General Model Output Discussion

[Thundery wintry showers]

Sorry if thi is a bit off topic, but why would scandinavean high pressure the charts are showing bring any snow?

There are two ways in which a Scandinavian High can result in snow:

1. The high directs cold air towards the British Isles from the east and Atlantic weather systems push against the cold air, bringing heavy snowfalls (like some areas are seeing today).

2. The high sends an easterly flow right across to Britain and moisture is picked up over the North Sea, and if the airmass is unstable and cold enough, heavy snow showers will result, especially (but not necessarily exclusively) for eastern areas.

An easterly delivered by a Scandinavian High will, more often than not, be mainly dry and cloudy with the odd bit of snizzle here and there, because of the dry stable nature of continental air, but if the upper air is sufficiently cold then strong instability will result over the North Sea, giving sunshine and snow showers instead. The easterly at around 6-7 days' time that is being picked up by the models comes with -10C 850hPa air, making conditions favourable for the latter.

[nick sussex]

The gfs still seems more progressive in bringing the easterly than other guidance so far this evening, the ukmo does have an easterly at 144hrs but the Atlantic trough much further east. The ukmo is a more end of the line easterly with the ridge not as far west also the trough is less favourably aligned. So although some colder weather is still likely next week hard to say how long this would last for. I think we're going to have to see where the ECM goes this evening, that originally started this trend and has been consistent over the last few days.

[k19]

I agree 100% OON. The Met Office are the professionals at this game, and I would bet that their accuracy rates are a lot higher than anyone else's. Sadly, most people here and elsewhere only tend to focus on cold and snow, thus failing to take into account all the millions of forecasts that, shock horror, don't include cold and snow! Met Office forecasts aren't scrutinised in spring, summer and autumn to the extent that they are in winter and thus a lot of their work is by and large un-noticed.

Thats fair enough but the reason they are criticised in winter is because if they get it wrong the effects are noticed easily. The same goes for summer, when they most certainly are criticised about there forecasts for barbeque summers. In spring and autumn a temperature difference of 2c may not be noticed by a regular person, but in the winter especially it can make the difference between an icey day when driving is dangerous and a wet day.

[Craigers]

I'm betting on the big blue beast...

that is soooo good! i love it! haha

[weather eater]

With respect to everyone who makes a forecast on this forum (well, almost everyone) I wonder if that's actually true? I've been around here a long time, and I quickly lost count of the times something's been promised and has failed to be delivered in any way, shape, or form. Yes, we all remember the time x said it would be cold in a fortnight's time, and it was cold in a fortnight's time. But equally, there are hundreds upon hundreds of occasions when the opposite is true. I also think that an unfair emphasis is placed on their forecasting for one particular weather-type; snow. It's not the Met Office's remit to ensure their forecasting doesn't upset those of us for whom snow is the most exicting things in their lives, and I imagine they're no better or worse at forecasting snow than any other weather type.

I'm not against anyone on here, and I'm no great defender of the Met Office, but I really don't get the criticism they get, because I bet you 99/100, the mid-range forecasting is a lot more accurate than anyone's on here.

I'll second that OON, I thought this was the model thread and not one for sycophantic posts in the style of points of view or nonsense posts about how poor the MO are and how they make forecasts to cover their back,. People need to remember that the MO are a public service, when XXXX makes a bad call on NW, half the nation does not jump down their throats.

As for the easterly, there’s a lot of work needed to turn it into something special, at the moment it looks like a dull grey affair with snow flurries and not that long lived either. As usual we will have to wait and see if things can develop further.

[k19]

There are two ways in which a Scandinavian High can result in snow:

1. The high directs cold air towards the British Isles from the east and Atlantic weather systems push against the cold air, bringing heavy snowfalls (like some areas are seeing today).

2. The high sends an easterly flow right across to Britain and moisture is picked up over the North Sea, and if the airmass is unstable and cold enough, heavy snow showers will result, especially (but not necessarily exclusively) for eastern areas.

An easterly delivered by a Scandinavian High will, more often than not, be mainly dry and cloudy with the odd bit of snizzle here and there, because of the dry stable nature of continental air, but if the upper air is sufficiently cold then strong instability will result over the North Sea, giving sunshine and snow showers instead. The easterly at around 6-7 days' time that is being picked up by the models comes with -10C 850hPa air, making conditions favourable for the latter.

Could it give way to a polar low?

[johncoolj]

so it looks like a short cold snap next week lasting a few days then mildesh air again or do you think the cold air will stay longer looks like it will get colder for a few days next week then cold air is pushed back east again

Edited January 13, 2010 by johncoolj

[Thundery wintry showers]

As for the easterly, there’s a lot of work needed to turn it into something special, at the moment it looks like a dull grey affair with snow flurries and not that long lived either. As usual we will have to wait and see if things can develop further.

If we were talking 850hPa temperatures near -5C I would agree with you, but with them being around -10C I imagine the instability would lead to more in the way of convective rather than stable-weather cloud, and many areas would actually end up reasonably bright. The setup strongly reminds me of 20-22 November 1993, when after a dull grey day on the 20th, it became bright and showery on the 21st and 22nd. However with only a slack easterly flow showers would be unlikely to get very far inland, so a bit of "work" to do from that perspective.

Could it give way to a polar low?

No. Polar lows only form in northerly airstreams where the cold polar air travels over a large expanse of sea- on rare occasions you may get them in a north-easterly or north-westerly. However you can sometimes get troughs forming over the North Sea which bring more organised areas of snowfall well inland.

[nick sussex]

so it looks like a short cold snap next week lasting a few days then mildesh air again or do you think the cold air will stay longer looking here looks like it will get colder for a few days next week then cold air is pushed back east again http://www.wzkarten3.de/topkarten/fsenseur.html

It's too early to say, i think best concentrate on seeing the easterly maintained in the model output before worrying too much about the further outlook. Remember easterlies are one of the hardest things for the models to cope with and hence shouldn't be counted on until within 96hrs and sometimes even less.

Edited January 13, 2010 by nick sussex

[cooling climate]

The Met office extended forcasts change like the weather, we have been down this road before (not you and me personally).

Unless all the big models are in agreement then the Met forcasts change as often as the models.

To put it bluntly they are of no more use than their long range forcasts.

Another solid mid range run from the 12z GFS which backs up the 06z run and from what I can tell on

meteociel the UKMO t144 chart is on board as well.

Edited January 13, 2010 by grab my graupel

[ANYWEATHER]

Looks as though its still on for a very cold spell to arrive....pointless looking to far ahead because though because even the projected start of the cold spell is in the realms of FI.

[Craigers]

Looks as though its still on for a very cold spell to arrive....pointless looking to far ahead because though because even the projected start of the cold spell is in the realms of FI.

not just that but models always seem to push the easterly back east when it goes into default mode in FI

[ANYWEATHER]

The Met office extended forcasts change like the weather, we have been down this road before (not you and me personally).

Unless all the big models are in agreement then the Met forcasts change as often as the models.

To put it bluntly they are of no more use than their long range forcasts.

Another solid mid range run from the 12z GFS which backs up the 06z run and from what I can tell on

meteociel the UKMO t144 chart is on board as well.

------------------------------------------------------------------------------------

I totaly agree, you only have to look at there summer and winter forecasts which verify as usually inaccurate [ie last summer and this winter] I think the Netweathers long range forecasts have been a lot more accurate!

Edited January 13, 2010 by ANYWEATHER

[Maz]

There are two ways in which a Scandinavian High can result in snow:

1. The high directs cold air towards the British Isles from the east and Atlantic weather systems push against the cold air, bringing heavy snowfalls (like some areas are seeing today).

2. The high sends an easterly flow right across to Britain and moisture is picked up over the North Sea, and if the airmass is unstable and cold enough, heavy snow showers will result, especially (but not necessarily exclusively) for eastern areas.

An easterly delivered by a Scandinavian High will, more often than not, be mainly dry and cloudy with the odd bit of snizzle here and there, because of the dry stable nature of continental air, but if the upper air is sufficiently cold then strong instability will result over the North Sea, giving sunshine and snow showers instead. The easterly at around 6-7 days' time that is being picked up by the models comes with -10C 850hPa air, making conditions favourable for the latter.

Arguably there is a "third way":

The Scandi high is usually held up by a low pressure over southern Europe. This can move towards us in the Easterly flow giving frontal snow spreading SE to NW over the country. Much as was forecast for last weekend at one stage. The instabilty associated with this often acts to beef up the showers off the North Sea.

[Thundery wintry showers]

Regarding the Met Office's outlooks, I'm not sure that their forecasts are significantly more accurate than everyone else's- some of the other forecasts out there may or may not be similarly accurate. However I doubt anyone could realistically claim to be more accurate than them.

Their 6-15 day forecasts have actually been pretty good considering how far in advance they are (all models taper off in accuracy after 5 days out, so having access to all of the supercomputers under the sun doesn't help if all of the models are erring in a similar way!). They chop and change sometimes, but most of the time the general trend has tended to be correct.

The scenario of a brief easterly followed by a breakdown from the SW is completely plausible and is supported by today's GFS 12Z operational. However, there is the possibility that the attempt at a breakdown from the SW could fail, leaving us with a more prolonged easterly spell, as the strength of continental blocking is extremely hard to forecast well in advance.

[Stu_London]

With respect to everyone who makes a forecast on this forum (well, almost everyone) I wonder if that's actually true? I've been around here a long time, and I quickly lost count of the times something's been promised and has failed to be delivered in any way, shape, or form. Yes, we all remember the time x said it would be cold in a fortnight's time, and it was cold in a fortnight's time. But equally, there are hundreds upon hundreds of occasions when the opposite is true. I also think that an unfair emphasis is placed on their forecasting for one particular weather-type; snow. It's not the Met Office's remit to ensure their forecasting doesn't upset those of us for whom snow is the most exicting things in their lives, and I imagine they're no better or worse at forecasting snow than any other weather type.

I'm not against anyone on here, and I'm no great defender of the Met Office, but I really don't get the criticism they get, because I bet you 99/100, the mid-range forecasting is a lot more accurate than anyone's on here.

I couldn't agree more.

Even the forecasters on here that are not biased towards cold weather would struggle to beat the met office and it's hardly suprising given the resources available.

I think many would be suprised just how poor the verification of some of the predictions of the hero-worshipped members if data was collated in the same way as the models are judged.

Goes back to the old adage of people prefering what they want to hear rather than fact.

Back on topic - the 12z shows the easterly coming in nicely during the higher res part of the run and then retreating pretty quickly in FI. I'd say an easterly of sorts was slightly odds on now, however a long lived event with severe weather attached to it is much less likely - maybe 1 in 6 chance at this stage

[Frosty.]

I think the GFS 12z op run is as good as we could dare hope for considering the current cold spell is now on it's last legs and we will all be turning less cold for friday and the weekend with temps going above 5c 41f and even a few degrees higher than that in places. Saturday looks dominated by a slow moving band of heavy rain and strong southerly winds but sunday the winds look lighter and still a chance of snow on northern hills and the scottish mountains. Next week looks promising on the gfs 12z for another cold spell but not as severe as we have had recently and for much of FI the cold air hangs around in the north and east with no sign of the cold block being blasted away.

[PB22]

The Met office extended forcasts change like the weather, we have been down this road before (not you and me personally).

Unless all the big models are in agreement then the Met forcasts change as often as the models.

To put it bluntly they are of no more use than their long range forcasts.

Another solid mid range run from the 12z GFS which backs up the 06z run and from what I can tell on

meteociel the UKMO t144 chart is on board as well.

The extended forecasts do change regularly, but to be honest it would be more of a surprise if they didn't because we all know that medium to long range forecasting is very difficult and subject to big changes. (FWIW I still maintain the 6-15 day forecasts are a day behind the latest developments and today's release merely reinforces my opinion) In terms of short to mid range forecasts though, the Met Office rule.

Here's the 12Z GFS mean charts from the ensembles for T+138:

http://91.121.94.83/modeles/gens/run/gens-21-1-138.png?12

http://91.121.94.83/modeles/gens/run/gens-21-0-138.png?12

[Avain]

On this image of Sundays UKMO chart

What is the significance of the black line that separates the blue isobars from the orange?

[BLAST FROM THE PAST]

I really am far from convinced at the moment, that a further cold spell, in terms of length to what we have just had, is more than an operational run.

Correct and don't be. The renewed cold shot is IMO a continuance of the current cold spell and will last to 24th. Then the real mild breakdown will arrive, I wish to state that this next cold will NOT see the month out, the Atlantic will have its moment 25-31. Re the Stratosphere warming, this may well occur and we see a renewed cold attack 'very early Feb' [trigger LP end of Jan. For those that remain very cautious re next week, wise but something I am very much homed in on and have been for sometime, I think the models are correct today thus far re general trend for next week.

BFTP

Edited January 13, 2010 by BLAST FROM THE PAST

[Thundery wintry showers]

Arguably there is a "third way":

The Scandi high is usually held up by a low pressure over southern Europe. This can move towards us in the Easterly flow giving frontal snow spreading SE to NW over the country. Much as was forecast for last weekend at one stage. The instabilty associated with this often acts to beef up the showers off the North Sea.

True, I forgot about that one! I think that one can deliver as long as the whole lot doesn't move north too quickly, in which case you can get frontal snowfalls from the main band and frequent heavy snow showers to the north of it. The main issue I have with it is that the frontal band often turns to sleet or freezing rain on its southern flank, leading to icy conditions, and especially if it all gets shunted north quickly allowing more modified air in from the SE. I vividly remember a similar thing happened across north-east England on 26/27 January 1996 resulting in sun & snow showers on the 26th and prolonged snow on the 27th, but by the 28th, the snow had all melted near the east coast.

It doesn't look likely to be one of the options for next week though.

[VillagePlank]

On this image of Sundays UKMO chart

What is the significance of the black line that separates the blue isobars from the orange?

The boundary between low and high pressure. Neither high, nor low.

[swilliam]

I'm betting on the big blue beast...

Very amusing - the JMA has the Lochness monster about to eat Iceland (serves them right for losing all our councils money).

The actual output on the JMA look pretty good though with no early breakdonw on the Easterly next week.

[The PIT]

That high is rather a tough boy isn't it. Doesn't want to get shifted away and pushes back in FI to deep FI. Again a sudden reversal from yesterday. I wonder what the later ECM thinks of it all.

[PB22]

The GFS Control run gives us the shortest easterly ever and once again on the ensembles there is good support for a quick return to southwesterlies in FI. This trend is almost as consistent as the trend for a renewed colder slot next week. All subject to change though.