signficant LP and with it a much stronger warm sector as well developing. For those further north it should be ok still but we are early season for the south given how absurdly mild it has been and SSTs are still closer to what they would be in mid November (though will be cooling now) which means down here we will need a proper cold shot, none of that moderated stuff.

[nick sussex]

Encouraging to see a little eastwards shift on the GFS 06hrs run .

Theres no chance of the instability missing the UK and it’s not like a northerly toppler which tends to push the coldest air and instability too far east.

 

[Mark wheeler]

Wow , some proper magic charts popping up .

[Battleground Snow]

Nice to see the ensembles trending down, should reduce marginality for south with regards to snow/rain 

[swilliam]

Nice Genoa low in FI - just what we want with corresponding -10s coming into Scotlad

[ICE COLD]

The 6z op still going for it late on

[chris55]

1 hour ago, fromey said:

A some encouraging comments from Ian Ferguson.

Ensembles for Stroud  woohoo lol.

[bluearmy]

6 minutes ago, kold weather said:

Not only that but the ECM peaks thyat low at a really rather deep 943mbs.

That feels far too deep given the position of the low.

The bigger concern is that cold pool aloft shooting SSW gets stronger and stronger in the models and we end up seeing a more signficant LP and with it a much stronger warm sector as well developing. For those further north it should be ok still but we are early season for the south given how absurdly mild it has been and SSTs are still closer to what they would be in mid November (though will be cooling now) which means down here we will need a proper cold shot, none of that moderated stuff.

The eps control also built that low to the sw but not quite as strong as the op so it came in a more southerly latitude - still took the pos uppers to the midlands 

and it was on the control 12z yesterday too 

caution for those wanting that ne flow - with the sst’s where they are, that would be nerve racking for lowland eastern areas - the western side would be ok re snowfall if trough appear as the air would have time to cool. The stagnant cold trough aloft  (as we saw in dec 2010) would be safer. Once the cold is embedded in, the ne flow becomes a little safer.

Edited December 2, 2022 by bluearmy

[MattH]

Morning.

The overall evolution remains consistent, which now carries high confidence, with regards to the blocking high evolving over the coming days, initially bringing a lower theta-w airmass from the E this weekend and then transfering to the NW of the British Isles into next week.

The issues with regards to the low over Biscay and how areas of vorticity would evolve and interact with this low to potentially develop it and obviously track further northwards has also now been resolved as well, for the most part, and with the likes of the UKMO model, from days back, clearly being followed by the likes of the GFS which wanted to bring this feature further north. Therefore, there is a 2-stage evolution to the foreast over the next 7 days and that is this weekend's colder trend and then the 'main event' from next Tue/Wed onwards. 

The details, of course, will follow in time, especially regarding any embedded troughs and possible polar lows, especially given that some model data drops 500mb temperatures to down to near -35C to -40C to the N of the British Isles, through the Norwegian Sea. The other important factor will be SST's. While these will modified the boundary layer and air mass, to an extent, it is the intensity and depth of convection that could be quite extreme with squat winter-time CB's widespread. The lapse rapses will be very steep and intense wintry showers seems a good shout for the second half of next week, but, again the developments and details on that will follow, particularly if the flow remains strong enough, as apposed to becoming more slack.

The -ve EMAT event currently IMO is not a negative to the evolution, it would be if we were within a zonal, entrenched W'ly flow, as it would add fuel to the W'ly fire, that is not the case. The amplification of the N Hem is extreme and the jet retraction that follows the -ve EAMT will help to fuel this amplification where it is in evidence. I wanted to highlight some key features, just using the 06Z GFS looking ahead that are important to late next week;

1) We can see a split vortex to start with, obviously the large vortex over Russia and Asian is not of any real significance, but the one over Canada is. Normally, with a more zonal jet stream this deep cold over Canada would often be fueling the jet stream over the NE of the USA, but, again that isn't the case.

2) Note the extremely fractured jet stream pattern modelled, that wouldn't look out of place in summer to be honest and, linked to the slow-moving vortex over Canada is our Greenland block. What we can see from that slow-moving vortex is that on the eastern flank of it is significant WAA (Warm Air Advection), highlighted by the 850mb temperature anom plot in the middle. WAA into the western side of a block helps to build it/sustain it.

3) It really is like the 'perfect storm' for the opposite of a zonal, +ve NAO regime, with the WAA feeding the Greenland block looking ahead.

Without look too far ahead where we go from this is very hard to see, will the block eventually decline, one would expect so, at least for a time, but there is then still the expected development of the MJO progressing through pheases 4-5-6-7 in the coming weeks and, IMO, with likely increasing amplitude as well, then as some have already discussed, we've got a strat vortex that is getting beat-up from below and potentially from above as well with wave 1 activity.

I wouldn't even "worry" about what happens long-term at the moment anyway, which is roughly mid-December onwards, there is that much to get through in the next 7 to 14 days to keep both amateurs and pros alike both happy and busy!

Fascinating to see all this play out after long-standing predictions from both the key seasonal models, but also all the usual teleconnections and drivers as well going back weeks, if not months.

Cheers, Matt.

[kold weather]

2 minutes ago, bluearmy said:

The eps control also built that low to the sw but not quite as strong as the op so it came in a more southerly latitude - still took the pos uppers to the midlands 

and it was on the control 12z yesterday too 

caution for those wanting that ne flow - with the sst’s where they are, that would be nerve racking for lowland eastern areas - the western side would be ok re snowfall if trough appear as the air would have time to cool. The stagnant cold trough aloft  (as we saw in dec 2010) would be safer 

I almost view this as a primer blast of cold (like the last week of Nov 10 was) that should allow things to get properly cold if we can keep or tap into the pattern again down the line. Its hard to imagine with such a strong burst of northern blocking that we won't get another blast of it down the line, most winters with a strong block like this will usually see at least another 1-2 such blocks develop, even if they aren't quite as strong as the first one.

I think there is a real good chance for snow event further north, I'm not convinced it will be the case further south though just yet.

[ICE COLD]

And just for good measure the 6z goes for another greenie high at the end . What a run