Model Output Discussion - 18z 31/10/15 onwards

[bobbydog]

I'm not impressed by the GFS output at all. Yes there were some improvements on the 18z but ultimately it's not enough. Still the 0z is to come before the ECM updates but I'm firmly in your cautious camp for the time being.

i find your lack of faith disturbing...

[blizzard81]

Well, I did forecast a cold spell for the final third of Nov but not what the ECM op has in mind. I have been an avid watcher of the model output over the last 13 years and I know all too well the over amplification bias the ECM is prone to in the Greenland locale. This has been all too evident over the years. Indeed it seems to be the achilles heel of the ECM in winter and all too often the GFS trumps it in these situations. For this reason, I am extremely cautious about the recent ECM op's. Like I say, cold spell last third of Nov but as severe as ECM????

[Cumulonimbus Tower]

It's not new, but it is the nirvana wave break and can occur prior to the upper strat vortex intensification reaching the trop. Tony and I have been waiting to see of this would occur, as there was a small chance this November and because of this chance had not released an early winter forecast preliminary. I had pretty much ruled it out last weekend though......still........

Sorry Chionomaniac, whilst things are quiet, and if you have time,  is there any chance you could put some of your posts into lay person speak, just so we can get a handle on what people are hoping for and what in your opinion might be spoilers? I understand the depth of atmosphere etc. but not quite how this relates to nest weekend and what might or might not happen.... Think of higher GCSE or lower A level meteorology terms  

[Cheshire Freeze]

GFS control turns into a stunner in FI....very akin to the ECM but delayed a couple of days

 

[Mucka]

ECM London 12z ensembles to compliment Fergies post

 

 

In comparison with the ooz suite the cold cluster is more obvious and the milder runs fewer.

[BlueHedgehog074]

Some quite amusing similarities between this chart from the 18Z GFS and the one from 19th November 2013:

The shape of the ridging in the Atlantic is nearly identical in both with a bumpy flow from the North-North-West. Though there are some differences such as tonight's chart being a bit more amplified, plus the 500mb heights to the East of the UK are lower with more pronounced European troughing. The reason I brought this up was because that particular chart from the GFS tonight reminded me of that November 2013 cold weather setup (and the one which did sort of go wrong thanks to some sneaky little Lows/Shortwaves around Southern Greenland preventing the cold spell being more notable, despite the fact some places did receive wintry weather). Clearly, even should a similar evolution verify, there's no guarantee it would follow what happened 2 years ago since no two weather patterns are exactly the same. It guess it is as some people say really, ensuring that for the cold weather enthusiasts, the ridging around the Canadian area behaves itself and backs far enough East into the Atlantic and/or Greenland area giving the Western UK Low Pressure systems a good kicking into the nearby continent (while stamping-out the European ridging) and drag chillier air down from the North or East. It's always possible, just like on that JMA run, that the Atlantic Lows get stuck to the South-West of the UK and it then becomes the Greenland High's double agent by maintaining some kind of ridging over Europe. And thus preventing snow shields in the UK getting blasted apart.

[ItNeverSnowsInWindsor]

ECM London 12z ensembles to compliment Fergies post

 

 

In comparison with the ooz suite the cold cluster is more obvious and the milder runs fewer.

Nice drop from above average to below average temperatures! As long as the low heights keep away from South Greenland than we're in for more fun and games!

 

[chionomaniac]

Sorry Chionomaniac, whilst things are quiet, and if you have time,  is there any chance you could put some of your posts into lay person speak, just so we can get a handle on what people are hoping for and what in your opinion might be spoilers? I understand the depth of atmosphere etc. but not quite how this relates to nest weekend and what might or might not happen.... Think of higher GCSE or lower A level meteorology terms  

Ultimately the strength of a mature stratospheric vortex will ultimately overwhelm any tropospheric high latitude blocking. The vortex during winter can weaken from tropospheric wave activity that rides up to the top of the stratosphere and will weaken and warm the stratosphere from the top down. This may or may not propagate down to the troposphere.

 

However, there is also a scenario that can occur in early winter, before the strong upper stratospheric vortex is 'felt' at the troposphere, where wave breaks from anticyclones such as a Greenland high can be strong enough to disrupt the lower stratosphere and create a split from the bottom up. This can lead to the type of scenario that the ECM is showing tonight. If the wave activity is not strong enough then the lower stratospheric vortex is not disrupted or split sufficiently and any block will not form or is quickly overwhelmed - more in line with the GFS 18Z output.

[Cheshire Freeze]

Just for fun....you don't see many charts like this!

 

 

[damianslaw]

Lots of interest in the models this evening - many are certainly showing a pattern change to something substantially cooler as we are invaded by air of polar origin.

 

Our weather has a habit of changing dramatically when locked into an extreme spell of duration... think of those spring switcharounds we see.. conditions of late have been exceptional from a mild perspective, unusually sustained...I'm not surprised to see such a potential switch occurring..there is definitely a feeling things are not normal service right now...many many similarities to how things felt in Nov 2009.. which too was anomalously mild and exceptionally wet in these neck of the woods at least.

[Singularity]

For a while I've been thinking that the best way to hit the vortex this winter would be some wave 1 activity in association with that enhanced (by snow cover advance) Siberian High during the earlier part of the winter, followed by wave 2 activity later in the season (supported by the El Nino atmospheric background) that hits the vortex right in the stomach, so to speak.

 

This talk of a 'nirvana wave break' the likes of which we saw in 2009 or 2010 is a whole other ball game, though. Despite still being an outside chance, one has to wonder how such an event would interact with a record-strong El Nino, in terms of where the fragments of tropospheric vortex would end up.

 

Would I be right in thinking that the upper strat. vortex would remain largely unscathed and work down to the surface after 4-5 weeks? It seems like that sort of thing occurred in Dec 2010.

 

Anyway, we might well have another 'That ECM' on our hands so... best wait and see how things evolve over the next few days!

[Cheshire Freeze]

Would I be right in thinking that the upper strat. vortex would remain largely unscathed and work down to the surface after 4-5 weeks? It seems like that sort of thing occurred in Dec 2010.

 

 

 

I would think that would depend on whether there was a warming of the strat thereafter? There must be a route to get a sustained wintry spell like '62-'63

[fergieweather]

Seems inconsequential compared to Paris... but by way of quick update, GloSea5 and MOGREPS both now agree on several days colder weather post-20th onwards. Smaller probability (10%) more protracted/blocked. All eyes on whether the channel low retains support (ie as it does presently in ENS). Update tomorrow.

[Cumulonimbus Tower]

Ultimately the strength of a mature stratospheric vortex will ultimately overwhelm any tropospheric high latitude blocking. The vortex during winter can weaken from tropospheric wave activity that rides up to the top of the stratosphere and will weaken and warm the stratosphere from the top down. This may or may not propagate down to the troposphere.

 

However, there is also a scenario that can occur in early winter, before the strong upper stratospheric vortex is 'felt' at the troposphere, where wave breaks from anticyclones such as a Greenland high can be strong enough to disrupt the lower stratosphere and create a split from the bottom up. This can lead to the type of scenario that the ECM is showing tonight. If the wave activity is not strong enough then the lower stratospheric vortex is not disrupted or split sufficiently and any block will not form or is quickly overwhelmed - more in line with the GFS 18Z output.

Perfectly weighted, nice one, thanks!

[Cheshire Freeze]

Seems inconsequential compared to Paris... but by way of quick update, GloSea5 and MOGREPS both now agree on several days colder weather post-20th onwards. Smaller probability (10%) more protracted/blocked. All eyes on whether the channel low retains support (ie as it does presently in ENS). Update tomorrow.

 

Thanks for that Fergie, will be interesting to see if that 10% chance can increase over the coming days.

[Mucka]

The details will change but GFS getting on board for the ride. 

 

 

Cut off Atlantic low is the killer but this is a long way from yesterdays 00z

 

 

GEM comes up with a huge Atlantic block.

 

 

Blocking patterns seem to be trending and it looks very likely we will get at least a 3 day cold snap out of this but not nailed on yet.

Hopefully come Monday we will be worrying about how cold, how long and how much snow IMBY rather than whether a decent blocking pattern will set up.

Oddly the MetO update is exactly the same as yesterdays forecast with average/slightly above average temps

 

Edit.

Even though GFS doesn't quite get there it is still chilly and comes up with a reload in FI

 

Edited November 14, 2015 by Mucka

[joggs]

The suite that we can view has come about this change the last day or two.What I want to know is,has it been the same for you guys Fergie?

And also jh,have the charts you use been showing this over 3 days?

Or anybody else using different models/charts etc?

Intrigued.

[Newberryone]

Not too sure last evenings state of euphoria, albeit cautious, among model watchers will be repeated this morning courtesy of the Ecm 00z. Cold flow looks like been shunted east relatively quickly on this run. Anyone for a classic toppler!!    

Edited November 14, 2015 by Newberryone

[Captain Shortwave]

The general theme on this mornings updates is some sort of cold plunge arriving during next weekend. This courtesy of the heights over Europe retrograding in response the the ridging over NE Canada.

Shown by the ECM, but reflective of the other outputs this morning.

 

The ECM of last night has not been repeated so at this time an Atlantic ridge is more likely than some form of cut of high to our north west, no point debating whether it will topple or not yet as that is too far away and at this time we should concentrate on the 5-8 day range where the initial potential northerly is currently being modelled. 

[IDO]

The GEFS are on side with a couple of colder days from the 21st and then we lose the mild and the mean then keeps it near the average: 

 

At D8 all models agree that the flow slows allowing a HP cell to get to the mid-latitude in the W.Atlantic:

 

  

 

The HP system forms early so it pushes the colder uppers across the Atlantic with the flow, so that mitigates the strength of those cold uppers time they reach the UK. All models have the cut off upper low and how that acts will effect that MLB. All three handle it differently so early days as to how this meridional flow develops. I would be surprised if this was anything more than a transitional wave in the flow. 

 

As with the last couple of years it is the US (big country so obvious really) that seem to benefit from these cold incursions: 

 

So high confidence in a cold shot at least for three areas of the ML, with this three wave NH interlude. How much of that cold will the UK see?

 

 

 

 

 

 

[Ali1977]

If the GEM proves correct then we are in for an epic last week of Nov and beyond...Sadly, that amount of blocking isn't supported by other models, not to say they won't over the next few runs.

[Liam J]

If the GEM proves correct then we are in for an epic last week of Nov and beyond...Sadly, that amount of blocking isn't supported by other models, not to say they won't over the next few runs.

Well that would be a turn up for the books if the GEM was leading the way... But thankfully plenty of potential across the main models. 

 

Still some worrying rainfall totals this morning from the 00z NetWx-SR.

 

 

 

Edited November 14, 2015 by *Sub*Zero*

[Man With Beard]

Colder weather on the way? Seems likely now, though I should issue the public health warning that in such dramatic pattern changes, the cold does not always get as far south as predicted - any "channel low" could easily become a "Midlands low" as heights to the south remain slightly more robust.

Even if some of the best charts come off, snow potential would not be a given either, being still fairly early in the season - northern areas and high ground would qualify for sure, but for lowland areas I feel the air needs to be a touch cooler, particularly south of Lancs/Yorks. Maybe a nighttime dusting could be achieved if everything is right.

Frost, however, would be widespread. And actually sunshine levels could well rise after our long "warm cloudy" spell.

So lots of interest but to get comparisons with Nov 2010 need even better synoptics

[fergieweather]

The suite that we can view has come about this change the last day or two.What I want to know is,has it been the same for you guys Fergie?

And also jh,have the charts you use been showing this over 3 days?

Or anybody else using different models/charts etc?

Intrigued.

It came more into focus quite quickly as models dithered. Interestingly, a few days ago on 8 Nov, colleagues and I discussed what was then a minority (& thus unlikely, at the time) cluster in EC ENS right at end of run... compare and contrast it, shown here, now to broadscale 00z DET output:

[Iceaxecrampon]

00z real eye candy for coldies at T+186 Saturday 21st November.

 

 

 

Similar to November '88 and '89.

 

In the meantime some impressive rainfall totals this weekend especially Cumbria.

 

Ian