General Model Output Discussion

[conor123]

Is there not any chance Tuesdays low could power up more and slam into the Midlands for once?

[azores92]

well could there be a reload at the end of the week!!!

that shows milder air working in to the country with the all too familiar icelandic low and high pressure proving stubborn to the east.

[PubliusEnigma]

I think this looks rather interesting.

signs of some Sub 528 Dam air coming back to the SE corner, with snow ?

I think beyond thurs friday the MO havent a clue what will happen. ?!

[maelstrom99]

Hello,

Looking at the GFS 06z would this be a resumption of normal service or does the orientation of the lows mean something more wintery because the winds are more SE?

Thanks

[weather eater]

May I suggest that precipitation forecasts are always wrong to some degree, but it's simply that when it's rain predicted, it's very rare for people to care and to take any notice whatsoever? I've rarely heard of anyone berate the Met Office for predicting 5mm of rain overnight, when it fails to turn up, yet when it comes to snow, there are many on here (and I'm not suggesting you're one of them) for whom it's the end of the world.

Very true OON, I suspect that's happening all the time, not just by the MO but also by forecasters on NW, amateur or professional. It works the other way, anybody on NW who predicts cold and gets it right, is lauded as some sort of weather Guru, forgetting the umpteen times they got it wrong on previous occasions. The MO do a fantastic job in my books and I don't see why they should be slated when some whose record is not a fraction as good get countless posts full of praise.

[Nath]

Looking at the different models it looks like an incredibly difficult situation to call next week, and the smallest changes today will render even T72 completely different.

Its times like this that make me feel in awe of nature, even supercomputers cant second guess her.

[Osbourne One-Nil]

It works the other way, anybody on NW who predicts cold and gets it right, is lauded as some sort of weather Guru, forgetting the umpteen times they got it wrong on previous occasions. The MO do a fantastic job in my books and I don't see why they should be slated when some whose record is not a fraction as good get countless posts full of praise.

Yep! I've almost chewed my tongue off, it's been bitten that often recently.

Now I'm no model expert (in case anyone wondered) but to my eyes, what we have coming up could, over some winters, have provided lots and lots of excitement, so a sense of perspective is going to be needed.

[Methuselah]

Very true OON, I suspect that's happening all the time, not just by the MO but also by forecasters on NW, amateur or professional. It works the other way, anybody on NW who predicts cold and gets it right, is lauded as some sort of weather Guru, forgetting the umpteen times they got it wrong on previous occasions. The MO do a fantastic job in my books and I don't see why they should be slated when some whose record is not a fraction as good get countless posts full of praise.

I agree. I think a great many of us :lol: (and the models) have been flummoxed by the degree mixing/turbulence caused by the strength of the wind? Just now, it's sunny @ -9C up here; but, once the wind arrives, temps will shoot up - I've no doubt...

[derrylynne]

My take looking at the latest models is that although it has turned milder - it is in no way going to be warm. There is also the prospect of more snow on occasions. These themselves maybe broken by slightly warmer interludes where the snow turns back to rain in places - only to turn back to snow the next day. In no way do I see these models as warm. I have also noticed that fridgid air is never ever too far away from us over Europe, and it will not take too much of a push to shove it back over the UK. The jet is also forecast to stay on it's holidays to the south of us - so the prospect of full atlantic mild westerlies just does not look an option to me. Now I am not an expert and there are folks on here much more experienced. So some of your guys comments on mine will be welcome....

[jethro]

BFTP - just seen your post about the cold whimpering out from the SW over the coming days, does this mean your expectation of a battle ground scenario around the 14th has now diminished somewhat?

[Thundery wintry showers]

Yes, ironically today looks like being the warmest day for a while over most of the country. In central and southern parts of England, in particular (barring the extreme south) it is likely to stay close to freezing by both day and night next week. For snow we will be relying upon mainly light precipitation coming in off the North Sea, I think, as those Atlantic systems look like they aren't going to get far beyond the far SW.

[J10]

It's constantly reinforced in this forum that anything beyond the next 3 days or so is to be regarded as FI, so any predictions made a week ago would fall into that category. It's also been said that snow amounts and locations can change within hours of "now", so I think many people have been basing their expectations on forecasts made during past 24 hours. Yesterday, the BBC forecasts were suggesting widespread light snow throughout the day right across the southern half of England and Wales, with significant amounts in a number of places. Today, they've downgraded that to being little more than snow flurries here and there with the possibility of something more significant overnight on some hills. I believe that's the reason for the consternation.

As others have commented, I feel there's a gap in these forums, when there's uncertainty in what might happen, where what models are saying regarding the weather in the near/immediate future is either ignored or lost in a sea of FI posts. It would also be interesting to see more posts within a day or two of the event comparing what actually happened to what the models predicted would happen, thus reviewing which models called it best. There's an understandable concentration on what's to come rather than what's been but, as far as models are concerned, analysing their performance is arguably more important than their future predictions. Perhaps the forum structure might be reviewed to compartmentalise things more, although I appreciate more forums would mean more work for the mods.

Just my two penneth! :lol:

Slightly off topic I know but it sort of answers your point about comparing the forecast to the actual event, which I think is a good idea. Over much of South Wales this morning, there has been consistent but light snow, exactly as forecast by the models.

It could of course be argued that the warnings never actually matched up to the models. However I agree that there has been too much criticism of the Met Office, the UKMO model and FAX charts have forecasted this spell as well as any other model. Would be really like to be stuck with the GFS?

[Duane S.]

Upgrades, downgrades and, so it would seem, a bit of another general downgrade this morning.

The models are strugling at the moment, there can be little doubt about that. Against my initial thoughts that we would be looking at a 'battle to end all battles' this week, I now fear this cold spell end very forgetably. BUT... possibly only temporarily??

With the Atlantic not having a grat deal of 'umph' to it at present, it would be a bit of a shame if it was allowed to simply waltz on in by our block. We are certainly not talking about any immenint return to raging SouthWesterlies here but a short-medium term general warm up to near (but still lower than) average temps, for the South at least, would seem to be on the cards. There does seem to be a bit of a 'no mans land' scenario come about T+144 with both sides pausing for breath and us sat in the middle, this is the crucial point, what happens next??? I suspect the models will throw up all sorts of permatations for that over the coming few days.

The AO and NAO look set to remain negative but perhaps a gradual climb towards a more average state (although still negative) looks set for both come the next 7 days. I think that in 7-10 days time we are however going to see the NAO become more negative than the AO. But that remains to be seen...

As for the impending Atlantic attacks this coming week...

Attack number #1 on Tuesday: The problem is that whilst it is similar to what happened in Feb 1978, i.e. with an occluded front moving up from Biscay with an associated trough, the temps will have been chipped away at too much prior to the event and the front shows no signs of stalling for most places to benefit, IMO. The block seems edge back East with consumate ease before the LP is eventually rebuffed back into the parent system to regroup. 'Attack' number #2 on Thursday? This is where it COULD get interesting and may end up undercutting. I also think that by this time we will start to see the first tentative signs of the High Pressure building back in from the East (partially supported by teleconnections). If the Atlantic can be held at bay I can see a very interesting final third to January.

So I think we are looking at a disappointing start to the week (although there will be snow, potentially big falls for those on high ground) with regards snow and temps but the end of the week heading into the weekend could see the START of a reload and an Easterly to follow.

[West is Best]

Yes i saw the BBC forecast last night for wiltshire area today

light snow 2 -5 cm , strong winds drifting snow and -3 to -4 quite widely

WRONG WRONG WRONG

Well 100 miles west and it would have been spot on, except that we have had much more snow than that this morning. 10-15cms and still snowing now.

What OON said is so true: we only notice because it's snow not rain.

Does look like a breakdown coming but boundary snow could be extensive and intensive.

Edited January 10, 2010 by West is Best

[johnny1972]

Folks

The ensembles for my location have been progging the breakdown and rise in temps to start from 13th Jan 10 for over a week now. However 2day the temp sits at 4C, with a dew point of 0.5C and wet bulb of 2.5C (not condusive for snow). Given according to the models the 850 uppers are currently -10 or below i find this difficult to understand. I certainly would have expected temps at freezing or below. This is the second time with uppers at that value that this has happened in a week here. I have had colder weather with warmer uppers. The forecasts have got this badly wrong for some from what i have read today. Even on the webcams for aviemore and loch morlich the temp is above freezing and a slight thaw has begun.

Can someone please explain in their opinion has warmer air somehow got into the mix earlier than expected or what is the cause of todays higher than predicted temps??

Edited January 10, 2010 by johnny1972

[Frosty.]

Nice to see someone actually discuss the models for once frosty, spot on post there, remember countryside areas will be colder than urban areas so hardly any thaw likely for countryside areas.

Excellent trends on the models this morning esp ECM for our blocking high to our east to remain in place and stop a mild invasion, its amazing to watch all the mild atlantic air filtered out on GFS 06Z so we have a mass of cool to cold air to our west, watch out for later in the week for the High to our east to edge further west on each subsequent GFS run.

http://www.wetterzentrale.de/pics/Rtavn2162.png

Thanks Eugene,

I just took a look at the latest fax chart for next thursday and it still shows the uk in cold air with the 528dam line close to the southeast and some snow in places with overnight frosts. We have lost the extreme cold but it still looks cold all next week with just the sw at risk of milder incursions, I think the further outlook suggests a less cold trend making more inroads into the uk from the southwest so that northeastern britain hang on to the cold for longest but for the next 7-10 days I can't see much more than a slow daily thaw and the nights will probably be sub-zero in most inland areas.

[J10]

Yes, ironically today looks like being the warmest day for a while over most of the country. In central and southern parts of England, in particular (barring the extreme south) it is likely to stay close to freezing by both day and night next week. For snow we will be relying upon mainly light precipitation coming in off the North Sea, I think, as those Atlantic systems look like they aren't going to get far beyond the far SW.

I was looking at the ECMWF ensembles on Meteociel, I know they are the De Bilt ones, but look at the temperatures being forecasted by both the Operational and the control run. Clearly some uncertainty with many of the ensembles going somewhat milder, but clearly no certainty in the end to the cold weather.

http://www.knmi.nl/exp/pluim/vijftiendaagse/index.html

[Mark Bayley]

Interesting developments in the stratosphere, currently below average however the 10hpa is forecast to warm with the 30hpa following on behind. It should help maintain a -AO and keep the polar vortex disrupted, or preventing it from gaining to much strength. Should it materialize then it might be something to watch as we head towards the end of Jan and into Feb?

In the short term and i can't see much in the way of mild, less cold but not above average. ECM is interesting and remains on the cold side throughout! Am i right in thinking that towards the end of the run we see a return of some sunshine and perhaps some wintry showers?

Edited January 10, 2010 by mark bayley

[Thundery wintry showers]

yes the term-lost the deep cold seems about right to me.

Its pretty obvious I would have thought that if temperatures are above freezing then some kind of 'thaw' Will lake place. Unless the temperatures get above about 4C then its a slow one certainly not rapid.

The weather seems to show no signs of becoming mild by definition in any time scale.

Regarding the precipitation-I continue to suggest that slight intensity-outside the exceptional cold values at 850mb for most of last week, almost always lead to a 'wintry' mix-rain, sleet, frozen raindrops, rain. For snow to fall in the conditions we are now in then height is required and/or intensity. Both will give snow, maybe wet rather than the dry variety of the past week but snow but not with very slight intensity at any low level, near the sea or not.

I agree with a lot of what you've been saying in recent posts, but I think it is possible to get light snow even with higher 850s in some circumstances. In the Tyne & Wear area I've known light snow flurries with 850hPa temperatures of around -4 or -5C- this happened in the early December 2008 cold snap.

But I certainly agree that if the word "marginal" slips in, then intensity is paramount if we are to see anything significant on the ground.

[WelshSnowFan]

I was looking at the ECMWF ensembles on Meteociel, I know they are the De Bilt ones, but look at the temperatures being forecasted by both the Operational and the control run. Clearly some uncertainty with many of the ensembles going somewhat milder, but clearly no certainty in the end to the cold weather.

http://www.knmi.nl/e...agse/index.html

I can remember GP saying yesterday I think in the Model Technical Discussion thread, to expect model uncertainty during the next couple of days. Is this tying in with GP's thoughts as he has been on the money with his thoughts for several weeks now. Just a thought, not straw clutching

Just found it - GP's comments on the 8th Jan -"High chance that model performance will dip over the next few days."

WelshSnowFan (Swansea)

Edited January 10, 2010 by WelshSnowFan

[johnholmes]

I've done a quick blog to summarise some of the parameters regarding why the rain not snow for so many parts of England.

Its far from clear other than it being predicted always to be starting to become 'marginal' from today.

I prefer to investigate what the reasons why its gone wrong-more so for some than others but I have to say the answers are far from clear, and that includes using actual not predicted data. Anyway take a look.

I agree with a lot of what you've been saying in recent posts, but I think it is possible to get light snow even with higher 850s in some circumstances. In the Tyne & Wear area I've known light snow flurries with 850hPa temperatures of around -4 or -5C- this happened in the early December 2008 cold snap.

But I certainly agree that if the word "marginal" slips in, then intensity is paramount if we are to see anything significant on the ground.

the difference Ian, I suspect, is you are talking largely unstable air-this is not largely unstable air-its got an upper warm front over the top of it and the very low values at 850mb were disappearing yesterday.

Predicting snow with this type is incredibly difficult. Earlier this week was a piece of cake in comparison.

[johnny1972]

I've done a quick blog to summarise some of the parameters regarding why the rain not snow for so many parts of England.

Its far from clear other than it being predicted always to be starting to become 'marginal' from today.

I prefer to investigate what the reasons why its gone wrong-more so for some than others but I have to say the answers are far from clear, and that includes using actual not predicted data. Anyway take a look.

the difference Ian, I suspect, is you are talking largely unstable air-this is not largely unstable air-its got an upper warm front over the top of it and the very low values at 850mb were disappearing yesterday.

Predicting snow with this type is incredibly difficult. Earlier this week was a piece of cake in comparison.

John

I think that vaguely answers my post from further back on this page. It seems very strange today. Thanks.

[johnholmes]

oddly enough-what has to be guarded against now-is to go too far in the less cold direction.

All forecasters need to take stock-look at what is ACTUALLY happening both on the surface and in the upper air-and from some distance from the UK shores, all round-what is happening-have the models got a good hold on that. The 12z input should address any problems from early on so hopefully the 12z output from GFS/Extra and UK Met/NAE should pick up on anything. Also any forecaster will also be looking back at basic forecasting.

So interesting to see what the output shows for the next 24-48 hours later this afternoon.

[J10]

oddly enough-what has to be guarded against now-is to go too far in the less cold direction.

All forecasters need to take stock-look at what is ACTUALLY happening both on the surface and in the upper air-and from some distance from the UK shores, all round-what is happening-have the models got a good hold on that. The 12z input should address any problems from early on so hopefully the 12z output from GFS/Extra and UK Met/NAE should pick up on anything. Also any forecaster will also be looking back at basic forecasting.

So interesting to see what the output shows for the next 24-48 hours later this afternoon.

Again slightly off topic but relevant in my view, the latest TV forecast for Tuesday was very vague, and they are deliberately taking a step back in order, and effectively start nowcasting as you say. Watching the event come into the time frame of the NAE should also be very interesting.

[Thundery wintry showers]

Interesting developments in the stratosphere, currently below average however the 10hpa is forecast to warm with the 30hpa following on behind. It should help maintain a -AO and keep the polar vortex disrupted, or preventing it from gaining to much strength. Should it materialize then it might be something to watch as we head towards the end of Jan and into Feb?

In the short term and i can't see much in the way of mild, less cold but not above average. ECM is interesting and remains on the cold side throughout! Am i right in thinking that towards the end of the run we see a return of some sunshine and perhaps some wintry showers?

To get a return of the sunshine-and-snow-showers sort of regime we had during the first 9 days of January we would need to see those Atlantic systems get held out west, and a renewed pool of cold upper air come across from the east- sub -8C 850hPa and sub 522 dam thicknesses (the latter are missing from today's episode). That would produce enough instability over the North Sea to give clear intervals and showers rather than stratocumulus trapped under an inversion.

I can't be sure of the thicknesses and 850hPa temps associated with the ECMWF T+216 and T+240 charts, but they are certainly along the right lines for producing that scenario. However at this range it is just a slight possibility, and the Atlantic may be too strong to allow a reload to head straight across like that.