Model Output Discussion - 16th Jan 12z onwards - Smile While You Post!

[The Enforcer]

It's a more complex situation, on Wednesday for example there are times where snow looks possible at low elevations down south but others where it doesn't. Looking at the EURO4 would give you a clearer view but only from 48 hours before.

Don't make the mistake of thinking there will be no snow down south. I suspect most will see a bit fall from the skies, just not what we would all hope for.

I'd be surprised if a little snow doesn't fall in most places at some point.

Warm sector will get stronger the further south you go, so surface temps, 850s and dew points get more unfavourable the further south you go. These are negated a bit the further east you go, but then this positive is cancelled out by the fact the ppn begins to fragment as it enters the southeast. Wednesday however there is some potential for snow in the southeast, but too far out to say at the moment.

Thanks for the replies. I guess I'm really trying to understand what the cut-off points are for where the 850/dew point/wet bulb values cease to be favourable. As pointed out by UKPaul above, the complexity means that it's almost a case of waiting until the last set of runs come out before the event to see what might emerge. I always think that the NMM modelling looks more realistic than the Euro 4, unfortunately, the only link I have for the former is centred on France and just gives a partial view of the UK.

Edited January 17, 2015 by The Enforcer

[Met4Cast]

Maybe but that doesn't fit with the trend in these ensembles going the other way as we are nearer the time does it?

Choosing one ensemble member to predict the weather 6 days away when the high resolution models cannot even agree on the next 12 hours isn't really the way to go.. 

 

Ensembles as a whole show the cold hanging on, todays trend has been for Westward corrections. I'd say at the moment, the trend is for perhaps a day or two of cold before North-Westerlies/Westerlies arrive.

 

If we continue to see trending Westwards tomorrow we could very well end up with the Scandi High keeping the Atlantic at bay allowing more undercutting and a prolonged cold spell. As I said above though, little support for this currently but todays models give some slight hope for this, whereas yesterday there wasn't any.

[Mucka]

Choosing one ensemble member to predict the weather 6 days away when the high resolution models cannot even agree on the next 12 hours isn't really the way to go.. 

 

Ensembles as a whole show the cold hanging on, todays trend has been for Westward corrections. I'd say at the moment, the trend is for perhaps a day or two of cold before North-Westerlies/Westerlies arrive.

 

If we continue to see trending Westwards tomorrow we could very well end up with the Scandi High keeping the Atlantic at bay allowing more undercutting and a prolonged cold spell. As I said above though, little support for this currently but todays models give some slight hope for this, whereas yesterday there wasn't any.

 

 

That is why I haven't picked one ensemble member and picked an example of a trend within the ensembles as I explained.

Do I need to post all the others or will you actually look for yourself?

I agree too early to say it is a definite trend as I have pointed out, could be a rogue set but when a signal like that pops up in the near time-frame it peeks (piques?) my interest.

Edited January 17, 2015 by Mucka

[fergieweather]

It's a more complex situation, on Wednesday for example there are times where snow looks possible at low elevations down south but others where it doesn't. Looking at the EURO4 would give you a clearer view but only from 48 hours before.

I think it's also important to note that almost without exception (stratospheric discussions aside and sometimes in discussions of severe summer convection), I only ever see forecast prognoses posted here that represent a one-dimensional story...i.e. postings showing mapped outcomes of whatever forecast parameters.

It's perhaps striking that nobody seems to post forecast profiles. Perusal of tephigram output sheds critical light on so many of the 'why doesn't Chart X show snow in location Y...?' queries. Equally, it can highlight other important areas of interest so often pondered on this thread (likely nature of boundary layer; likely tops of convective development; depth of inversions; etc etc...).

(PS Anyone unsure/wanting to learn about tephigrams and their interpretation will doubtless find lots of useful steer through a Google search... they are such a fundamentally important tool in forecasting, and in my view completely critical to examine *as well as PPN phase charts* when judging snow risk in any one location/time).

[Met4Cast]

Ensembles showing Scandi High/Some sort of Easterly - 11

 

Ensembles showing Westerly winds - 9

 

Ensembles showing a middle ground - 4

 

So currently within the ensembles there's more support for the Scandi high influence. I haven't looked into detail re: temperatures etc.. just the overall pressure pattern.

[Mucka]

I think it's also important to note that almost without exception (stratospheric discussions aside and sometimes in discussions of severe summer convection), I only ever see forecast prognoses posted here that represent a one-dimensional story...i.e. postings showing mapped outcomes of whatever forecast parameters.

It's perhaps striking that nobody seems to post forecast profiles. Perusal of tephigram output sheds critical light on so many of the 'why doesn't Chart X show snow in location Y...?' queries. Equally, it can highlight other important areas of interest so often pondered on this thread (likely nature of boundary layer; likely tops of convective development; depth of inversions; etc etc...).

(PS Anyone unsure/wanting to learn about tephigrams and their interpretation will doubtless find lots of useful steer through a Google search... they are such a fundamentally important tool in forecasting, and in my view completely critical to examine *as well as PPN phase charts* when judging snow risk in any one location/time).

 

Meto Factsheet 13 at the top of the search, is that one worth bookmarking then?

I must admit I had never heard of a tephigram. 

[Ali1977]

I have a feeling this week is going to be interesting on here, warm up towards average looking possible, howerver we are still in Jan and the NH profile is looking poised for some interesting sypnotics...

[Gael_Force]

Thanks for the replies. I guess I'm really trying to understand what the cut-off points are for where the 850/dew point/wet bulb values cease to be favourable. As pointed out by UKPaul above, the complexity means that it's almost a case of waiting until the last set of runs come out before the event to see what might emerge. I always think that the NMM modelling looks more realistic than the Euro 4, unfortunately, the only link I have for the former is centred on France and just gives a partial view of the UK.

 

Meteociel have a big range of parameters for NMM and now have close-up of regions in the UK.

 

http://www.meteociel.fr/modeles/wrfnmm.php?ech=3&mode=42&map=331

 

Example of precipitype. 

[fergieweather]

Meto Factsheet 13 at the top of the search, is that one worth bookmarking then?

I must admit I had never heard of a tephigram. 

If using NCEP products they probably output in Skew-T format (UKMO as tephis). So worth checking Skew-T tutorials (NOAA or others must have these online) for any profiles grabbed out from GFS.

[Mucka]

Ensembles showing Scandi High/Some sort of Easterly - 11

 

Ensembles showing Westerly winds - 9

 

Ensembles showing a middle ground - 4

 

So currently within the ensembles there's more support for the Scandi high influence. I haven't looked into detail re: temperatures etc.. just the overall pressure pattern.

 

Right good on you.

If you look at the progressions you will see most of those Easterly types (at least the ones that aren't gone in the blink of an eye) are because the slider is modelled to slide to the SW of UK. If you compare those with the 00z set like for like or even the 12z you will see it is a clear trend that has gathered pace this evening.

It could disappear tomorrow but one has to think it may be onto something.

I just thought it was a fairly strong signal so mentioned it for people to look out for tomorrow.

No idea which way it will go.

[nick sussex]

Can we order GEFS number 13 for tomorrow?

 

 

 The issue is how quickly that troughing over the UK separates from low heights to the nw between T96 and T120hrs.

 

You need high pressure to the ne to have a chance to ridge west earlier, even if you don't get that clean easterly theres still a chance to keep the cold longer if the troughing to the west at T120hrs on the ECM disrupts more favourably.

 

 

 

[Mucka]

If using NCEP products they probably output in Skew-T format (UKMO as tephis). So worth checking Skew-T tutorials (NOAA or others must have these online) for any profiles grabbed out from GFS.

 

Thanks very much for the pointers   

[feno13]

Ensembles showing Scandi High/Some sort of Easterly - 11

 

Ensembles showing Westerly winds - 9

 

Ensembles showing a middle ground - 4

 

So currently within the ensembles there's more support for the Scandi high influence. I haven't looked into detail re: temperatures etc.. just the overall pressure pattern.

But  there is only twenty ensembles, how have you got 24 ???

[Woollymummy]

I am interested in the possibility that this pattern we are in at the moment is round 1 in a little test of winter which has so far chilled the north of UK quite well, but has not completely changed the South into a "snowfield" (although we did catch a snow shower this morning). What is the likelihood that the European continent and Scandinavia have not yet chilled themselves enough to cool us down in the event that the winds start to allow airflow from the East, and that what may be happening is a chill, followed by a warming, then followed by a freeze at the end of the month/beginning of April? Is it possible that although the minute details of what might or might not happen on an hourly/daily basis is difficult to pinpoint, the general trend is already appearing and that whatever is happening a few ridges round the globe to our West is going to bring us a more intensely cold spell in a couple of weeks?

[Daniel*]

Meteociel have a big range of parameters for NMM and now have close-up of regions in the UK.

 

http://www.meteociel.fr/modeles/wrfnmm.php?ech=3&mode=42&map=331

 

Example of precipitype. 

Hi Ian, little off topic but NMM model is playing about, is it highly regarded? Euro4 is having none of it - is there any clarity to this? or should we just expect rain/sleet mix. Since NMM could imply disruption.

[Ali1977]

Hi Ian, little off topic but NMM model is playing about, is it highly regarded? Euro4 is having none of it - is there any clarity to this? or should we just expect rain/sleet mix. Since NMM could imply disruption.

Snowing in Swindon so could be correct

[The Enforcer]

Meteociel have a big range of parameters for NMM and now have close-up of regions in the UK.

 

http://www.meteociel.fr/modeles/wrfnmm.php?ech=3&mode=42&map=331

 

Example of precipitype.

Thanks for this - much better than the one I was using and even more detailed than the Euro4. I note that NMM seems to have identified the potential for snowfall in central southern areas and the south-east corner in the early hours of Sunday morning, whereas the Euro4 doesn't see any. Such is the volatility of the situation.

 

Also thank you to Ian F for the tephigram information.

Edited January 18, 2015 by The Enforcer

[Met4Cast]

Right good on you.

If you look at the progressions you will see most of those Easterly types (at least the ones that aren't gone in the blink of an eye) are because the slider is modelled to slide to the SW of UK. If you compare those with the 00z set like for like or even the 12z you will see it is a clear trend that has gathered pace this evening.

It could disappear tomorrow but one has to think it may be onto something.

I just thought it was a fairly strong signal so mentioned it for people to look out for tomorrow.

No idea which way it will go.

 

I think we're arguing for the same team here, haha!

 

Hi Ian, little off topic but NMM model is playing about, is it highly regarded? Euro4 is having none of it - is there any clarity to this? or should we just expect rain/sleet mix. Since NMM could imply disruption.

 

I seem to recall Ian saying the NMM was never cited in any MO briefings, though I might be wrong on that

But  there is only twenty ensembles, how have you got 24 ???

A few have Westerly winds but with the Scandi high still exerting influence over the low pressure systems by pushing them Southwards, I counted those twice

[Mucka]

Here are the full 18z ensembles with the 00z posted for comparison. clealry they have trended colder (That should say tended to lengthen the cold spell really) through the day but can we keep that going tomorrow? Also, as others have mentioned, it is notable how the op and control have repeatedly been among the mildest members even as that trend gathered pace. In that case it will be a good test of the new GFS against the old ensemble set but slightly disconcerting if the ensembles are on the money and the Op and control have missed it 4 consecutive runs thus far.

 

 

 

Also the ECM London ensembles. are they colder too? I didn't see the 00z set. Anyway they show a very gradual breakdown and still chilly out to the 25th.

 

Edited January 18, 2015 by Mucka

[Mucka]

I think we're arguing for the same team here, haha!

 

 

 

Yup.

Team Deep Freeze.   

[fergieweather]

Hi Ian, little off topic but NMM model is playing about, is it highly regarded? Euro4 is having none of it - is there any clarity to this? or should we just expect rain/sleet mix. Since NMM could imply disruption.

It's a rather dynamic situation for SE and risk of some snow on N edge still not ruled out, albeit knife-edge. High-res modelling has changed tune a few times last few days! Re NMM (and admittedly I never look at it so can't offer much opinion) is never cited by UKMO (ditto likes of Hirlam or CFS), nor have I ever heard it discussed in verbal briefings (we have these ordinarily 4x daily to hear Chief Forecaster's prognosis). So I doubt it is used in any operational sense, but will ask on views regarding it. Funnily enough, we did have NAVGEM cited a few days ago in a briefing document... first time ever that I can recall! But for the <72hr to <24hr lead, key models used for comparative purposes are Euro4, UKV (this will ultimately become primary short-lead UK model), UKMO-GM & MOGREPS; ECMWF; GFS and very often ARPEGE. From 72-144 hrs it's generally UKMO-GM/MOGREPS, ECMWF, GFS, JMA and CMC-GEM.

[throwoff]

I am happy to see the trends turning to a more long term cold, every run has been different for my little bit of the country and as much as I try to keep a national outlook I can't help but pay particular attention to my own back yard.

 

As always if we get the cold in the snow will follow, the 18z is hinting at a more prolonged spell but I am breaking my own rules of not giving the pub run too much notice if I read too much into that!

 

If the 00 and 12 tomorrow keep that trend going I think we could be in for a very interesting 10 days.

[Jason M]

More easterly influence again in the 18Z suite but the problem as always this winter is that we cant get any arctic air into the mix as all the energy is going north.

We will continue to feed off scraps unless we can get northside of the polar jet. If the jet is overriding the block we are stuck with whatever limited cold pool is available. See example below and associated 850s

http://www.meteociel.fr/modeles/gefs_cartes.php?code=13&ech=324&mode=0&carte=0

http://www.meteociel.fr/modeles/gefs_cartes.php?ech=324&code=13&mode=1&carte=0

The 850s are cold but we would only ever get a 2* easterly from that.

In terms of the 'here and now' I think this chart below illustrates why potential is limited. This is for 1pm Monday and shows the European 2m temps.

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=42&mode=9

Good luck to us trying to get anything dramatic out of that. Really this is why the initial northerly we were hoping for was so important.

In summary, I guess we just need to be careful over the coming days before we get tempted to ramp what look like otherwise good synoptics.

[Cheese Rice]

It's a rather dynamic situation for SE and risk of some snow on N edge still not ruled out, albeit knife-edge. High-res modelling has changed tune a few times last few days! Re NMM (and admittedly I never look at it so can't offer much opinion) is never cited by UKMO (ditto likes of Hirlam or CFS), nor have I ever heard it discussed in verbal briefings (we have these ordinarily 4x daily to hear Chief Forecaster's prognosis). So I doubt it is used in any operational sense, but will ask on views regarding it. Funnily enough, we did have NAVGEM cited a few days ago in a briefing document... first time ever that I can recall! But for the <72hr to <24hr lead, key models used for comparative purposes are Euro4, UKV (this will ultimately become primary short-lead UK model), UKMO-GM & MOGREPS; ECMWF; GFS and very often ARPEGE. From 72-144 hrs it's generally UKMO-GM/MOGREPS, ECMWF, GFS, JMA and CMC-GEM.

Sorry quick question 🙋

When you view the Meto precipitation maps what model is used? I've tried to cross reference with the EURO4 but the Meto invent map seems to be at a higher resolution.

EURO4

METO

Edited January 18, 2015 by Cheese Rice

[Mucka]

GFS Op starting to move toward its ensembles more and more with the idea of extending the surface cold and giving any Atlantic weather trying to move in a tough time.I wonder if there will be some decent Easterly solutions among the ensembles and the cold gets lengthened still further?

UKMO not at all interested so it will be interesting to see where the ECM goes.

Is the beast stirring from its slumber?

 

Edited January 18, 2015 by Mucka