Winter Model Discussion - 11/01/13 00z Onwards

[WhiteFox]

If one believes there is some trust in the later stages of these model runs, then it begs the Q what effect is the Strat warming of a few days ago ACTUALLY going to have, esp if the PV is firing up again? It seems to go against what was meant to happen.

OR am i just being a bit stupid here?

Not at all! The difference that seems to have been picked up since the charts showing HLB on 08/01 is that the jetstream has kicked into life. Although SSW may increase the likelihood of HLB, I have no idea if it has enough effect to counteract a surge in the power of the jet. I think the differences we are seeing in HLB between now and three days ago is due to the strength of the jet not allowing time for a substantial block to form. The 6z has developed the jet streak and powered it straight across the Atlantic flattening everything in its path. On the 0z there was a slightly more ESE flow which allowed colder air to hang on. If the GFS has overestimated the strength of the jet then we will possibly see it tracking further south. It seems however that the ECM has also picked up on a strengthening of the jet hence its trend towards the jet coming closer and then finally over the top of the UK. This trend has been evident over the past few days on the ECM as we have seen the charts change from strong blocking to the north with the jet well to the south, through weaker blocking giving Low Pressure systems coming closer and delivering snow, and now we see the jet tracking to the north and sinking the high so that it ends up to the south.

I suspect that with a weaker jet we would see better blocking and this is normal in any winter. Given that many strat observers have said that the main effects will not be felt until later in the month I think we are looking at a fairly standard winter cold spell for the moment.

[stainesbloke]

Well some of the more cautious folk did warn yesterday that there was little margin for error and any unfavourable shift could easily lead to the pattern tracking further north as opposed to south, could this be what we're currently seeing?

In a word, yes. Although until the jet actually decides which way it's going to go we won't know with any degree of certainty and with the SSW filtering in things will no doubt change again.

[Dean E]

Like others have said, I believe the models are overdoing the polar vortex but a far way.

The SSW is now approaching record breaking levels in nearly all stratospheric levels, while the tropics stratospheric temperatures are reaching record low levels. With this data only just coming in, I believe it will take the models a little more time to engage this.

Pointless looking at anything past next Wednesday in my opinion.

(Sorry for the lack of charts, always difficult on mobile)

SM

[Bristawl Si]

Hopefully just answered your question.

Yes thanks.

Am i correct in saying that for those of you that've been studying Strat warmings and associated research these past couple of years the following has been pretty much proved:

The effects of any Strat warming in the NH will disrupt the PV that are likely to cause its splitting, breaking up, etc

This will cause severe cold events in parts of the NH BUT it's hard to predict exactly where.

But Qs still remain, even for those who've been studying this for a number of years, as to EXACTLY where the effects will be felt AND

for how long after.

Therefore, am i right in saying that a SSW or series of Strat Warming events in a short period of time will NOT guarantee cold and snow for our tiny island or do NOT guarantee long spells of cold, as opposed to a 2-3 day cold snap?

Cheers - fascinating stuff

Edited January 11, 2013 by Bristle boy

[Frosty.]

I don't buy how the gfs 06z flattens the pattern out after midweek and pushes us into a wild spell of mild/cold zoneality. I expect something more substantial next week in terms of a very wintry spell for the next 7-10 days at least.

[Methuselah]

The Jet may well 'kick into life', WF? But, as yet, it's only one possible model prediction. One of very many!

[BLAST FROM THE PAST]

The models today aren't any better than they were yesterday so we still have no real consensus going forward. There is going to be assaults from the Atlantic and in situations like this the further E/NE you are the more likely cold continental airmass will remain influential but thus it will wax and wane over the BI and Ireland. Maybe this is the overall idea of RJS where he doesn't see rock soild blocking and core of cold spell until February.

I don't buy yet a 1055 or 1060 arctic/ GHP to control us but I believe it will increase it's strength rapidly and influence last 8-9 days of Jan building rapidly as we head to turn of month, and inbetween then and now high risk snow to rain to snow situations, and lots and lots of it.

I'm going to step back and view the models on Monday and see where we are, may take a peak or two, but there's lots more up and downs in our locale to come.

BFTP

[chionomaniac]

The Jet may well 'kick into life', WF? But, as yet, it's only one possible model prediction. One of very many!

I think we are right to be wary of any strong jet stream that crosses the Atlantic. The strength and position af the Candian vortex is likely to determine though what leave the eastern US but this should weaken across the Atlantic ( not strengthen as is usual)

[WhiteFox]

The Jet may well 'kick into life', WF? But, as yet, it's only one possible model prediction. One of very many!

This is very true and I don't back any particular outcome after 96 hours. I'm a big fence-sitter! What I will say is that all the models seem to have picked up on a strengthening jet over the past few days; just how strong and where it goes is open for debate...

[Frosty.]

The Jet may well 'kick into life', WF? But, as yet, it's only one possible model prediction. One of very many!

The Gfs 06z just kicks into default mode after midweek and I don't think that will happen, I expect a better undercut of the block, much more like the gfs 00z. Some parts of the uk will have significant accumulations through next week and all parts will have ice days and severe frosts.

[BLAST FROM THE PAST]

Not at all! The difference that seems to have been picked up since the charts showing HLB on 08/01 is that the jetstream has kicked into life. Although SSW may increase the likelihood of HLB, I have no idea if it has enough effect to counteract a surge in the power of the jet. I think the differences we are seeing in HLB between now and three days ago is due to the strength of the jet not allowing time for a substantial block to form. The 6z has developed the jet streak and powered it straight across the Atlantic flattening everything in its path. On the 0z there was a slightly more ESE flow which allowed colder air to hang on. If the GFS has overestimated the strength of the jet then we will possibly see it tracking further south. It seems however that the ECM has also picked up on a strengthening of the jet hence its trend towards the jet coming closer and then finally over the top of the UK. This trend has been evident over the past few days on the ECM as we have seen the charts change from strong blocking to the north with the jet well to the south, through weaker blocking giving Low Pressure systems coming closer and delivering snow, and now we see the jet tracking to the north and sinking the high so that it ends up to the south.

I suspect that with a weaker jet we would see better blocking and this is normal in any winter. Given that many strat observers have said that the main effects will not be felt until later in the month I think we are looking at a fairly standard winter cold spell for the moment.

There's a chain of thought that HP systems control the positioning of the jetstream and not the other way round? The jetstream overall over coming weeks will be shifting south as a general rule IMO.

Re the strat comments from members, if it isn't getting felt in the troposphere now then the approaching set up is and added bonus? I'm not so sure it isn't now being felt.

BFTP

[Geordiesnow]

Really interesting outputs, I think the ECM is cleary the best for cold but the UKMO is perhaps a little better than one may think when first looking at it.

In general though, no matter how much SSW there is, if a piece of PV coming out of Canada is very strong and heads into the Atlantic then surely that can override everything which is what the GFS is perhaps hinting at?

In general also, the blocking on the face of it is not very strong so we do need a bit of luck to fall our way and just hope the SSW will start to effect the outlook in a positive way for cold lovers because even the slightly easterly flow for the weekend has downgraded somewhat in terms of its wind strength.

Lets hope after all this, any snowfall is not limited to just a few places here and there.

[Timmytour]

Just a question on the SSW to either reinforce or alter the way i currently regard it...

Is this very simplistic view of it correct....it will help displace the PV so that chunks of it fall over the Northern Hemisphere which gives us a good chance of getting a cold shot from one of these chunks. However, at the same time, it allows areas of warm air to drift up towards the Arctic. Much as we'd like to get caught in a cold chunk getting displaced downwards, there's no guarantee that we won't end up sitting in the middle of the warm air drifting upwards.

This winter's been like trying to play the perfect game of Jenga.... it looks absolutely fantastic until someone decides that perhaps it's possible to pull one more block out.....

Edited January 11, 2013 by Timmytour

[MisfitDog3]

I think we are just going to have to get our heads around that there are going to be changes coming and going in mid-FI and full on FI which don't come to pass. It reminds me of my weather station when there is a large High Pressure in place. Marginal changes in pressure and short run trends as the High moves around foxes it into forecasting imminent changes asthough a Low were approaching. The High moves again and the pressure pattern reverts and so on!

The next week is going to be fascinating. Personally I really think the horizon on reliable forecasting is the shortest it's been for a very long time. Perhaps as low as 72 hours.

[No Balls Like Snow Balls]

The 06z short ensembles are out. The mean 850c doesn't reach above -5c until Thursday (London), the op run is slightly warmer than the mean at this same time. Looks like cold spell cold last until at least Thursday perhaps. OP run is a outlier on the 18th.

Edited January 11, 2013 by No balls like Snow Balls

[SMU]

Last update-

look at what the GFS is trying to do with the shortwave at 144 - move it EAST through the UK & flatten the pattern-

ring any bells??? only yesterday 00z was the GFS doing the same thing with our low-

watch for these developments this afternoon-

120- westward corrections & pressure back building towards iceland behind the shortwave that dives south around 130- here is what I expect to see-

http://modeles.meteociel.fr/modeles/gens/run/gensnh-10-1-150.png?6

Something like that with the wedge over eastern iceland

S

[bradymk]

Notice how GEFS has got good agreement for amplification and mid atlantic ridge at t300. I know its FI but interesting that nearly every single member goes with this,

Edited January 11, 2013 by bradythemole

[Methuselah]

There's a chain of thought that HP systems control the positioning of the jetstream and not the other way round? The jetstream overall over coming weeks will be shifting south as a general rule IMO.

Re the strat comments from members, if it isn't getting felt in the troposphere now then the approaching set up is and added bonus? I'm not so sure it isn't now being felt.

BFTP

My feeling is that, even though the SSW is affecting the weather right now, the models just don't know what to do with it? The situation must be as new to them as it is to us...

[kold weather]

My big problem Steve is I remember a very similar looking evolution with regards to how the vortex behaved in the December cold spell, with how the vortex spewed out too much energy and flattened everythong. Back then there was decent agreement orginally on a Greenland high being present, but that eventually downgraded to nothing....exactly what seems to be happening now.

Synoptically its a tough call, we may end up with abit of a no-mans land set-up before the atlantic tries to flatten everything out. looking at the way the models have reduced the Greenie to nothing now, we'd probably have a far greater chance of keeping decent cold if we go the ECM route and hope we still get a good enough undercut to keep it propped up.

[ukpaul]

Really interesting outputs, I think the ECM is cleary the best for cold but the UKMO is perhaps a little better than one may think when first looking at it.

In general though, no matter how much SSW there is, if a piece of PV coming out of Canada is very strong and heads into the Atlantic then surely that can override everything which is what the GFS is perhaps hinting at?

Reading the strat thread (and maybe Chiono or someone could elaborate), any model which puts together a strong polar vortex in the medium term, is going against the positioning of the two sections of PV that now exist, the elongated Siberian part and the Canadian part which is tightening and being pushed west.

As such the ECM ignores this and maybe the GFS does too.

The question is, can it logically happen the way that this mid term output is suggesting?

[WhiteFox]

There's a chain of thought that HP systems control the positioning of the jetstream and not the other way round? The jetstream overall over coming weeks will be shifting south as a general rule IMO.

Re the strat comments from members, if it isn't getting felt in the troposphere now then the approaching set up is and added bonus? I'm not so sure it isn't now being felt.

BFTP

I think you're right. But I also think it may be the case that the blocking can't establish in the first place if the jetstream is too strong. May be very wrong and I'm not sure how the cause and effect works with regards to the jetstream and blocking, so I'm just going for what seems to be happening. And yes, in general the jetstream would be expected to head south anyway as we move into the second part of winter.

[Glacier Point]

Models exhibiting shocking inter-run and intra run continuity, and that's just the ensemble means !

The only constants that stand out here when assessing the next 10-14 days:

- troughing signal for Europe;

- below average signal for Europe;

- general signal for +ve height anomalies to our north and NE.

Beyond that, don't bother attempting to place any value in model solutions, of any type. A good time to be able to put non-NWP assessment alongside the myriad of options here. With angular momentum increasing off the back of tropical convective waves in the Pacific, we should see the above general synoptic as the benchmark.

[danm]

My big problem Steve is I remember a very similar looking evolution with regards to how the vortex behaved in the December cold spell, with how the vortex spewed out too much energy and flattened everythong. Back then there was decent agreement orginally on a Greenland high being present, but that eventually downgraded to nothing....exactly what seems to be happening now.

Synoptically its a tough call, we may end up with abit of a no-mans land set-up before the atlantic tries to flatten everything out. looking at the way the models have reduced the Greenie to nothing now, we'd probably have a far greater chance of keeping decent cold if we go the ECM route and hope we still get a good enough undercut to keep it propped up.

I think the difference now compared to December is the SSW. Back in December it was much more plausible that the pattern could and would flatten and the polar vortex would reform. That scenario looks less plausible now.

[Summer Sun]

06z ensembles

[bobbydog]

ok, been trying to get my head around the wide model variation and based on available information and my (limited) understanding of it, i came up with this-

normally, the stratosphere maintains a consistent 'shape' and any variations are over a relatively long period of time. when the data is input into the models, the strat data is also fed in and the models include this in the output. therefore, run to run, the strat data will have changed very little so the models concentrate on the troposheric changes, on the basis that the strat will change very little over a period of time.

however, during an SSW, the strat changes very rapidly, therefore by the time of the next run, the strat data will also have changed. bearing in mind that the stratospheres effects on the troposphere are relatively unknown compared to other teleconnections, also the effects are very variable and not directly correlated, making it difficult for the models to predict any future effects whilst the strat is in a dynamic state. each model will have a slightly different 'take' on how the stratosphere might change, therefore this extra data will increase the variability between the models as they each try to work out how the rapidly changing stratosphere will affect the troposphere, alongside trying to predict the usual troposheric changes.

hence the large differences between each subsequent model run and the large divergence between each of the models the further we go into the forecasting range

i think that makes sense......!