Winter Model Discussion - Cold Hunting -12Z 30/12/12

[bradymk]

Another unfavourable update for cold, still we have to hope that all LRF models are barking up the wrong tree.

Not quite sure some of them take into account any SSW and as we are currently having one, its output may be unreliable. If we didnt have a SSW, i would say above average would of been correct for the rest of the winter however.

[chionomaniac]

The Beijing climate centre model updated at the end of 2012 and what it shows is temperatures above normal for the period of January to March

It also shows rain is likely to be of average amounts for England and Wales with above normal amounts for Scotland and Northern Ireland

Gavin - considering that forecast was produced on the 22/12/12, I suspect that it may not include any effects of the forthcoming SSW and therefore is not worth the pixels it is produced on.

[Summer Sun]

Gavin - considering that forecast was produced on the 22/12/12, I suspect that it may not include any effects of the forthcoming SSW and therefore is not worth the pixels it is produced on.

I did say it was updated at the end of 2012

If you want cold weather this is a great read - http://theweathercentre.blogspot.co.uk/2013/01/multiple-stratospheric-warmings-confirm.html

Edited January 3, 2013 by Gavin.

[IDO]

I did say it was updated at the end of 2012

If you want cold weather this is a great read - http://theweathercen...gs-confirm.html

...and you live in the mid-West of the USA!

[Weather Boy]

Although there are clear signs that the HLB is beginning to take shape on the GFS, I am still concerned that the PV piece over West then SW Greenland will prove poor in terms of prolonged cold for the UK:

As the above charts (t384) show, the jet is pumped up from the energy from the PV and strengthens the jetstream. Although in this frame we are influenced by a trough, this looks like it will be flattened by the jet quickly, preventing any sustained cold. That PV prevents any ridging in the west Atlantic, thus sustaining the relative westerly flow.

Things can change and will, but getting rid of that PV piece would give me greater confidence in the medium/long term potential.

Agreed to an extent, but presumably there is no reason why a Scandi high cannot deliver cold (potentially quite severe a la 1987) without the need for a Greenland high?

As Dave (TEITS) says above, it's not looking like a GH is going to be there at the outset, but it would seem to me that this is not essential for a cold outbreak, albeit probably not for any length of time from the north.

Therefore, whilst we'd like to see a GH, is there any reason why its absence should be a concern?

Edited January 3, 2013 by Weather Boy

[aitchbomb]

You seemed remarkably UNskeptical about an LRF that was produced long before the SSW that everyone knows about now.

[Paul_1978]

I did say it was updated at the end of 2012

So why did you post it then? 22nd Dec to today is TWELVE DAYS AGO - a hell of a long time in weather.

[Summer Sun]

...and you live in the mid-West of the USA!

If you look closely western Europe is mentioned

Now let's dart over to the other layers. The 5 millibar layer has a lot of things going on at once. In this case, there are actually three daughter vortices. One is located in Canada, another in western Europe, and the third vortice in Asia. They are all shown as several ovals tightened close to each other with decreasing numbers as you go toward the center of these ovals. The lowest pressure is identified with an 'L', in this case found over Canada. Also happening is a warming event, shown as the warmer colors in this image and happening over Europe and the Northeast US into the Canadian Maritimes.

[BLAST FROM THE PAST]

Posts of the models being awful again are off the mark, that is unless you want/hope/expect bitter cold to flood in within the next 3-5 days. From about 8th we see the change appearing and watch for the period 16-22. GFS has the large LP over us just centred west with northern blocking evident. Few days ago therre was nothing. Now has it got it right? Is deep FI so probably not, will we further shifting SW of the set up with the block dominating? As of now with the models....we are heading towards colder times. Chances are improved model wise, remain the same other method wise

Of course we are the UK.....and cold doesn't like us very much...

BFTP

Edited January 3, 2013 by BLAST FROM THE PAST

[latitude]

Agreed to an extent, but presumably there is no reason why a Scandi high cannot deliver cold (potentially quite severe a la 1987) without the need for a Greenland high?

Therefore, whilst we'd like to see a GH, is there any reason why it's absence should be a concern?

Just means the Atlantic can easily attack and usually wins. But who knows what could happen in the next couple of weeks.

[MR EXTREMES]

just to this is enough to tell me im getting more and more confident although detail is impossible to pin down but theres a clear trend building.

after our christmas failed easterly this time theres a much more positive trend alot better than our failed easterly and we did come close.

this time round come on weather gods bring on the ramps moaning and keep mods busy only joking.

even steve m has shown a little more optimism

[UV-RAY]

Not quite sure some of them take into account any SSW and as we are currently having one, its output may be unreliable. If we didnt have a SSW, i would say above average would of been correct for the rest of the winter however.

I'm not sure any of the LRF models take into account any SSW, hence why they are a bit hit and miss.

So why did you post it then? 22nd Dec to today is TWELVE DAYS AGO - a hell of a long time in weather.

It's a monthly update, the next one will be due at the back end of this month .

[IDO]

Agreed to an extent, but presumably there is no reason why a Scandi high cannot deliver cold (potentially quite severe a la 1987) without the need for a Greenland high?

As Dave (TEITS) says above, it's not looking like a GH is going to be there at the outset, but it would seem to me that this is not essential for a cold outbreak, albeit probably not for any length of time from the north.

Therefore, whilst we'd like to see a GH, is there any reason why it's absence should be a concern?

I just believe that the Atlantic is the current dominant pattern for the UK. With a robust GH and ridging in the west Atlantic we would close the Atlantic door and increase our chances for a sustained cold spell. A Scandi high for longevity with a westerly flow will surely be short lived and possibly be pushed east (as of December's debacle).

With the PV over W Greenland we will probably miss out on the real cold from the initial SSW effects. We then have to rely on the second warming showing on GFS (not yet ECM) to break that up. Time is therefore ticking away and obviously any cold spell will be for-shortened for the UK. And of course, once the second warming takes effect, the initial HLB from the SSW maybe reluctant to then shift to favour the UK, or alternatively shift slowly, again delaying the arrival of cold.

[Summer Sun]

So why did you post it then? 22nd Dec to today is TWELVE DAYS AGO - a hell of a long time in weather.

All of these charts only update once a month that one updates at the end of each month, the next one to update will be the Met Office probability maps some time next week

[-uksnow-]

For anyone who hasn't seen...

Matthew Hugo â€@MattHugo81

GFS ENS days 11 to 15 height anoms is impressive with major signal for high pressure to the N of the UK - http://raleighwx.americanwx.com/models/gfsensemble/00zENS11-15day500mbHeightAnomalyNH.gif …

Matthew Hugo â€@MattHugo81

00Z EC ENS are very interesting beyond 264hrs with 20 members now signalling a major -ve AO pattern with S'ly tracking lows & cold weather.

00Z GFS ENS mean for 2m temps continues to clearly show a marked progression towards colder conditions by mid-month. pic.twitter.com/D6WllN5l

then posted weatherbell AO and NAO charts however you'll have to go to his profile to see this as i cant link them across

[TEITS]

Call it hopecasting or I prefer instinct but I wouldn't be surprised if over the next 24hrs the period between +168/+192 gets upgraded. I know beyond +240 is more likely to bring a cold spell but something is telling me this could be bought forward.

Shalll post a drawing later to explain why.

[bluearmy]

i'm sure ian will correct me if i'm wrong but the way i read his last post re exeter was that despite what was showing in the nwp post day 7/10, they had very low confidence due to strat events and felt something could change at fairly short notice. of course we may need plenty of patience as is generally the case in a uk winter but the possibilities of going cold after the 12th jan were remained very much 'up in the air'.

much better jet profile to our west on the 06z gfs - should be a more blocked run

[chionomaniac]

i'm sure ian will correct me if i'm wrong but the way i read his last post re exeter was that despite what was showing in the nwp post day 7/10, they had very low confidence due to strat events and felt something could change at fairly short notice. of course we may need plenty of patience as is generally the case in a uk winter but the possibilities of going cold after the 12th jan were remained very much 'up in the air'.

much better jet profile to our west on the 06z gfs - should be a more blocked run

Yes - look at the difference in the Atlantic low - it doesn't want to move east in the reliable - could be one of those runs that gets cold quick this.

[bluearmy]

Yes - look at the difference in the Atlantic low - it doesn't want to move east in the reliable - could be one of those runs that gets cold quick this.

look north young man !!

[chionomaniac]

look north young man !!

I'm looking and liking so far

[snowking]

With the PV over W Greenland we will probably miss out on the real cold from the initial SSW effects. We then have to rely on the second warming showing on GFS (not yet ECM) to break that up. Time is therefore ticking away and obviously any cold spell will be for-shortened for the UK. And of course, once the second warming takes effect, the initial HLB from the SSW maybe reluctant to then shift to favour the UK, or alternatively shift slowly, again delaying the arrival of cold.

Hello IDO,

Just a couple of things that could do with mentioning here.

First of all with the W Greenland based PV lobe. Yep its certainly still there as the initial strat. warming episode takes place over the next week or so, however, this initial warming never particularly looked like inducing an instant tropospheric response, and so the proximity of the PV Lobe to Greenland at this stage isnt especially relevant.

What we see with this later on even on the ensemble means (bearing in mind the caveats with these that I pointed out last night) is that over time as the stratospheric PV lobe to our NW gets dragged further west away from Greenland, so does the tropospheric one:

To:

Less noticeable on the ECM mean (as it only goes to 240) but still evident:

To:

And being an ensemble mean signal thats a potentially diluted signal!

Its even easier to see on the mean anomaly charts:

To:

And further evidence offered by the NAEFS:

To:

As for the secondary warming not showing on the ECMWF, certainly not to the same extent but it is evident, albeit a little further south and less strong than the GFS suggestion:

However, as BA pointed out over on the strat thread, it may be thats its taking longer to downwell on the ECMWF, with very evident warming at 5mb:

These changes are taking place around 12-17th January, and it wouldnt be unreasonable to think we may have a further few to possibly 10 days for these to affect the UK tropospherically (which is why yesterday I suggested that Roger's thoughts of main bulk of cold arriving in February could bear fruit) but very volatile NWP at present, so I wouldnt entirely back away from TEITS's suggestions of promise showing a little sooner.

I certainly admire your caution, and you are not the only member on here being so (rightly so after the rollercoaster in early December) but there are certainly plenty of signs for optimism.

SK

Edited January 3, 2013 by snowking

[bluearmy]

there is an extra depression in the eastern states on the 06z which developed cut off from the flow. this may be helping to hold the atlantic trough back aswell so not sure how reliable the atlantic profile is on the 06z op. the arctic one is certainly of great interest as the height rise to the nw meets that coming from the other side of the NH

[TEITS]

Yes - look at the difference in the Atlantic low - it doesn't want to move east in the reliable - could be one of those runs that gets cold quick this.

Unsurprising though because in the past 12hrs we have seen a trend towards the LP not making as much progress E as originally progged and at the same time pressure increasing in the area between Greenland towards Svalbard. This trend is why we have seen an increase in sub -10C ensembles and is one of the reasons for my earlier post.

[snow drift]

Thats looking interesting.

Edited January 3, 2013 by snow drift

[chionomaniac]

there is an extra depression in the eastern states on the 06z which developed cut off from the flow. this may be helping to hold the atlantic trough back aswell so not sure how reliable the atlantic profile is on the 06z op. the arctic one is certainly of great interest as the height rise to the nw meets that coming from the other side of the NH

If the Arctic high can be squeezed through to the Atlantic sector, between the vortex troughs, then that is our preferred solution - and one that I have been hoping to see since the split was first forecast. Hints on that run.

Edited January 3, 2013 by chionomaniac