Model Output - General Discussion

[Altohumorous]

What is very uncertain is just how far south the upper low over Scandinavia gets, the GFS suggests in the last few runs that uit can gt decently south, the ECM meanwhile only just gets the cold air in place in the south and is nowhere near as unstable as the flow the GFS runs would have been, also if we don't get it then it really reduce the risks of getting much snow at the breakdown.

There is a risk we get caught in the middle of nothing, in other words the jet runs to our south and the fronts stays outh, the upper low stays too far north and doesn't quite bring down the coldest and most unstable air, then the low pressure in the Atlantic absorbs the low and a SW surge comes up, a few hours of snow and bang back to rain and the same old story...thats a real risk IMO, something to keep a close eye on!

Yes that's kind of what I'm getting at, and you could add in the easterly to that. The high pressure over us kind of holds everything back at arm's length, as it were. And strangles the life out of the instability, at least somewhat. The advection in both the easterly and northerly does not look like really penetrating, and the risk is that this is a trend now just being modelled, so more to come. I would think our best hope is that with the fairly cold air that will be over us by the weekend, if we get any sort of instability as the high declines/moves (assuming it does!) then snow showers can form. We may well get a local event/events.

What you say about the possible breakdown also I agree, it looks like the momentum of the circulation drags in warmer air from the south. Again there's a hope that we could get a battleground if the high/relatively cold air over us and the approaching low (if and when it does) engage in the right way for us.

In the past in situations like this (Jan 1985?) despite all the blocking and cold air in almost all directions, the flow swung up a low from the southwest resulting in a sudden unexpected breakdown. Let's hope later models dont progress these possibilities

[Iceberg]

Its a real risk Kold and a growing one IMO.

I'm having a few doubts now to be honest,not about the pattern in general but the trend away from the -10 stuff

hitting us.We need that colder air to bring the snow,anything less with a warm North sea could see modification.

Places with altitude should be OK,but low lying areas near coasts MIGHT struggle.

EDIT BBC showing 4 on thur in London and 2 on Fri,make of that what you will but 4 degrees is not what i though

we'd be seeing Thur in a bitter Easterly.

But that's 2C in the very centre of London, which is probably right as a max for maybe an hr or two at peak day. Most of the outskirts of London(i.e Highgate,Richmond etc) will be 0C and more rural areas nearer -1 or -2.

[Methuselah]

Well, I've been around for quite a while...And, I don't recall too many (the usual suspects excepted ) winters in which cold spells have lasted for much longer than ten days! Indeed, how many cold winters contained a White Christmas???

We can't just write-off all the models that indicate a breakdown...It's so far in the future, it's hardly worth worrying about, IMO...

[Iceberg]

I think the more recent posts are right in pointing out what *might* go wrong, nothing bad in carming down expectations, but atm the models are still very good and look likely to remain so and haven't gone wrong.

[Altohumorous]

Its a real risk Kold and a growing one IMO.

I'm having a few doubts now to be honest,not about the pattern in general but the trend away from the -10 stuff

hitting us.We need that colder air to bring the snow,anything less with a warm North sea could see modification.

Places with altitude should be OK,but low lying areas near coasts MIGHT struggle.

EDIT BBC showing 4 on thur in London and 2 on Fri,make of that what you will but 4 degrees is not what i though

we'd be seeing Thur in a bitter Easterly.

The synoptics that I have seen in the last few days to me did not support the predicted temperatures, I was surprised by what looked like a contradiction, now it seems like the numbers are coming into line with the synoptics, (which havent really changed much)

[BLAST FROM THE PAST]

both sets of ensembles suggest 22-23rd being the breakdown dates BUT obviously don't need much od a delay to bring xmas into play.

Certainly more then a hint of a breakdown though is what I'd say, more like a screaming warning sign. I'm still thinking this is progressive as well FWIW but models do suggest a washout...thats all I was saying.

I think the breakdown being progged is plausible, but that is a long way off, but models showing deep LPs attacking the UK in deep FI is IMO and method plausible as I believe a 7-10 dfay event is likely [but it could lock in].. The GFS after the euro HP blip sends LPs on a southerly track again. ECM has LPs attacking from the SW....this IMO even if it happens is not of concern because that shouts a reload of cold after an unsettled spell.

BFTP

Edited December 14, 2009 by BLAST FROM THE PAST

[Guest North Sea Snow Convection]

With regards to the BBC forecasts, I would take their temperature predictions with a pinch of salt. I have noticed that pretty much all their readings have been at least 1-2C higher on the forecasts than actually achieved. 8C was progged for Bristol on Friday with fog lifting into cloud. Although the latter was right, it barely reached 4C. I think the main thing to look for is what the graphics show surely, how far inland the showers get and what the showers are actually of i.e. rain, sleet or snow.

Can we assume that the BBC take into account the sea temperatures in the North Sea when forecasting what type of precipitation is falling and perhaps that is why they show higher than expected temperatures. ?

In the Dec 05 easterly that occured from Boxing Day to the 29th inclusive, I distinctly remember the models, the METO and the BBC suggesting temps during the day to be between 2 and 4C. They also suggested sleet and snow showers away from coastal areas. I lived barely 2 miles from the coast then and received over 10cms of snow with minor thawing on the 27th briefly in the middle of the day and no thawing at all on the following couple of days. Point is, the upcoming set up on the temp front looks at least a match for that one - so ppn should again be snow, even for some coastal areas. The SE benefits from being closer to the continental land mass in convective easterlies or north easterlies. Northerlies benefit NE coasts more with less fetch off the wider expanse of the north sea that is up there.

I don't think the models are especially reliable in convective set-ups in terms of ppn guidance. In my own little experience, it comes down to 'now casting' and watching the dutch radar in my case to see snow streamers coming in off the north sea

Most members will know what their local conditions are like and are best using those as a guide in terms of what to expect. I largely take the models in this respect with a pinch of salt - especially when it comes to predicting snow, which is always tricky anyway for computer models and forecasters alike.

Edited December 14, 2009 by North Sea Snow Convection

[kold weather]

I think the breakdown being progged is plausible, but that is a long way off, but models showing deep LPs attacking the UK in deep FI is IMO and method plausible as I believe a 7-10 dfay event is likely [but it could lock in].. The GFS after the euro HP blip sends LPs on a southerly track again. ECM has LPs attacking from the SW....this IMO even if it happens is not of concern because that shouts a reload of cold after an unsettled spell.

BFTP

Yeah thats something I'll be keeping an eye on, the key is for the jet not to be shunted northwards, as long as it stays fairly far south then odds are eventually the upper low in the Atlantic will weaken again and that will be the shot we have to get into a colder situation again IF it does break down like that.

I'm keeping a close eye on whether we can get into the main cyclonic flow of the upper low over scandinavia around 144-168hrs, the ECM has us right at the edge of it, whilst the GFS gets us right in there. If we do get in there then we are quite likely to see several decent disturbances which would probably give several good snow oppertunities. Thats the best shot for any widespread snow.

[Iceberg]

There is alot of talk about sleet and breakdowns.

Lets look at say Thursday, this is the METO 1000-850 thicknesses from METO for Wed night/Thursday morning.

The greeny colour from the SE to the midlands and down to the Devon border is 1280-1290- This is snow thicknesses categorically under this situation.

The rest of the country is 1290-1300 which is probably sleety at lower levels but add a bit of altitude and it will be snow.

This is the METO model from only 3 days out remember not an FI chart.

The other chart is Wed Lunchtime which shows the thicknesses around the same at only 60hrs out.

Come on these are very good charts.

[Richie V]

The Icelandic IMO atlantic ocean model 00Z has the -15c 850s over eastern england on thurs afternoon and into friday.

http://en.vedur.is/weather/forecasts/atlantic/#eg=temp&type=temp

Edited December 14, 2009 by Chassisbot

[Rob K]

I think you are interpreting that chart incorrectly. The darker blue you refer to denotes 850's between -10 and -15c, with the true -15c tied up miles to the north of UK. The lowest values indicated over the UK are about -10, perhaps -11c, but that's still very cold and would see surface values at or below freezing IF they were to verify.

Yes agreed, I posted a few days ago about people being unable to read a simple colour key on these charts!

BTW there has been a lot of nonsense spouted about the 850s being "downgraded". The GFS ensemble mean has NEVER shown -15C uppers over the UK. The coldest mean for London has been -9C, and that is still what is shown around the 19th. The upper air temps have been very consistent.

[Altohumorous]

I think you are interpreting that chart incorrectly. The darker blue you refer to denotes 850's between -10 and -15c, with the true -15c tied up miles to the north of UK. The lowest values indicated over the UK are about -10, perhaps -11c, but that's still very cold and would see surface values at or below freezing IF they were to verify.

It shows a large part of England in the -10 to -15 range anyway

[Richie V]

Yes agreed, I posted a few days ago about people being unable to read a simple colour key on these charts!

BTW there has been a lot of nonsense spouted about the 850s being "downgraded". The GFS ensemble mean has NEVER shown -15C uppers over the UK. The coldest mean for London has been -9C, and that is still what is shown around the 19th. The upper air temps have been very consistent.

Just to clear up, I'm perfectly capable of reading the colour codes, prehaps my wording wasnt the best Mabe up to -15 would have been more appropiate, not that I'm picking flies or owt.

Edited December 14, 2009 by Chassisbot

[Rob K]

Just to clear up, I'm perfectly capable of reading the colour codes, prehaps my wording wasnt the best Mabe up to -15 would have been more appropiate.

Apologies. But those charts were being posted a few days ago with people misreading the scale and claiming sub -15C uppers were on the way!

[Archie_Lewis]

Hello to all.

My first post, I have been viewing net weather forums since the beginning of last winter and I have to say what a real pleasure you all have been. To the untrained eye you have all allowed me to learn and really grab a good understanding of following the UK weather paterns.

Observing you all ramp, argue, get excited, cry, feel let down and reach for the prozac has been very entertaining to say the least. You get a real understanding of the members that are the optimistic ones, the troublemakers and the members that will try and find a bad in every chart be it winter/summer.

Back to the models - Take it from me, I may be a amateur but I dont think I have ever seen charts like this so early on in the season yet im struggling to work out why im hearing talk of break downs at 144hrs.

I sat at my desk at work last Wednesday/Thursday reading your posts and im quite certain if the charts came off I should be looking at snow falling outside my window now with a very strong easterly wind.

Certain members on here are very clever and intelligent people and you know your stuff, so i find it very difficult to understand why members talk of breakdowns when we should be enjoying these wonderful charts that are Finally not in FI. After all its what we have all been waiting for in the end.

I probably will not post much, but I shall continue to view all your great posts.

Lets hope the 12z continues on a high.

Archie

[Shiny_Bottom_1]

Fo me, not liking the T+168 to T+192 on the ECM.

That low pressure seems to yo-yo around, after moving dramatically between these two time frames.

[Paul]

John Holmes' latest weekly video forecast is now online:

http://www.netweather.tv/index.cgi?action=forecast-video;sess=

[shuggee]

Hello to all.

My first post, I have been viewing net weather forums since the beginning of last winter and I have to say what a real pleasure you all have been. To the untrained eye you have all allowed me to learn and really grab a good understanding of following the UK weather paterns.

Observing you all ramp, argue, get excited, cry, feel let down and reach for the prozac has been very entertaining to say the least. You get a real understanding of the members that are the optimistic ones, the troublemakers and the members that will try and find a bad in every chart be it winter/summer.

Back to the models - Take it from me, I may be a amateur but I dont think I have ever seen charts like this so early on in the season yet im struggling to work out why im hearing talk of break downs at 144hrs.

I sat at my desk at work last Wednesday/Thursday reading your posts and im quite certain if the charts came off I should be looking at snow falling outside my window now with a very strong easterly wind.

Certain members on here are very clever and intelligent people and you know your stuff, so i find it very difficult to understand why members talk of breakdowns when we should be enjoying these wonderful charts that are Finally not in FI. After all its what we have all been waiting for in the end.

I probably will not post much, but I shall continue to view all your great posts.

Lets hope the 12z continues on a high.

Archie

Hello and welcome Archie

Just so people know in terms of any analysis posts that deserve a good airing on the forum - we'll start a fresh model thrad at 3pm in time for the GFS 12Z

[Neilsouth]

John Holmes' latest weekly video forecast is now online:

http://www.netweather.tv/index.cgi?action=forecast-video;sess=

Great forecast! , however those precipiation models are not very reliable. Some showing no snow showers in ea/se in a keen east/ne wind and cold temps

[Guest North Sea Snow Convection]

Hello to all.

My first post, .

Lets hope the 12z continues on a high.

Archie

Hello Archie

Welcome along to the forum and a very good first post

I very much agree with what you say. With that attitude regarding the models, you won't go too far wrong and your expectations will stay rationally managed. The sort of timeframe you mention at around 5 -6 days at the very max is plenty enough time to look at with any sort of confidence - and even that is subject as we know to considerable reduction when weather patterns such as these occur, when details are only going to be known in many cases just 24 hrs or so beforehand. The current modelled snowfall for some central and southern parts tomorrow is a very good example of this.

I think that there will be more surprise snowfalls springing up in the models - especially later this week and also from the weekend onwards when the northerly/north westerly takes over. Minor features could easily occur within these set-ups and we could see METO alerts for regional snowfalls just about anywhere as well as the more usually favoured spots. Lots to look out for in the many days to come

Edited December 14, 2009 by North Sea Snow Convection

[nick sussex]

Welcome Archie and may I say a great first post

I think the burning question for this evenings output is not just the more immediate term but prospects for Xmas. In a nutshell its basically down to four factors, how far the Greenland high edges west,does it weaken, how far south the jet runs and the interaction between troughing over Scandi and low pressure to the south or sw.

So these are things for us to keep an eye on in tonights output.

[TEITS]

Thanks for posting the link to Johns Forecast.

However if you don't mind me saying but I think John has made a few errors in the forecast. He states "the risk of snow tomorrow as colder air moves S" is wrong in my opinion. The risk of snow tomorrow, especially in E Midlands is because colder air from the E could turn the rain to snow on the E flank of the precip. This is nicely shown on the DP charts below.

http://www.wetterzentrale.de/pics/Rmgfs308.gif

http://www.wetterzentrale.de/pics/Rmgfs368.gif

http://www.wetterzentrale.de/pics/Rmgfs398.gif

As for Thurs/Friday again I think if the current charts verify I feel there would be more snow showers in E/SE than John suggested.

Welcome to the forum Archie.

Edited December 14, 2009 by THE EYE IN THE SKY

[Buzzit]

However if you don't mind me saying but I think John has made a few errors in the forecast. He states "the risk of snow tomorrow as colder air moves S" is wrong in my opinion. The risk of snow tomorrow, especially in E Midlands is because colder air from the E could turn the rain to snow on the E flank of the precip.

TEITS Do you think that may be because John is expecting a very slack easterly flow into the south over the next couple of days ? Perhaps not even really getting across the channel as previously expected ?

Edited December 14, 2009 by Buzzit