Winter Model Discussion - Cold Hunting -23/12/12

[Jason M]

Further trending in the ensembles for much colder weather. Zonal horrors are still present but in much smaller numbers.

Some northerlies, easterlies and some bizzare charts as well as a few zonal runs. 100 per cent improvement today, and bearing in mind that were not exactly in a great place tonight that just shows how awful things were looking on Thursday evening.

The key is a greater push north of pressure in the medium term. Once the ridge gets towards Iceland we begin to get into scandi height rise territory. Others can better argue the cause of this :-)

Hopefully things will continue to improve in the morning although no doubt we will get some set backs. Personally I hope the cold runs are not reflected in the opps just yet. The stress of tracking a cold spell from 300 hours out would surely be too much :-)

If I were GP or one of the strat guys I'd be feeling quietly pleased with myself tonight as whilst I'm amongst the sceptics, the ensembles seem to be trending in line with the dates suggested. Something is clearly afoot.

Jason

[La Bise]

Are EML and Jason talking about the same models above?

[ITSY]

one is short term centric other is long term. different areas so different results.

[LomondSnowstorm]

one is short term centric other is long term. different areas so different results.

I honestly don't see any reason for pessimism tonight, in the medium term things are starting to shape up as they need to and are the building blocks for mid month are being laid. Keeping expectations low for the next few days will be key, as will continuing to take every chart with a large pinch of a salt given how much they're likely to struggle with the stratospheric warming. We have a long way to go before we're likely to see something concrete emerging on the charts, so bags of patience are still required, but an absolutely fascinating period coming up whichever way things go.

Edited December 30, 2012 by LomondSnowstorm

[EML Network]

I think my post was born out of frustration tbh, I have to confess I've not really looked at the various GFS runs in much detail tonight, so If there's a lot of runs that point to an improving picture for cold then I could well be having a ''glass half empty'' moment

[Panayiotis]

Definite trend for temperatures at 850hPa (~1500m) to decrease after the high next week, so far the mean looks as though the temps near the surface will be average/slightly below average, also there is only one member passing the 5C (past the 11th) on the 18z whereas on the 12z there are 4 members passing the 5C(past the 11th), small steps but in the right direction.

12z (left) 18z (right) For my area (Cardiff)

Edited December 30, 2012 by Panayiotis

[AWD]

ECM De Bilt ensembles show a gradual cooling trend with some colder members in FI;

[Jason M]

Are EML and Jason talking about the same models above?

The key is to look across all the evidence available. Compare all current models and the last few sets of model runs and look for trends. On Thursday night the trend had been downhill for the best part of a week. Indeed I said on Thursday evening that the GFS run that evening was in its own way as extreme towards warm weather as the fabled jan 87 run had been for cold weather.

Since then, the pressure build from the south has been modelled several hundreds of miles to the west out in the Atlantic and the push of associated warm air has been progressively being modelled to reach higher and higher latitudes. You will often see this referred to as warm air advection WAA. If WAA gets far enough north to our west you will tend to get the opposite effect to our east with CAA thereby a high pressure cell can build which if in favourable position leads to an easterly. alternatively if a low forms it can bring an initial northerly shot. The dynamics are more complex than I could explain, but the trend is towards one of these scenarios.

You won't see this in the opp runs at present, but its much more evident within the ensemble suites.

Of course it may all change for the worse in the morning, but the changes are occurring in line with strat changes and whilst these are outside my understanding, I'm not a big believer in coincidence and i therefore tentatively conclude something interesting might be about to happen.

Jason

[Panayiotis]

In the shorter term,its looking likely that people in the Isle of Man,around the Bolton area, Highlands of Wales and Scotland may see some snow tomorrow/tonight..

Edited December 30, 2012 by Panayiotis

[kumquat]

In the shorter term,its looking likely that people in the Isle of Man,around the Bolton area, Highlands of Wales and Scotland may see some snow tomorrow/tonight..

As Dave (TEITS) noted last night, I think, and as I've touted for the last few weeks, NAE seems out of sorts on its ppn predictions. Wouldn't be surprised to see no snowy ppn at all in the UK but a fair amount in Ireland / N. Ireland at that timeframe. I'd like to push it all east as that seems the trend of the NAE currently but the uppers won't support it.

[Panayiotis]

As Dave (TEITS) noted last night, I think, and as I've touted for the last few weeks, NAE seems out of sorts on its ppn predictions. Wouldn't be surprised to see no snowy ppn at all in the UK but a fair amount in Ireland / N. Ireland at that timeframe. I'd like to push it all east as that seems the trend of the NAE currently but the uppers won't support it.

Oh I didnt know,I thought it was regarded as more accurate and reliable?

[kumquat]

Oh I didnt know,I thought it was regarded as more accurate and reliable?

Yeah, it absolutely (and normally) is. It's a higher res model in the short term, I believe. It just doesn't seem to be coming up to par recently

[Panayiotis]

Perturbation number 2 has caught my attention in todays runs, as you can see the 18z run for 384hrs produces this lovely Greenland high, I remember that it showed something very similar on todays 12z. Evidence from Eded (it showed a strong Greenland high) but because the image was copied then pasted, it has updated to the 18z.

I wonder if it shows something similar on the 00z, I shall watch this one closely!

Edited December 30, 2012 by Panayiotis

[kumquat]

Perturbation number 2 has caught my attention in todays runs, as you can see the 18z run for 384hrs produces this lovely Greenland high, I remember that it showed something very similar on todays 12z. Evidence http://forum.netweat...h&fromMainBar=1 but because the image was copied then pasted, it has updated to the 18z.

I wonder if it shows something similar on the 00z, I shall watch this one closely!

That would be more like it. That would be more like the snowy spells of 2009 even for our (Bristol, Cardiff) neck of the woods. There are definite signs of potential after the Azores high ridges north. Let's pump as much warm air up that way, through Svalbard if possible, as we can. Almost seeing a link-up with the Arctic high.

The model output is much more cheery even before we factor in any ssw events.

About the background teleconnections. I forget the part where we went (in the last week) from a possible stratospheric warming to an upcoming SSW???

What were the signals heralding this change?

[Panayiotis]

That would be more like it. That would be more like the snowy spells of 2009 even for our (Bristol, Cardiff) neck of the woods. There are definite signs of potential after the Azores high ridges north. Let's pump as much warm air up that way, through Svalbard if possible, as we can. Almost seeing a link-up with the Arctic high.

The model output is much more cheery even before we factor in any ssw events.

About the background teleconnections. I forget the part where we went (in the last week) from a possible stratospheric warming to an upcoming SSW???

What were the signals heralding this change?

I think Chiono said that from around mid month, we will a SSW at the start of January, but it wasn't 'set in stone' at that time, we were just looking at the stratosphere gradually warming (minor warming) but now it is looking likely that a more of a warming above 0C (which is very warm for the stratosphere, average is around -50C) is possible and this will help reverse the zonal winds, which is what a SSW essentially does, just in time for when Chiono said! Edited December 30, 2012 by Panayiotis

[kumquat]

I suppose I should get into that thread a bit more. An SSW (by it's very nature) means it's out of the blue. I guess GP and Chiono etc are basing these assumptions on external influences i.e solar radiation etc. So there's no way the models can take this into account until T=0 gets hit with some new data up in the strat.

Edit: Yep, I went reading and I was wrong! Fascinating stuff, though!

Edited December 30, 2012 by kumquat

[Panayiotis]

I suppose I should get into that thread a bit more. An SSW (by it's very nature) means it's out of the blue. I guess GP and Chiono etc are basing these assumptions on external influences i.e solar radiation etc. So there's no way the models can take this into account until T=0 gets hit with some new data up in the strat.

What I'm saying is, there's no way this can be predictable using NWP outputs at "Whatever" range.

Edit: I'm probably wrong on this and my whole assumption is wrong. I defo need to get into this stuff more. Are we saying that a SSW can be caused by global weather? I might need to go back to kindergarten!

Its a very interesting thread, my knowledge of the stratosphere isnt much and therefore I only look at the charts showing the temperature of the strat however the knowledge of the members over there, surpasses mine and I have no clue about the other things they say eg EP flux etc Edited December 30, 2012 by Panayiotis

[Panayiotis]

I suppose I should get into that thread a bit more. An SSW (by it's very nature) means it's out of the blue. I guess GP and Chiono etc are basing these assumptions on external influences i.e solar radiation etc. So there's no way the models can take this into account until T=0 gets hit with some new data up in the strat.

Edit: Yep, I went reading and I was wrong! Fascinating stuff, though!

Ha exactly the temperature on the charts go from blue to red! Probably an unintentional pun! Its called a sudden stratospheric warming because the warming can raise the temperature of the strat by +50C in a space of 5 days, that certainly is sudden! Edited December 30, 2012 by Panayiotis

[Polar Maritime]

The polar vortex is much more disturbed on this run, with the high pushing further north.

The Jet Stream heads way south, good-by Zonal..

Some nice warm air being pumped up into Greenland.

Edited December 30, 2012 by Polar Maritime

[chionomaniac]

As I am up........

The 00z is showing better extension of heights across the UK with dare I say a hint of undercutting in a weeks time. This type of evolution fits in well with a changing MJO forecast and of course the stratospheric possibilities following on from the displacement.

We may take several bites of the cherry here - it is the split following the displacement that really interests me. If we do get the secondary warming event driving in between the split, then we should see the daughter vortices weaken further and an increased likelihood of better blocking between the vortices. I am expecting to see big Greenland blocking showing up in a run in FI soon as the models fight to find the correct solution. whether that will actually occur or not is another matter. Remember the likes of Cohen and a certain GP say that it will!

[Panayiotis]

Nice looking chart on the 00z at 300hrs where does the incoming low go from here? Undercut?

I see omega high at 336hrs....

Edited December 30, 2012 by Panayiotis

[chionomaniac]

As I am up........

The 00z is showing better extension of heights across the UK with dare I say a hint of undercutting in a weeks time. This type of evolution fits in well with a changing MJO forecast and of course the stratospheric possibilities following on from the displacement.

We may take several bites of the cherry here - it is the split following the displacement that really interests me. If we do get the secondary warming event driving in between the split, then we should see the daughter vortices weaken further and an increased likelihood of better blocking between the vortices. I am expecting to see big Greenland blocking showing up in a run in FI soon as the models fight to find the correct solution. whether that will actually occur or not is another matter. Remember the likes of Cohen and a certain GP say that it will!

I didn't expect it to show quite so soon as I was typing though!!!

[Polar Maritime]

I didn't expect it to show quite so soon as I was typing though!!!

Who care's Chio ! great to see, and all in line with the stratt..

[Panayiotis]

Fi on the 00z is looking very good, check this chart out, we wait until that low moves east and it will be 2010 all over again! Remember earlier I said I would keep my eye on perturbation 2 as this was showing lovely Greenland heights near the end of the run,maybe all the members will follow this one!

Edited December 30, 2012 by Panayiotis

[Duane S.]

Fantastic FI on the GFS 00z operational, it's been coming for a while mind you. Maybe showing up a scenario that reflcts a fairly fast but more than plausable response to the warming.

The op is the pick of the bunch for a change but there are plenty of other members showing a desire to pull the Azores high to just west of, well, the Azores and this you would imagine would be a precursor to a mid Atlantic ridge of sorts thereafter.

With many members not having it yet we see some wild pressure variations over Iceland as soon as it goes lo res

Leading to...

Edited December 30, 2012 by s4lancia