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phil nw.

Winter Model Discussion - Cold Hunting -12Z 06/01/13

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A new thread to continue discussions then and in readiness for the 12Z outputs.

It`s certainly building up for a change to a colder setup later this week as pressure rises towards the north with a cold block forming across the UK by the weekend.

post-2026-0-44528600-1357478273_thumb.gipost-2026-0-62945500-1357478337_thumb.gi

as this establishes we start pick up a feed of colder air from the east as a trough drops down through Scandinavia.Details of the surface features still to be determined at this stage but if we look at the 850hPa mean charts for Sunday next from the last GFS/ECM runs we can see the modelling of the colder across the UK by then.

post-2026-0-43028100-1357478597_thumb.pnpost-2026-0-45020600-1357478610_thumb.pn

In spite of some ups and downs -particularly with the last few GFS operational runs- mean 500hPa Heights are still strongly signalling this cold pattern to establish -much in line with the latest phase 7 MJO forecasts.

MJO post-2026-0-96277900-1357478783_thumb.gi

post-2026-0-31103800-1357478802_thumb.gipost-2026-0-75579600-1357478811_thumb.gi

Falling heights over Europe and a solid block around S.Greenland/Iceland is still favoured by the both Ens outputs.

One final chart

post-2026-0-27663200-1357479031_thumb.gi

showing NA ens outputs for 00z run going into a negative AO-and notice the GFS operational going positive in the midrange against the trend from the Ens.members.

Ok then so all still looking positive for cold lovers so lets have good discussions based around the outputs and keep it friendly please.

Thanks all.

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To take my reply to IanB a bit further at the end of the previous thread, this T72 strat image shows beautifully why we have a much better signal for high lat blocking to be maintained:

gfsnh-10-72.png?6

Warming areas to our NW and NE and a segment of vortex isolated to our south helping to sustain some lower pressure to our south. The main vortex segment is forecast to move further to the east, surely a signal for retrogression. 2 days on and we have this shape to the strat, with a clear signature for sustained high lat blocking:

gfsnh-10-120.png?6

I think this is very strong evidence that we are going to get some lovely wintry synoptics in the medium term. Tomorrow's adjusted CPC anomaly charts will be the final piece of evidence I am looking for...

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Just looking at the mean, we are expected to see the cold starting on the 12th and then nearing average temperatures on the 18th so that's a 6 day cold spell, thats just the mean so maybe even colder solutions but as I say this the same can be said the same for the warmer solutions but so far its looking very good IMO!

For Cardiff:

post-17320-0-39775200-1357480545_thumb.g

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I must say the ECM Ensembles for London are very impressive with a continued drop in temperature right up until the end of the forecast period and better than any set we had during December (for London anyway). Very few members milder members longer term. However the uncertainty continues and I would like to see more agreement between ECM and GFS before I get too excited but for now I am happy that the ECM ens are now very good whereas they weren't only a few days ago. The outlook is one of huge potential but to be remain cautious still, next couple of days very important for seeing where we go with this but the 500mb anomaly charts have been consistent with this for a few days now.

post-16336-0-48270400-1357481568_thumb.g

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So its SSW day, the day we begin to see with more clarity what true effects it will have on the trophosphere. ECM last two outputs have been fantastic, need more of the same this evening please, need the ECM to be a consistent parent to the GFS.

On to the 12z's, promises to be an enthralling evening. Got the cup draw this afternoon also, look out for ball number 2!

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I wonder if the online record for the forum will be smashed in the next 48hrs or so

C.S

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Catcol - careful using the meteociel strat temp charts. They do not show where the heights are situated. Dont assume coldest area = lowest heights.

Aso, i keep reading that the models dont have the strat warming in the starting data as yet so are not taking account of it. Not true, the models are creatng the forecast of the ssw in the same 3D atmospheric simulation which generates the trop run we look at. As we get closer to the warming, one would hope the models will deal better with the complex dynamics in the strat which will dictate how quickly the warming is able to propogate. I wonder how many layers in the strat mogreps has? ecm op has more horizontal layers than the other models so, in theory, should deal with this better. Will it though?

So where are we? Well, i rather doubt its too clever looking much further than the back end of the week. Next weekend looks pretty compex at the moment. It wasnt too many days ago that no model was taking any energy under the blocking. now we are sure that energy will undercut. i would be waiting to see the main models firm up on this at day 5. That means waiting for tomorrows 12z runs. Sorry.

What happens to the blocking thereafter can almost be looked at seperately from the weekends events. we have a very solid looking ecm op and mean re greeny ridge and gfs/gefs has come some way towards it today. However, the renewed energy coming into the atlantic on gefs which began to show on yesterdays 06z suite cant be ignored. its another waiting game. Given the apparent quick response of the trop to the initial warming and drop in zonal flow, i would be cautious about the output for week 2 at the moment as it may again be prone to revision as renewed wave activity in the strat could well have repurcussions in any direction. the favoured outlook would be more slowing of the flow and possible drift sw of the vortex to our ne if the flow is being over stated by the models as they did with the upcoming period. It remains absolutely fascinating and its a shame we didnt get a dump in dec as i suspect watching it evolve would be less stressful if we had.

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For those who may have missed my post in the old thread I'll copy it in here

The current take on next weekend

Untitled_zps22f1db47.png

It should be noted that Chris expressed the uncertainty in this for the end of the week so anyone who gets there hopes up to much could be sadly disappointed

Here is the forecast its self

Some promising signs for colder weather

Way out in FI but 24 hours of snow for some!

prectypeuktopo.png

prectypeuktopo.png

prectypeuktopo.png

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I'm fascinated with this quite sudden change to cold, especially as last week it looked like zonal for a few more weeks. Just shows how FI charts are really just for interest. Hoping for cold/lots of snow but am not getting excited until t24....if it gets that close ;)

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I'm fascinated with this quite sudden change to cold, especially as last week it looked like zonal for a few more weeks. Just shows how FI charts are really just for interest. Hoping for cold/lots of snow but am not getting excited until t24....if it gets that close tease.gif

Yes and there is only one word for the sudden change, a SSW!! Amazing how it can completely change a hemispheric pattern, I have limited knowledge of the stratosphere especially compared to my "knowledgable" field however it has been the most interesting topic for me the last few winters by far and looks like determining the rest of the winter. I always thought one of the big factors for this winter was SST anomalies which is my expertise, especially around Greenland and the North Atlantic where there was a "classic" tripole showing but looking now, I am not sure whether this is as big of a factor as i first thought. NH Snow cover for me has been one of them, huge rapid growth in October was important. Sorry not really model related, got ahead of myself.

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"...and its a shame we didnt get a dump in dec as i suspect watching it evolve would be less stressful if we had."

I just want to say that I have been watching this forum for many years now and you guys/girls totally rock. I have learnt so much! Not enough to actually comment on the models but felt I wanted to be brave enough to comment here to commend you all for contributing to this highly addictive forum. Its because of you that I now know so much about the warming in the stratosphere, the PV and it's affects on our Island and surrounding areas. This for me is a triumph in itself.

Blue Army, you are right about this stress, it would've been less stressful but my oh my what a fascinating model watching (or forum watching in my case) that period was! Even though 'That ECM' failed, in my eyes I was still happy for that awesome stress! It has made this winter (my favourite forum watching period) rule over previous ones - even 2010.

Anyway, this was just a thanks really - you have all given me quite possible hundreds of hours of viewing pleasure! No doubt you have seen me stalking and liking comments. And I am dead excited about the current output and developments way up high in the strat.

Thanks again for sharing all your knowledge.

Alpine Glow.

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Well a pretty big set of 12zs coming up. I expect the GFS to remain messy for the end of the week but maintains it's consistency with regard to the Greenland area. I would expect the ECM to follow in lowering heights in that region from days 7-10.

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Well a pretty big set of 12zs coming up. I expect the GFS to remain messy for the end of the week but maintains it's consistency with regard to the Greenland area. I would expect the ECM to follow in lowering heights in that region from days 7-10.

Why?

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Well a pretty big set of 12zs coming up. I expect the GFS to remain messy for the end of the week but maintains it's consistency with regard to the Greenland area. I would expect the ECM to follow in lowering heights in that region from days 7-10.

Yep the ECM take on things could be very interesting tonight, will it stick with its outlook?

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Well a pretty big set of 12zs coming up. I expect the GFS to remain messy for the end of the week but maintains it's consistency with regard to the Greenland area. I would expect the ECM to follow in lowering heights in that region from days 7-10.

I'll be surprised if it does - It'd be against all the Stratospheric & MJO signals, if anything I'm expecting the GFS to continue to upgrade the heights across Greenland as it has been doing gradually in the last few runs.

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Well a pretty big set of 12zs coming up. I expect the GFS to remain messy for the end of the week but maintains it's consistency with regard to the Greenland area. I would expect the ECM to follow in lowering heights in that region from days 7-10.

In normal circumstances I would agree, but with the effects of a SSW impacting the outlook, that's a very premature and bold claim.

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Well a pretty big set of 12zs coming up. I expect the GFS to remain messy for the end of the week but maintains it's consistency with regard to the Greenland area. I would expect the ECM to follow in lowering heights in that region from days 7-10.

I disagree Ian. The 12z's are not 'big'- they will be different again for the 00zs and no matter what the 00z suite does, the 12z tomorrow will be 'big'.

Expect many big differences and erratic modelling. Stratospheric modelling shifts the polar high into Greenland whilst maintaining a weak vortex over Hudson Bay and Scandinavia. We'll work from that.

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Shame to a small extent the models have backed away from dropping the PV from the Arctic into Scandinavia but fortunately the cold air does still make us given the any easterly flow will be strong enough.

Would be nice too see if the UKMO trends towards the GFS/ECM in having a stronger Scandi high developing, it seems this model is the least reluctant to showing easterly winds unlike in the December period where it was consistent in showing this but got it wrong.

Be interesting what the 12Z runs show, I won't be too disheartened if the ECM backs away from its heights into Greenland as that is FI anyways.

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In normal circumstances I would agree, but with the effects of a SSW impacting the outlook, that's a very premature and bold claim.

The ECM have strong heights near Greenland by D10: post-14819-0-56871700-1357485871_thumb.p

It is therefore more than likely that these will be downgraded than upgraded. MOGREPS are apparently (according to a Twoweather post) also showing lower heights in Greenland, and they are about 50/50 at the moment that we have a sustained cold spell or it breaks down (probably only temporarily) after the transitional easterly.

It seems likely (IMO) that the two models will edge closer to each other.

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@Ian and everyone else

Well a pretty big set of 12zs coming up. I expect the GFS to remain messy for the end of the week but maintains it's consistency with regard to the Greenland area. I would expect the ECM to follow in lowering heights in that region from days 7-10.

He is thinking it cant get any better? I hope he is wrong though, if he gave some evidence for his reasons i might back him up but so far no one knows.

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Well a pretty big set of 12zs coming up. I expect the GFS to remain messy for the end of the week but maintains it's consistency with regard to the Greenland area. I would expect the ECM to follow in lowering heights in that region from days 7-10.

Bold claim as usual Ian. Why don't you put some flesh on the bones and provide some evidence for your assertion? In some ways I respect the sheer persistence of your mild bias but without any evidence it is the same old rubbish.

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He is thinking it cant get any better? I hope he is wrong though, if he gave some evidence i might back him up but so far no one knows.

The models are good enough! Of course things won't stay that way forever but for those claiming it woud be mild throughout the winter they will now have more of a challenge calling an end to this cold period, but we all already know things will get mild in spring anyway!

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@Ian and everyone else

He is thinking it cant get any better? I hope he is wrong though, if he gave some evidence i might back him up but so far no one knows.

I just hate it when people make such bold statements without backing up there post with any evidence or reasoning. Otherwise the poster will not be taken seriously :)

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