Model Output Discussion - 28th November - 4th December

[chionomaniac]

The ECM op is milder than the GFS, I'm willing to bet any money on that out to 240hrs, the ECM is a classic looking chart but isn't quite there. The GFs looks 'boring' but I'm willing to bet you'd get a signifcant inversion in such a set-up and probably fog/freezing fog with it.

As others have said there really isn;t any support for the ECM op run, I'd feel confident that 7-8 times out of 10 the ECM solutuion will lead to a cold shot for Europe but we'd be just too far west probably with fronts straddling the country. We'd need probably a strong low to cut-off at 240hrs and its next to impossible to tell what would happen next. Most of the time a new LP will form its just whether it can cut-off or whether the PV swings it round to the north. Tough call!

Remember when I say cold with the GFS...its inversion cold...which would be highly likely given the time of year and the set-up before it.

Overall though there is nothing really to moan about in the models today, I think things are setting up rather nicely considering the near record AO values we have had in the last few days...and I think the ECM is a BIG hint for what will happen deeper into winter, just think right now is too soon...

Yes, an exact opposite with the record negative values of the NAO last year.

I have read that the AO has been greater than +5SD's 14 times since 1950. As I can't access the data for some reason - I think my new router blocks it - can anyone see how many times this has happened in December and which Decembers? What was the Jan's and Feb's AO values if it did?

http://www.esrl.noaa.gov/psd/data/correlation/ao.data

[kold weather]

I think Chionmaniac more often then not we get a strong block at some point in Jan/Feb, tends to be a 30-45 day lag from the peak of the +ve AO from what I've noticed and judging from other comments I've seen on other forums (americanwx which I know you are on)

High is a little further north on this run, would probably buy us another day of inversion cold if it came off...but equally probably a lower chance of that inversion happening on this run judging from the high's position!

[shedhead]

Hi Kold - with the AO potentially yet to peak, even given the middle of your spread, we eat up a fair portion of, if not all of January. Not ideal for those looking for proper cold in the short or even medium term, but it does

dovetail quite nicely with GP's Winter forecast which suggest 'patience' is and will remain the watchword.

Edited December 4, 2011 by shedhead

[phil nw.]

Just continuing T240 speculation re,the Azores High.

My view is usually from a cooler Zonal pattern with an active vortex we at some point evolve towards a milder SW flow as those Hts to the South ridge in.

GFS has the likely scenario,based on current output but i would bet a milder flow wouldn`t establish too long.

The tendency of the jet buckling and moving South again seems to be a repeating factor and we could still evolve into either a rerun of PM North Westerlys or see ridging of heights towards Scandi.-which is something that the models keep hinting at.

Edited December 4, 2011 by phil n.warks.

[BLAST FROM THE PAST]

Just continuing T240 speculation re,the Azores High.

My view is usually from a cooler Zonal pattern with an active vortex we at some point evolve towards a milder SW flow as those Hts to the South ridge in.

GFS has the likely scenario,based on current output but i would bet a milder flow wouldn`t establish too long.

The tendency of the jet buckling and moving South again seems to be a repeating factor and we could still evolve into either a rerun of PM North Westerlys or see ridging of heights towards Scandi.-which is something that the models keep hinting at.

Yes, that is a route to cold seen many times in the past and 06z T384 shows that nicely. [T384 used as an example not that the run is right]

BFTP

[Duane S.]

Yes, an exact opposite with the record negative values of the NAO last year.

I have read that the AO has been greater than +5SD's 14 times since 1950. As I can't access the data for some reason - I think my new router blocks it - can anyone see how many times this has happened in December and which Decembers? What was the Jan's and Feb's AO values if it did?

http://www.esrl.noaa...elation/ao.data

The link doesn't work for me either but I would have thought it would possibly be

2006/07, Jan sayed stayed high then went neg in Feb.

1992/93, Jan very high then dropped to neutral in Feb.

1991/92, both Jan and Feb +ve months.

And of course 1988/89, after a strong Dec both Jan and Feb values went through the roof.

Worrying as unless we see quite a distinct drop off of the AO in the coming weeks, December could record the highest +AO December average on record, quite incredible after witnessing the extreme lows of the past two years!

[sebastiaan1973]

Yes, an exact opposite with the record negative values of the NAO last year.

I have read that the AO has been greater than +5SD's 14 times since 1950. As I can't access the data for some reason - I think my new router blocks it - can anyone see how many times this has happened in December and which Decembers? What was the Jan's and Feb's AO values if it did?

http://www.esrl.noaa...elation/ao.data

chio, these are monthly data, in stead of daily, so I can't help you.

[nick sussex]

A couple of GEFS ensemble members going for a low cutting se'wards now with a build of pressure from the ne as the low tracks into Europe, eventually the ridge is edged south into the Continent.

Because of those uncertainties upstream it's hard to place alot of faith in any of the operational output within 168hrs,however high pressure nearby to the UK does seem likely though but its really what the exact evolution is to bring that in.

You'd have to put the GFS/UKMO as the current most likeliest outcomes in terms of how you get to that point,all will be revealed eventually!

[Glacier Point]

Yes, an exact opposite with the record negative values of the NAO last year.

I have read that the AO has been greater than +5SD's 14 times since 1950. As I can't access the data for some reason - I think my new router blocks it - can anyone see how many times this has happened in December and which Decembers? What was the Jan's and Feb's AO values if it did?

http://www.esrl.noaa...elation/ao.data

Keep hitting F5, I get the same problem. Eventually they load.

Worth noting that there is a subtle disconnect between the AO and NAO domains in December (but in January and Feb they are much more strongly correlated). It's interesting with the lagged association of bocking following a strong vortex event. Yet another line of analysis which suggests blocking at high latitudes later rather than sooner.

In the meantime, solid ensemble support for a mean ridge close to the UK for week 2-3 of December.

[iceaxe]

well what a suprise a downgrade for fridays cold snap this morning.i posted that it would happen yesterday.people need to not just use models but also use data from past similar set ups that is the only way you will ever make good predictions.i think the meto are way off the mark at the momment.

[nick sussex]

I'd put the following in order of most likely given all the output:

1. The GFS looks on past experience the most likely with PV to the north, Euro high, driest in the south and east, chances of some colder conditions in those areas.

2. The UKMO suggestion, the high toppling towards Scandi, a briefish east/ne flow before the ridge settles further south, probably a better chance of some surface cold.

3. Any ridging gets flattened quickly, a mobile pattern but temps recovering to average in the north and mild in the south.

4. The ECM, low cuts se'wards, high pressure develops to the east but unable to force enough trough disruption, UK is the battle ground and all the cold stays in eastern Europe.

5. The same as above but with the pattern further west, much colder conditions from the east.

6. Proper Greenland block, no chance within the next two weeks.

Edited December 4, 2011 by nick sussex

[Frosty.]

Keep hitting F5, I get the same problem. Eventually they load. Worth noting that there is a subtle disconnect between the AO and NAO domains in December (but in January and Feb they are much more strongly correlated). It's interesting with the lagged association of bocking following a strong vortex event. Yet another line of analysis which suggests blocking at high latitudes later rather than sooner. In the meantime, solid ensemble support for a mean ridge close to the UK for week 2-3 of December.

The models are being very mean, all us coldies want is a proper cold snap but the best chance of this appears to be in the next 5 days before we begin to reset to the dross we have had through november.

[johnholmes]

well what a suprise a downgrade for fridays cold snap this morning.i posted that it would happen yesterday.people need to not just use models but also use data from past similar set ups that is the only way you will ever make good predictions.i think the meto are way off the mark at the momment.

I think you are on a wind up-folk not agreeing with me simply look at the 00z and 06z ouputs from GFS and the other models.

As to your comment about past similar set ups I did try to explain to you yesterday how the models work, with admin/mods leaving it in the thread even though it was off topic really-did you read it?

[Duane S.]

The Euro high scenario has been my form horse for a while now and to be honest I struggle to see it not happening in one guise or another. Plus we may well have to live with it again for a fair chunk of December but I really do expect the models in the coming days/weeks to start showing in FI more of a robust block to the NE edging westwards towards us, forget a Greenland block for now, this is our optimistic hope heading into the start of 2012. Not withstanding of course that Scotland, the far North and high elevations could well have wintery spells through December but for now the South in general is going to have to wait a while for anything decent.

[ukpaul]

Looked at GFS 06z and the ECM 00z and couldn't see any reason why people would say it downgraded cold, thought they must mean the GFS 00z and looked at that but, also, no downgrade.

Maybe some look at the high and don't realise the consequences in December of having that over us or maybe they are just deliberately trying to wind others up.

Edited December 4, 2011 by ukpaul

[clark3r]

Not good for the very dry south if the gfs predicting correct looks like after this week could be very dry for couple of weeks!

[Uncle_Barty]

Yes, an exact opposite with the record negative values of the NAO last year. I have read that the AO has been greater than +5SD's 14 times since 1950. As I can't access the data for some reason - I think my new router blocks it - can anyone see how many times this has happened in December and which Decembers? What was the Jan's and Feb's AO values if it did? http://www.esrl.noaa.gov/psd/data/correlation/ao.data

C - have you tried using a web proxy to get to the site?

Looking at the 06z ensembles, high pressure building down here seems to be the form horse, supported by most members by this time next week.

[nick sussex]

The UKMO further outlook for 6-10 days discounts the ECM 00hrs output and goes with the UKMO/GFS.

If that is the way forward then it's hard to judge at this timeframe where exactly the Euro high will set up, for surface cold you really need this centred to the east or se of the UK to avoid an Atlantic influence in the flow.

Quite a few years ago we did see quite an extreme inversion with the high centred right over the UK but generally you need the high centred in a location to draw in a se or easterly flow, in these set ups theres often a marked north/south split across the UK.

In terms of any northerly this looks brief in terms of potential to deliver snowfall, much depends on how far north the ridge gets initially and also the manner in which it topples.

We should hopefully see the models come to agreement this evening as we are talking about large differences within the normally reliable timeframe.

[chionomaniac]

Keep hitting F5, I get the same problem. Eventually they load.

I am on a mac and have terrible trouble loading all esrl/cpc sites presently. They are sporadic at best. However on IE windows at work they are fine . Strange.

[stewfox]

If we look closely at the latest 500mb anomaly chart outputs it is possible to make a case out for either the T+240 GFS or ECMWF charts.

But the main form horse must be on pressure rises, at that time scale, say out to T+3 days or so later, occurring to the SW of the country, so more settled anticylconic type weather edging in from the SW. How much fog and frost there would be is of course entirely dependent on cloud cover and that is impossible to say this far out. Again the betting would be INITIALLY, given where the ridge would originate from, a fair amount.

What happens beyond that can be no more than speculation NOT forecasting in my view.

Are you suggesting FI is T72 at present ?

My understanding

ECM offers a cold shot but too far west but depends where the low heads ?

GFS if it varifies ,significant inversion with perhaps freezing fog ?

I need to read up more on short waves

[kold weather]

I think in terms of getting cold, the 06z GFS is probably the best chance at getting 'sustained' cold right now even if it isn't every body's cup of tea.

Still it'd probably be cold enough to at least give an average/cool CET despite the early fears about this December being a mildfest...if we were to pull off an SSW then chances are good that'd we would end up having a below average winter..

Anyway for now Friday's cold shot looks brief, probably not much in the way of showers away from coastal areas, will almost certainly be cold enough for snow however.

[johnholmes]

Are you suggesting FI is T72 at present ?

My understanding

ECM offers a cold shot but too far west but depends where the low heads ?

GFS if it varifies ,significant inversion with perhaps freezing fog ?

I need to read up more on short waves

The T+3 days refers to post T+240!

short waves is a term I find used too often

Edited December 4, 2011 by johnholmes

[chionomaniac]

C - have you tried using a web proxy to get to the site?

Looking at the 06z ensembles, high pressure building down here seems to be the form horse, supported by most members by this time next week.

I have never heard of a web proxy before Jim and missed your post this morning. But thanks it has reopened all those sites again.

Now I can see that the GFS 100 Hpa T+240 chart is suggesting Scandi height rises.

[kold weather]

Its interesting, the broad picture was suggestive of a Euro high but it looks like the P{V might pull just far enough west to allow the HP to build close to the UK. It makes a big difference to the practical outcome of the weather.

Will have to wait and see how that evolves, but a HP close to the UK, maybe just centered to the east/south-east of the UK is IMO the most likely solution now.

[Partholon]

Its interesting, the broad picture was suggestive of a Euro high but it looks like the P{V might pull just far enough west to allow the HP to build close to the UK. It makes a big difference to the practical outcome of the weather.

Will have to wait and see how that evolves, but a HP close to the UK, maybe just centered to the east/south-east of the UK is IMO the most likely solution now.

Do you think it will eventually move towards Scandinavia or sink...?

Edited December 4, 2011 by Partholon