Model Output Discussion 12z 30/11/2012

[Tim Bland]

If its snow your free then IMO the 00z ECM is best case scenario. Personaly I would hate the high to build over us as it means nill chance of snow an the invariably it will topple to our SE and let the Atlantic in meaning we have to wait for another 2 weeks or anything interesting. I hope we continue to see trough disruption and low pressure over the uk. Fingers crossed ECM sticks to its guns in an hour

[Weather Boy]

I think weather eater is right - 3 gfs runs, 3 different ideas for post 120hrs... My knowledge of the strat and vortex etc is low but I cannot see a high +nao from the strat...

FI gfs to be an outlier?

Given what we (or rather I) have recently learnt about GFS post T+192 (and probably less in these situations), namely that METO ignore it at that range, is there any point in thinking about it too much?

I know that this is a model discussion thread, but if the GFS is totally ignored by the experts at long range, is there any reason we should dwell on it? GP reckons that at that range the Op should be ignored and the ensembles looked at, but then other more experienced posters say that the ensembles are "misleading" which leads me slightly confused and wondering whether we should just look at teleconnections and other signals (e.g the strat) that GP has used in his long-range forecast.

...but then others say that the GFS is picking up trends. Is it in this situation though? These models are computers designed to look for a solution. It seems to be programmed to go for a vortex reformation. The "problem" is a shattered vortex: the "solution" is how does it re-form. It looks from the GFS in low res, that it doesn't really occur to the computer that it might not re-form.

Edited November 30, 2012 by Weather Boy

[cyclonic happiness]

If we do get a big high over us it'll do a few good things in my opinion.

First it'll allow the flooded areas to dry out somewhat, second, it'll freeze and cool the ground so any snow that come later will have a much better chance of sticking.

And it'll also give us some nice hard frozen ground so we don't trudge around in mud like I've been doing for the last few weeks.

Not a smidgion of consistency in any of the models at the minute, they're all wrong, we've not the vaguest clue where we'll be in 2 weeks time?

[Frosty.]

GFS is the worst 12z run we have seen in a long time from a cold point of view post 144hrs. Trend seems to be to build in a mid latitude blocking high pressure.

What's so bad about that? we can then develop our own homegrown pool of cold air with light winds, frost and fog..and we can dry out after all the floods

But don't trust a gfs op run beyond T+144 hours since there is so much that can change in the closer range which will then have a bigger impact later.

A true weather fan accepts any weather type, good and bad.

Edited November 30, 2012 by Frosty039

[Tom Jarvis]

can i pose a question what if the tropical lows dont actually form and it being a phamtom low that the moddels have just chucked in

steve murr could you shed some light on this pls

Edited November 30, 2012 by Tom Jarvis

[stainesbloke]

Hello, new member here tho I've followed discussions on the forum for quite a long time. Just wanted to say the charts and trends have been great recently with some really interesting posts, I've been learning a lot! Looks like the next few weeks are going to be fun to watch, some potential for an early winter cold spell with snow, some nice winter sun and frosts/fog....loads better than the grey, drizzly days we often get at this time of year.

[IDO]

I was looking at the Control run, as that has been much better when the GFS op has been pants for snow. It keeps the tropical low to our SE, before it gets mixed out when trop low number two makes an entrance.

http://modeles.meteo...-0-1-180.png?12

The end pattern is very similar to the op with heights building over the UK, though in FI the high migrates favourably for an easterly of sorts:

The mean tells a similar story, though as expected not as progressive: http://modeles.meteo...21-1-192.png?12

Mean at T276: http://modeles.meteo...21-1-276.png?12

At T312: http://modeles.meteo...21-1-312.png?12

Mean Surface temps: Day 8-15 :

http://wxmaps.org/pix/temp4.png

Not far from average.

A tentative pattern from the GFS.

Edited November 30, 2012 by i'm dreaming of...

[Frosty.]

Hello, new member here tho I've followed discussions on the forum for quite a long time. Just wanted to say the charts and trends have been great recently with some really interesting posts, I've been learning a lot! Looks like the next few weeks are going to be fun to watch, some potential for an early winter cold spell with snow, some nice winter sun and frosts/fog....loads better than the grey, drizzly days we often get at this time of year.

Hi stainesbloke,

Hope you enjoy posting here, the models are looking promising for more cold weather to return through next week and then it looks like becoming more anticyclonic, probably for a week or two, hopefully we can tap into a cold air source from the east and north during that period but hard to nail where the high will end up for the time being.

Edited November 30, 2012 by Frosty039

[Jaffusmaximus]

Could one of the pros tell me at what time + on a chart is (especially GFS) not worth reading much into. And rank the charts in order of most likely to be close to being accurate .

[zubzero]

can i pose a question what if the tropical lows dont actually form and it being a phamtom low that the moddels have just chucked in

Id like some more info on that low to? Cant remember ever seeing a low form and push west like that at this time of year. Are there any past charts that show something similar?

[weatherguy]

Looking at the ensembles, it would appear that FI seems to start at around the 5th/6th December

Remaining very cold in the short term (lots of frost about today!), and promising synoptics for cold potential through December.

[Frosty.]

Could one of the pros tell me at what time + on a chart is (especially GFS) not worth reading much into. And rank the charts in order of most likely to be close to being accurate .

Here you go, this seems to work

[chris55]

GFS very close to a huge snow event for those in the south,

http://www.wetterzentrale.de/pics/Rtavn1442.png

http://www.wetterzentrale.de/pics/Rtavn1441.png

What happens to this Little cut off Low could be very interesting, We need it to hold and push energy southwards (like GFS) rather than just filling/disrupting (like UKMO) One to watch and the slightly unusual nature of the set up may give the models some headaches.

[Methuselah]

These atlantic lows showing on the GFS are FI material. The initial one has already lowered in intensity as opposed to yesterdays GFS and also todays 6z output, I do not see them happening in the form that the GFS is showing at all : FI still at +48 for me, especially as these lows have so much impact on the pattern to follow.

From experience, I strongly suspect that you're right, as even the trajectory of the 'Channel Low' is far from settled; it could easily end-up five-hundred miles' further north or south. It may even fail to influence our weather altogether?

IMO, with everything seemingly on such a precipitous 'knife-edge' anything past T+120 is literally fantasy!

[bluearmy]

should really wait for the ecm but having looked throught too much output today i'll take a punt on where the modelling is going.

next week looks set with the trough over or just east of the uk. slowly edging se as pressure builds across the top, mainly from the atlantic though possible with help from the ridge to the east. thereafter, a further depression crosses the meridian to the north of the uk and then dives se as our high retrogresses somewhat. therefore a gap between the heights to our east and the ridge across the uk which the trough drops into. it then circulates in a clockwise direction around the retrogressing block to end up somewhere between se uk and austria. this takes us to approx 12th december with low heights to our se and high heights to our nw and north.

there are a few gefs members which follow this solution.

[stainesbloke]

GFS very close to a huge snow event for those in the south,

http://www.wetterzen...s/Rtavn1442.png

http://www.wetterzen...s/Rtavn1441.png

What happens to this Little cut off Low could be very interesting, We need it to hold and push energy southwards (like GFS) rather than just filling/disrupting (like UKMO) One to watch and the slightly unusual nature of the set up may give the models some headaches.

If the air being dragged in from the East is cold enough and the centre of the low goes through the Channel then the South would get a very good chance of seeing heavy snow. These types of low are really hard to forecast even at t48 so it could disappear in upcoming runs...how good if it came off tho!

[Cheshire Freeze]

should really wait for the ecm but having looked throught too much output today i'll take a punt on where the modelling is going.

next week looks set with the trough over or just east of the uk. slowly edging se as pressure builds across the top, mainly from the atlantic though possible with help from the ridge to the east. thereafter, a further depression crosses the meridian to the north of the uk and then dives se as our high retrogresses somewhat. therefore a gap between the heights to our east and the ridge across the uk which the trough drops into. it then circulates in a clockwise direction around the retrogressing block to end up somewhere between se uk and austria. this takes us to approx 12th december with low heights to our se and high heights to our nw and north.

there are a few gefs members which follow this solution.

I've run through the GEFS ensembles and it's a real struggle to find an ensemble member worse for cold prospects post 168hrs than the op run. Infact there is a remarkably strong signal for Iceland/Greenland height rises 10 days + in those ensembles. The one caveat being it's a looooong way out. It's around about a 60/40 split in favour of cold prospects week 2 +. It's an all or nothing situation in light of what I can see......either a raging +NAO & vortex energy around Greenland or the complete opposite.

Edited November 30, 2012 by CreweCold

[chris55]

Looking at the GEFS to see how the individual runs deal with this Low there are many options. (more than I have highlighted here)

Snow event!

Misses to the south,

Ridge building ahead,

[snowmadchrisuk]

From experience, I strongly suspect that you're right, as even the trajectory of the 'Channel Low' is far from settled; it could easily end-up five-hundred miles' further north or south. It may even fail to influence our weather altogether?

IMO, with everything seemingly on such a precipitous 'knife-edge' anything past T+120 is literally fantasy!

If that channel low does come further North though it will also drag some very mild air with it ... You have to have it in exactly the right place for an all snow event,

[Methuselah]

If the air being dragged in from the East is cold enough and the centre of the low goes through the Channel then the South would get a very good chance of seeing heavy snow. These types of low are really hard to forecast even at t48 so it could disappear in upcoming runs...how good if it came off tho!

Welcome n-w stainesbloke!

[Geordiesnow]

I think its going to be hard to speculate the details of next week in all honesty, there appears to be alot of factors coming into play but all the models still point to a cool perhaps turning colder by mid-week set up. Its one to keep an eye on though.

As we know from the past week, the output is subject to change although the trends don't really so the chances of high pressure ridging in is fairly high but its not a certainty.

[fergieweather]

If that channel low does come further North though it will also drag some very mild air with it ... You have to have it in exactly the right place for an all snow event,

Quite. Exeter's latest comment on it: "....a moderate prob of a more organised spell of rain/sleet/hill snow running E’wards across southern and western areas...."

[Tom Jarvis]

If that channel low does come further North though it will also drag some very mild air with it ... You have to have it in exactly the right place for an all snow event,

Looking at the GEFS to see how the individual runs deal with this Low there are many options. (more than I have highlighted here)

Snow event!

Misses to the south,

Ridge building ahead,

If the air being dragged in from the East is cold enough and the centre of the low goes through the Channel then the South would get a very good chance of seeing heavy snow. These types of low are really hard to forecast even at t48 so it could disappear in upcoming runs...how good if it came off tho!

can i just say we dont even know if these lows are even going to form out in the atlantic. i follow one of the people storm chaser that live in america on facebook he says the waters are too cold and that it is highly unlikely but it is possible. so mabe we should just wait and see if the low forms in the coming days. you never know tomorrow it may not even appear on the moddeles at all

Edited November 30, 2012 by Tom Jarvis

[chionomaniac]

I think that one thing that is likely over the coming 10 days is a period of time is that energy is likely to be transferred across the pole from Siberia to Canada. When this occurs heights are likely to be lowered temporarily around the northern half of Greenland. This may appear in the models as if zonality is likely to set in - but this is not likely as it will only be a temporary feature. Any mid Atlantic height rises I suspect will be pushed eastwards. Whether this can lead to something more substantial over Scandinavia depends very much on the amount of displacement the vortex undergoes. I can't see any height rises powering into Greenland until the vortex is cleared westwards fully into the Canadian segment ( if that occurs).

[Chess01]

I think that one thing that is likely over the coming 10 days is a period of time is that energy is likely to be transferred across the pole from Siberia to Canada. When this occurs heights are likely to be lowered temporarily around the northern half of Greenland. This may appear in the models as if zonality is likely to set in - but this is not likely as it will only be a temporary feature. Any mid Atlantic height rises I suspect will be pushed eastwards. Whether this can lead to something more substantial over Scandinavia depends very much on the amount of displacement the vortex undergoes. I can't see any height rises powering into Greenland until the vortex is cleared westwards fully into the Canadian segment ( if that occurs).

Do you think this will happen by the end of december