Model Output Discussion - 26Th Dec 21:25-->

[grab my graupel]

Having just read through this thread, I think it's time that some members re-read this message from Paul:

There are many instances currently whereby a small minority of members are ruining discussions by posting anti-socially (by bickering, posting incendiary or insulting comments, continually posting off topic etc), this is obviously unacceptable at any time of the year but during the Christmas and New Year period it's magnified as the team aren't online as much as they may usually be.

Due to this and to ensure that everything runs as smoothly as possible through the remainder of the holiday season, the team will be seeking to stop those causing any problems from posting onto the forums until the new year.

So, please do ensure your posts are made within the forum guidelines, and if you do see any posts which you think are an issue please hit the report button to alert the team to them.

Many Thanks

Paul

[TEITS]

Nick,Dave I take your points and I accept that a more Southerly tracking low is a more direct route to a cold spell.

However, there is the possibility of one of the biggest snow events for years across many parts of the UK with a likelihood of cold weather after the snow event. Many people would take the latter option rather than risk what could be just a frosty dry spell - particularly for inland locations.

I do agree that there is the chance of a snow event followed by a prolonged cold spell as this has been shown by the models, especially yesterday.

I suppose mate I just get nervous when looking at a possible cold spell on the models and want a risk free way of getting there.

[keithlucky]

I know reading the charts are individual ,on how you read them,but i respect rob macelwee he seem quiet positive on a very wintery 3 days.

[nick sussex]

Nick,Dave I take your points and I accept that a more Southerly tracking low is a more direct route to a cold spell.

However, there is the possibility of one of the biggest snow events for years across many parts of the UK with a likelihood of cold weather after the snow event. Many people would take the latter option rather than risk what could be just a frosty dry spell - particularly for inland locations.

Fair enough Ian, i do understand that it could be the best of both worlds, i suppose given so many previous model dramas when i used to live in the UK i always worry about the last minute variable popping up, it's a shame that the block isn't a little further east this would be another little extra insurance. I'm probably more in the get the cold first then hopefully the snow will follow camp but anyway lets hope the models upgrade the longer term potential tomorrow and deliver something that brings back fond memories of years gone by.

[TEITS]

Im going to post some charts from the NOGAPS 18Z. Now im not using the NOGAPS because I believe its correct but its a good example of what we need to see.

First of all click on the link below.

http://91.121.94.83/modeles/nogaps/run/nogaps-0-96.png?27-00

Now scroll all the way to +144 and watch that LP NE of Scotland/ W of Scandi.

Now ideally at +96 we need to see the LP further S. However if you follow that LP NE of Scotland you will see it move SW. Now ideally we need to see our LP to our S absorb the LP to our NE and eventually the whole system moves away SE.

As you can see at +144 we nearly have a monster E,ly. Now if that LP manages to get lost we would see a bitter E,ly. Now if you look at the LP to the W of the UK, if we manage to get an E,ly the LP to the W would bring a snow event to the SW and eventually undercut the block.

So in summary not only do we need to see the S,ly tracking LP as far S as possible. We also need to see the LP NE of Scotland pull away SE. If it hovers around this not only prevents us getting an E,ly it puts us at risk of milder SW,lys thanks to the LP to the W.

Hope that makes sense.

[Cecil Hogmanay Melchett]

i just watched the latest bbc forecast and they are now showing rain up to about mid wales and snow for north wales and the west midlands.i guess thats going with ecm !

[TEITS]

I saw his output earlier, so tomorrow will be either bring good news in so much as the beeb stays on track, or humble pie will be comsumed by the shovel load, because I can see no model justification for the current forecasts being diseminated. Interesting times ahead.

Having said that what might happen is the Met O back away from the heavy snow next week but then tomorrows 12Z bring the threat of snow back and this returns in the forecasts.

You seem to be suggesting that if tomorrow the BBC/Met O indicate a less wintry outlook for next week then its curtains for our cold spell. However this doesn't mean anything of the sorts. Very often due to the uncertainity of the synoptic pattern there is often wild swings between forecasts such is the unpredictable nature of our climate.

I don't know why but you seem very confident if the models are less keen on a cold spell and yet if they trend towards a cold spell your very pessimistic of them. Im curious why because surely our recent cold spell suggests these are still possible in the UK.

[swfc]

Well what a 24 hrs this has been.lol.????.Nerves shredded over the position of an area of low pressure and still know clearer. Guess its a wait and look out of the window job come next week.Either that or just stick with the fax charts. :lol:

[Michael Fishermans Friend]

Re: TEITS post - keep looking at this feature - infact yesterday (LP to the NE of Scotland) and it is typical of 'switching the tap off' for the real source of cold air, we gat these short wave features also with northerlies at high latitudes as well, quite often in our winters stopping a severe plunge of Arctic air coming directly from north to south. This time a feature trying to hinder an easterly (or north easterly). As synoptics go I think you have it spot on, if it hangs about or shifts to the north or NW then good bye to a very short cold snap, not allowing the 'buffers' of an easterly to take place.

Edited December 27, 2009 by Timmy H

[derrylynne]

Happy days -Yes but you are only talking about 70 odd miles. The charts are not set in stone - and even the day before they cannot predict the exact course of the low - or just how far the cold will be to this degree. We can only get an idea of how far south the snow will be. But - even if the rain turns to snow in North Wales and gives a dumping - that will move South and effect the whole of Wales in the output the next day. New year looks to me to be something I do not want as I want to go over a mountain to friends. My bet is for the snow to be too deep to even think about it. As said in a previous post though - I am expecting an upgrade tomorrow when the missing data is filled in....

Edited December 27, 2009 by derrylynne

[swilliam]

Just looked through the 18z and thought gosh that is terrible from a long term cold perspective -particularly this horrible looking Southerly at T192 (by the way I am I the only person that ever puts up a chart now to support their discussion - it seems a lot of people of got lazy with only one or two liners such as upgrade/downgrade LP more S/N/W/E etc. and nothing to illustrate their point).

But having had a chance to look in more detail I actually quite like this kind of evolution. It rather unrealistic to expect 2 weeks or even a month of cold across the whole of the UK - a simple look through the records will tell you this. There have only been a few occasions when this has happened. The next best thing is for the pattern to alternate between mild and cold and is probably something we should expect in most places. Next weeks event has been likened to the Dec 31 1978 event and then the 78/79 winter looked back on with fondness. My recollection of that winter (I was in Egham in Surrey) was most clearly that there were periods of cold (with some ice days) with snow - this lasted for a few days then there was a period of mild - maybe up to 2 weeks, then a renewal of the cold and more snow. So no continuous period of cold. The 18Z looks very similar to this with next weeks event, then the cold NE wind the the next LP and the Southerly (with snow at first). This is then followed by a very cold easterly (which I would like) with very low max temps and probably some nice dry powdery snow instead this marginal stuff.

This is the followed by the Scandi high sinking but still plenty of potential for further outbursts of cold. You can see the -ve AO and the split PV on the NH chart at T384 - so more to come.

So all in all this kind evolution look pretty good to me and would provide lots of interest for us as well as some major weather events.

Finally I would just like to reiterate that the battleground event next week does not look anything like the Dec 31 1978 situation as I discussed previously. It is much closer to the Jan 1982 event when there was a lot of rain in England and not much snow.

Cheers

Stewart

i just watched the latest bbc forecast and they are now showing rain up to about mid wales and snow for north wales and the west midlands.i guess thats going with ecm !

They have been showing this all day.

[kold weather]

Nick,Dave I take your points and I accept that a more Southerly tracking low is a more direct route to a cold spell.

However, there is the possibility of one of the biggest snow events for years across many parts of the UK with a likelihood of cold weather after the snow event. Many people would take the latter option rather than risk what could be just a frosty dry spell - particularly for inland locations.

The problem is Ian that cold weather may not last at all long, in which case the whole set-up is a total screw job for the south, the most likely set-up now IMO is for us to get a brief NE blast, then another attack from the SW. What then matters is just where the Greenland high go. There is good agreement on the PV slipping south. We need the upper high to slip more east then west, if it does come east then we'll keep a mean SE airflow which could become very entrenched and cold, if it slips west then its hello to the rampant jet stream and much more typical zonal conditions.

I think many people in the south would take dry and frosty over what this set-up is going to give them ,which is 2-3 days of utterly horrid weather, cold and very very wet indeed whilst northerners get snowed in...but thats just the way it goes sometimes I suppose.

Edited December 27, 2009 by kold weather

[TEITS]

Re: TEITS post - keep looking at this feature - infact yesterday (LP to the NE of Scotland) and it is typical of 'switching the tap off' for the real source of cold air, we gat these short wave features also with northerlies at high latitudes as well, quite often in our winters stopping a severe plunge of Arctic air coming directly from north to south. This time a feature trying to hinder an easterly (or north easterly). As synoptics go I think you have it spot on, if it hangs about or shifts to the north or NW then good bye to a very short cold snap, not allowing the 'buffers' of an easterly to take place.

Last post before I pop to bed.

Im going to stop being cautious and post what I think will happen.

What Tamara said earlier was spot on in my opinion. I think the models are over playing these SW and underestimating the blocking. I also believe the LP will eventually be further S. As I was saying yesterday the chances of an E,ly are now far greater than a N,ly via a Greenland HP. The link between the GH & SH is certainly appearing in the models and I reckon the blocking will eventually be further S. This might not appear straight away in the models but I think it will be the eventual outcome.

There are far more positives in the models than negatives and this is something members need to remember. We don't have a PV centred over Greenland. We have the AO which is off the scale and we have the NAO ensembles suggesting an index of -2. I have also witnessed one of the best cold spells in recent times and the lying snow I had on Xmas day was the first time in 28 yrs.

[nick sussex]

My last post of the evening, in terms of any snowfall from this low this won't be more accurately forecast until within 24 hours, sometimes even then the models are not going to get this totally accurate with still some leeway likely, the areas on the periphery roughly 50 miles either to the north and south of the main risk area are going to need to be patient, these areas will probably have to resort to nowcasting. By tomorrow the ukmo will be able to start bringing their MOGREPS 48hrs ensemble forecast into the mix as this will then be able to tune up the smaller scale detail for the start of the possible snow. The very latest normal 48hrs ukmo model 18hrs run looks a little better in terms of the trajectory of the low to the sw and also a slightly stronger ridge thrown down from Greenland, every little detail or trend counts at this stage seeing as the start of the possible snow is within 72 hrs.

Anyway have a good night all, let's hope for some good model runs tomorrow.

Edited December 27, 2009 by nick sussex

[rmc1987]

Looking at this it would appear that it's rain for my area. More often than not it has looked like that. Whilst it snows further North much to my dismay but I should be used to that by now. I'd hope atleast it will at some point it'll turn to snow but that'll just make it slushy muck! Can anyone verify this? I'm guessing I'd really need the low further South to benefit?

[phil nw.]

My last post of the evening, in terms of any snowfall from this low this won't be more accurately forecast until within 24 hours, sometimes even then the models are not going to get this totally accurate with still some leeway likely, the areas on the periphery to the north and south of the main risk area are going to need to be patient, these areas will probably have to resort to nowcasting. By tomorrow the ukmo will be able to start bringing their MOGREPS 48hrs ensemble forecast into the mix as this will then be able to tune up the smaller scale detail for the start of the possible snow. The very latest normal 48hrs ukmo model 18hrs run looks a little better in terms of the trajectory of the low to the sw and also a slightly stronger ridge thrown down from Greenland, every little detail or trend counts at this stage.

Anyway have a good night all, let's hope for some good model runs tomorrow.

Good post nick,

Looking at all the output today in spite of the variables regarding the snowline across the uk i believe the overall pattern is solid for cold to develope across the UK by the end of the week.

The overall pattern is still good for cold,

http://www.meteociel...&mode=0&carte=1

http://www.meteociel...&mode=0&carte=1

http://www.meteociel...h=96&carte=1021

An area north of the front is gonna get a lot of snow which will move south in time,

l

After that well let`s wait and see,as i am happy to stick with the fax for now.

Edited December 27, 2009 by phil n.warks.

[SMU]

Evening ALL-

Its difficult to know where to begin tonight, so many posts, so much model evaluation-

I suppose seeing as nearly all the models have a grip on the 'type' of track the low is going to take then there isnt much point of disucssing it- other than to say that I still think the trough will elongate along the channel perhaps giving a better profile of colder air to the central & possibly southern portions of the UK-

Its also pointless to post up maps for snow as the track/ elongation of the trough has a direct impact on the PPN distribution- however the marker laid out of Central wales has been pretty rigid from the start & again I cite that this area could be the hardest hit- especially at some minor elevation-

The subsequent evolution then becomes almost tantalising for everyone because if the 'proper'cold is unleashed from the East then that will certainly keep everyone happy-

We do have a problem though - as this surge from the East that I highighted the potential for last night has a rather annoying posive tilted shortwave sitting in the flow over southern Norway-

here it is firmly in the way on the GFS at 150-

http://91.121.94.83/modeles/gfs/run/gfsnh-0-150.png?18

now, no amount of willing from the residents of NW are going to force it South east- it needs to get pushed that way-

Also VERY VERY important here is the fact that when the Siberian/ artic high starts ridging west we do NOT have an infinite timeline to delivery the Easterlies-

We have a window of about 24/36 Hours tops- After this the block that origially started moving wsw piles up on the Eastern flank of the shortwave - the westerly vector then just loses its momentum & things start to head south ( yep you guessed it- towards central Southern Europe)

WHo remembers this- the huge failed easterly-

http://www.wetterzentrale.de/archive/ra/2007/Rrea00120070220.gif

See the positive shortwave over Norway it will not just turn over & face the right way- the southern arm of the jet is moving NE from iberia-

Now look at this example-

http://www.wetterzentrale.de/archive/ra/1987/Rrea00119870110.gif

The jet flow is moving SE through the UK over france - which on turn rotates the shortwave the way we want it- with the northern flank moving back to face ne> Sw NOT AS WE SAW IN 2007 SE>NW.

Its going to be VERY hard to get an Epic easterly from this ( after the initial set up)

the shortwave moving into the SW approaches at around 162 is coming in at EXACTLY the angle we dont want it- because its NE quadrant is acting against the force of the siberian high moving SW-

Ian browns favourite this one- although another epic fail-

http://www.wetterzentrale.de/archive/ra/2001/Rrea00120010203.gif

looks great but the southerly jet moving NE kills the flow stone dead ( even though shetland did well out of it)

http://www.wetterzentrale.de/archive/ra/2001/Rrea00120010204.gif

TO Deliver an easterly we need a flow around t160- that goes either miles & miles further south so a shortwave undercuts the trough over Scandi & supports the cold moving west or the Iberian ridge is much further west & actually that shortwave heads up still NE but it goes towards iceland- as the jet will loop up then back SE like we want it-

In all reality whilst it looks great the killer may well be the southern arm moving North over the atlantic which would again be typical of the UK's luck- with the motto if anything can go wrong it will- even with a cut off greenland high thats now modelled as being slightly more west based & not an iceland block.....

in Summary- plenty available to keep up on our toes especially between 42-96, thereafter a slight lull- but good consensus in modelling of a NE flow, then the probability of the jet sweeping it away to leave us at best with SE winds-

Best chance of sustained cold from the East is if the upper trough gets undercut as it will force it west ( GFS ens PTB 13)

cheers

Steve

Edited December 27, 2009 by Steve Murr

[AtlanticFlamethrower]

The charts look like synoptic spagetti to me. Has something like what is shown here ever happened before?

Triplet low, another to the right of that below a messy Greenland - Siberian high link up

I don't think the models have yet got a consistent realistic evolution for the next couple of weeks.

I think after something like T120 here we will get the Siberian high pushing down lower over Scandinavia blasting France and UK hard

[phil nw.]

Evening ALL-

Its difficult to know where to begin tonight, so many posts, so much model evaluation-

cheers

Steve

A good analyisis Steve,

However i think too many posters have been doing mental gymanstics over the last day or so.

Simply put we have a Southerly jet and northerly blocking and the UK on the Eastern edge of an omega block,here,

http://www.meteociel.fr/modeles/ecmwf.php?ech=120&mode=1&map=1

We are going to have trough disruption from the Scandi trough and the minor details will change from run to run.

The overall pattern is good for cold and going forward,maybe the south will experience some less cold excursions, but it`s a damn sight better than we are normallly used too.

[BLAST FROM THE PAST]

My opinion is RAIN for south of M4 for sure but big cold event following....the SW IMO is being overplayed.

BFTP

[Craigers]

Last post before I pop to bed.

Im going to stop being cautious and post what I think will happen.

What Tamara said earlier was spot on in my opinion. I think the models are over playing these SW and underestimating the blocking. I also believe the LP will eventually be further S. As I was saying yesterday the chances of an E,ly are now far greater than a N,ly via a Greenland HP. The link between the GH & SH is certainly appearing in the models and I reckon the blocking will eventually be further S. This might not appear straight away in the models but I think it will be the eventual outcome.

There are far more positives in the models than negatives and this is something members need to remember. We don't have a PV centred over Greenland. We have the AO which is off the scale and we have the NAO ensembles suggesting an index of -2. I have also witnessed one of the best cold spells in recent times and the lying snow I had on Xmas day was the first time in 28 yrs.

ive been following your posts for the past 5 years and you always have been right with these setups! I totally understand what you mean with the current jigsaw pieces and the most usual outcome! you can say this winter is different with what has happend and my self cant see the usual SWerlies coming back!.

[Mikel Nimbus]

The charts look like synoptic spagetti to me. Has something like what is shown here ever happened before?

Triplet low, another to the right of that below a messy Greenland - Siberian high link up

I don't think the models have yet got a consistent realistic evolution for the next couple of weeks.

I think after something like T120 here we will get the Siberian high pushing down lower over Scandinavia blasting France and UK hard

I'm not completely convinced with what has been said on here lately, regarding the lack of data over Christmas affecting the chart outputs, but something does seem to be slightly amiss. I'm not a synoptics expert, but over the last few days we have seen some strange and inconsistent setups. One GFS run saw a Scandi High shoot SE across the continent at speeds I've never seen before.

When the charts settle down we should get an idea of what northerly blocking setup will prevail. My money is on the Greenland high sticking around due to the placing of the split PV.

Edited December 27, 2009 by Mikel Nimbus

[tumbleweed]

I only come and read the posting on this forum site during the winter as I am a real snow fan.......I remember the winters of '79, 81 and they were fab.

Now scratching my pine cones....I just have a feeling next week is going to be special, I am content the snow will fall, Eurostar will fail again and general national chaos....it is one in the eye for the global warming tree huggers.

I am enjoying the forum posts on here of: "it's going to be a big snow event".....6 hours on "It's been downgraded"...."now it's back on"....none of that matters to me as I feel with my experience of winters during the 70's, 80's and 90's that this is going to happen.

Putting my cards on the table...it will get cold Tuesday, snow on Wednesday and blizzards on New Year's eve with cumulative snow totals of 5 - 10 inches across the three days for most of the country.

We have stocked up on drink, tins and have plenty of chocolate in the house, plus torches and candles.. let the lamp post watching commence.

Be prepared for the greatness coming

Edited December 27, 2009 by tumbleweed

[kumquat]

Loving all the fascinating output at the moment - and thanks to all the seasoned veterans and all others for their input. Anyway can we clear up the SW = SouthWest and SW=ShortWave stuff. The SW acronym is sometimes making me pull my hair out (and many others, I'd suggest!)

Merry Christmas to all.

[swfc]

Wel out to 120 hrs and yet again the short wave holds up the easterly flow.its into scan but not sure if the low can slip sse. :rolleyes:wow so so close at150 hrs,but.?

Edited December 27, 2009 by swfc