Model Output Discussion 12hrs. 01/10/13

[chionomaniac]

Im off to work now but maybe a challenge to keep things ticking on...

 

what crucial area of the UKMO 144 shows the high is going to retrogress-~?

 

 

http://www.meteociel.fr/ukmo/runs/2013100700/UN144-21.GIF?07-07

 

S

The retrogression of the high has already begun between T+120 and T+144. But the negative tilt on the Atlantic trough alongside the reduction in vorticty further north tend to be a dead giveaway. It's a pity that we will never see the T+168 chart, as by this evening there are likely to be further changes to the modeling as no two runs at this timeframe are the same.

Edited October 7, 2013 by chionomaniac

[Captain Shortwave]

Hi Captain,

 

I disagree,  I think the Jet is diving too far south to allow what you are suggesting to happen on this frame of the output from the UKMO.  Rather because of the buckled Jet, the High will be forced to retrogress NW towards Greenland and the Low to come into the mid atlantic.  I think I see where Steve M is coming from here..

 

Thats what I see from this 144 UKMO

Hi there

In the end the retrogression is definitely an option, but I used Humberto as a clear point where tropical features can completely turn the output on it's head. I think the best thing to do is look at the day 5 and 6 charts to try to explain my reasoning here.

I admit this is a good looking chart if you want an undercut, good tilt on the low to force it underneath and that is the crucial thing, you need to separate the warm air in the high to our north and the upper ridge coming up from the Azores.

Day 6

Whilst the tilt is still there, you can see where the jet buckles there is clear forcing on the jet from the south. A new ridge is being forced north eastwards due to the low moving up the eastern seaboard and will stop any south east movement on the low and it will pretty much stall and barrel around in the north Atlantic. You might get sufficient WAA to get some weak heights over Greenland, but fundamentally for the UK you are left with low pressure to the west and a Azores based ridge to the East which results eventually in a southerly flow.

The GFS actually shows the precise consequence I was talking about, though it's almost guaranteed to be overdone, though I must stress this is a tropical forcing issue, not as of yet the GFS defaulting as actually the best retrogression attempt I've seen was the 00z GFS run as it does get some energy underneath the high before it's cut off again.

 

It's also worth noting that the GFS picked up the effects of Humberto a lot quicker than the Euro models. I would rather sit on the fence for the minute as we know full well the effects these systems can have on the Atlantic pattern.

Either way, it's teleconnectics vs tropical influences round 2 so it will be interesting to see the models flip around trying to sort out the final outcome.

Edited October 7, 2013 by Captain shortwave

[No Balls Like Snow Balls]

Hi there

In the end the retrogression is definitely an option, but I used Humberto as a clear point where tropical features can completely turn the output on it's head. I think the best thing to do is look at the day 5 and 6 charts to try to explain my reasoning here.

I admit this is a good looking chart if you want an undercut, good tilt on the low to force it underneath and that is the crucial thing, you need to separate the warm air in the high to our north and the upper ridge coming up from the Azores.

Day 6

Whilst the tilt is still there, you can see where the jet buckles there is clear forcing on the jet from the south. A new ridge is being forced north eastwards due to the low moving up the eastern seaboard and will stop any south east movement on the low and it will pretty much stall and barrel around in the north Atlantic. You might get sufficient WAA to get some weak heights over Greenland, but fundamentally for the UK you are left with low pressure to the west and a Azores based ridge to the East which results eventually in a southerly flow.

The GFS actually shows the precise consequence I was talking about, though it's almost guaranteed to be overdone, though I must stress this is a tropical forcing issue, not as of yet the GFS defaulting as actually the best retrogression attempt I've seen was the 00z GFS run as it does get some energy underneath the high before it's cut off again.

 

It's also worth noting that the GFS picked up the effects of Humberto a lot quicker than the Euro models. I would rather sit on the fence for the minute as we know full well the effects these systems can have on the Atlantic pattern.

Either way, it's teleconnectics vs tropical influences round 2 so it will be interesting to see the models flip around trying to sort out the final outcome.

 

You said in earlier post it won't now you say you prefer to sit on the fence. Come on son make your mind up. Your flip flopping like the models

[Captain Shortwave]

You said in earlier post it won't now you say you prefer to sit on the fence. Come on son make your mind up. Your flip flopping like the models

I said this mornings UKMO would not result in retrogression, but until the models get a better handle on the situation then it's best to remain on the fence, as we already know the types of lows shown weakly on the UKMO and more bullishly on the GFS can be the difference between cold conditions and a blow torch south/south westerly.

Edited October 7, 2013 by Captain shortwave

[chionomaniac]

I said this mornings UKMO would not result in retrogression, but until the models get a better handle on the situation then it's best to remain on the fence, as we already know the types of lows shown weakly on the UKMO and more bullishly on the GFS can be the difference between cold conditions and a blow torch south/south westerly.

The thing is, is that we well never get to see the 00Z T+168 UKMO so we will never know. However the signs are there for SM's theoretical exercise. If you look on meteociel and run down the times you will see the Scandi block form at T+120. By T+144 the Euro trough has elongated and is slighly more NE positioned, the lobe of vorticity and lower heights that is the Atlantic trough become detached from the main PV segment - allowing heights to rise in between and the trough becomes negatively tilted  - in itself this is a big clue as the energy crossing the Atlantic will rather split and go under the block rather than recurve and go over.

 

The UKMO could well be wrong - but it has been leading the way and has done all last winter in these type of set ups. The ECM shows retrogression of the Ridge as well whilst it diminishes in strength.

[Swave Snow]

I said this mornings UKMO would not result in retrogression, but until the models get a better handle on the situation then it's best to remain on the fence, as we already know the types of lows shown weakly on the UKMO and more bullishly on the GFS can be the difference between cold conditions and a blow torch south/south westerly.

 

Hi ,

 

Regarding the tropical element, I understand what you are thinking.  However, based on the Atlantic in general (severe lack of Hurricane development in a one worder) and how the evolution is taking place to cause our cooler weather this week I would hedge my bets on retrogression rather than a flattening of the dynamics.  The very fact that GFS didn't see this weeks Northerly plunge and given its eastwardly bias (I know you discount it above) then its what is panning out on the ECM and the UKMO which are worth more in output at this juncture.  Also it seems that over the last 3 or 4 years come to around this time of year and the GFS is not performing like it used to.  Is this because of the other background signs others have pointed to or for some other reason I honestly don't know.  But the going on in the northern regions (ie Scandinavia, Greenland and Siberia coupled with the extremely quiet Atlantic over the last few years gives a recipe for a potentially exciting winter I would bet. 

 

Somebody said we are not going to get a high over Greenland for 5 months.  But that doesn't mean it can't or won't happen.  Just that is is unlikely to happen.  

 

These exciting building blocks we are looking at right now are only that.  But its these developments that make the difference between a good chance of a long bitter winter or regular atlantic driven mild windy rainy weather.  

 

I think things just look too different and unusual for the regular patterns to develop.  Just look at the NOA it was looking sure to go positive, then over the last 4 days it has reversed its forecast big time.  If it keeps going negative we could feel the effects early to Mid November (2010 anybody?)

 

 

[smithyweather]

And when will we know we are going to see a 2010 style November???

[AWD]

And when will we know if we are going to see a 2010 style November???

In November.

[Gaz1985]

And when will we know we are going to see a 2010 style November???

 

That was a 1 in 100 year event, probably won't happen again in my lifetime.

[Mr_Pessimistic]

That was a 1 in 100 year event, probably won't happen again in my lifetime.

yes, and got nowt in my area, as always. i really am STILL getting over it.

[Yarmy]

yes, and got nowt in my area, as always. i really am STILL getting over it.

 

Yes, but we did get a ton in Dec 09 so can't complain. Anyway, looks like we'll be getting wet in EA on Thursday:

 

[DR(S)NO]

That was a 1 in 100 year event, probably won't happen again in my lifetime.

Of course,thats not to say it cant happen......else we can pencil in the forecast for November 2110 as a shoe-in!!

[Mr_Pessimistic]

Yes, but we did get a ton in Dec 09 so can't complain. Anyway, looks like we'll be getting wet in EA on Thursday:

 

 

met office comp going for a similar thing at t72:

http://www.meteociel.fr/modeles/ukmo2.php?nh=0&carte=1594&ech=72&archive=0

but i personally pay no attention to ppn maps, they vary rarely varify (imby).   also, imby i didnt get any more than two inches in 09, infact, no more than 4" at any one time in the last twenty five years!

[pad199207]

That was a 1 in 100 year event, probably won't happen again in my lifetime.

In January 2010 I remember saying these exact words, however I was gobsmacked to have it thrown back in my face in Dec 2010 when it was much more severe!

[Frosty.]

My my how things have changed....will change, the Ecm 00z ensemble mean shows the anticyclone that was supposed to bring prolonged indian summer conditions will be pulling west into the atlantic as low pressure swings southeast along with two cold fronts, behind the second front the truly cold air will dig south by midweek to bring the first chilly snap of the autumn, temps today and tomorrow remain above average, especially further south with max temps of 18-21c but by midweek we will all feel the chill with temps struggling at 10c for northern scotland and 15c across southern england with a strengthening, unsettled and progressively colder Northerly airflow making it feel colder than the above temps suggest, by thursday and friday it will be even colder, nearer 11-13c in the south, 9-11c further north, also bringing with it a lot of showers to areas exposed to the N'ly winds which is mainly the far north and down the eastern side of the uk, it will also become cold enough for the showers to turn wintry on the hills & mountains across scotland with snow across higher elevations but becoming drier across the far north of the uk during thursday as the arctic flow is cut off.

 

Later this week, the atlantic high builds back in across scotland bringing an increasingly fine and settled spell with winds falling light and overnight slight frosts with daytime temps struggling into the low teens celsius but perhaps warming up a little as time goes on, however, the southern half of the uk, especially the southeastern half of england looks like becoming very unsettled with a trough becoming the dominant feature across the southeast and down into the low countries, the ecm mean shows this trough persisting and only slowly filling in situ with the very cool unsettled weather lasting well into next week with showers and longer spells of rain but at least the initially strong winds will gradually fall light as the trough fills. High pressure across the north then extends to remaining areas with temps slowly struggling back towards average but with cold nights and a risk of slight frosts and probably an increasing risk of fog too. 

Edited October 7, 2013 by Frosty.

[BlueSkies_do_I_see]

Events l like Dec 2010 are becoming more common. I wouldn't rule out a similar cold spell in the next few years - though perhaps not quite as severe. I think another 09/10 winter is more likely.

[johnholmes]

I do think some posters are straying from the title thread-model discussion, not our views on when/if/how another month/winter like year xxxx?

There are plenty of other areas on the forum to discuss these view.

[Yarmy]

met office comp going for a similar thing at t72:

http://www.meteociel.fr/modeles/ukmo2.php?nh=0&carte=1594&ech=72&archive=0

but i personally pay no attention to ppn maps, they vary rarely varify (imby).   also, imby i didnt get any more than two inches in 09, infact, no more than 4" at any one time in the last twenty five years!

 

Surprising really, as the North of the county got several inches. I recall driving to the football and the rural areas between KL and Norwich had 10inches+. Anyway, way off topic. You're right about the ppn. A slight adjustment would just leave the fish getting wet.

[Methuselah]

Could we please try a little 'model output discussion'?

[Frosty.]

Could we please try a little 'model output discussion'?

I am

[AWD]

I may be on my own here, but I'm a little unconvinced of a return to proper unsettled conditions within the next 10 days or so, but rather favour a messy mix of "no mans land" weather, neither truly settled or unsettled.

A look at the 500mb anomaly output first still suggests modestly positive heights nearer to the UK rather than any negative height anomalies. These hovering around our west and to our east;

Whilst some operational output may suggest a stronger influence of trough activity for the east and south east of the country, a la the ECM Det, my thinking is that this may not dig so sharply W/SW and therefore not affect so much of England as the EC Det shows. A look at the London ens shows the EC Det to be one of the wetter runs between days 6 & 10, with many more members supporting something less wet;

A look at the NAEFS pressure anomaly suite at day 10 also makes very little, if anything of any trough activity over mainland Europe, with weak positive pressure anomalies over the UK, a la the 500mb anomaly output above;

We've got the trough in the Mid Atlantic by then, which is agreed upon by virtually all anomaly, ensemble and operational output, but there remains a big question mark, IMO, over how quickly and how much of an influence this will have on the UK within the next 10 days or so. I'm inclined to believe this will struggle to make inroads towards the UK in future model output.

The NWP comparison meteogram also suggests a very dry picture for the next 10 days or so;

Notice the UKMO model starting to go it's own way by 120/144 hours. Not to be presumed defective or course, that would be foolish after the last few days, but it is lonely regarding possible retrogression of the HP at this stage in time. Will it lead the way 2 times in a short space of time? Only time will tell.

Better include something from the GFS here as some people still like this model;

A lower than average rainfall forecast for the next couple of weeks there, although rainfall does increase in week 2. IMO, this is because the GFS is doing the old chestnut, being too progressive though,

That's my view anyway. Some rain is likely yes, especially in the far SE, but nothing too significant and nothing on a nationwide scale for the foreseeable future.

[phil nw.]

Not sure about Steve's full retrogression but looking, for example, at the ECM mean at T168hrs.

 

 

indicates a stalling Atlantic with a developing Siberian favoured PV location at this early stage.

 

The UK in an area of +ve height anomalies in between an Atlantic trough going nowhere fast and that low pressure further east.

It certainly will be cooling off soon around Europe and the UK with more energy going south the warmth of early October soon a memory.

 

 

Much cooler air around Europe right down to the Med and also Scandinavia/Russia- modelled for next week.

Edited October 7, 2013 by phil nw.

[Frosty.]

I wish that T+384 hours Gfs 06z op run chart was only a few days away because there is classic retrogression in action there with the mother of all cold air by late october standards bottled up and about to scream south when the high pulls further northwest. The 6z follows the ecm 0z mean with a persistent trough bringing chilly unsettled weather to the south & east, it actually lasts even longer than on the ecm ens mean but eventually, higher pressure already well established across the north by then, eventually settles the weather down. Anyway, a dramatic change on the way this week, at last it will really feel like winter is just around the corner, and if we are going to have a cold spell in november, we don't have long to wait.  

[Paul]

Jo looks ahead to the weather for the rest of the week - change on the way...

 

 

http://www.netweather.tv/index.cgi?action=news;storyid=5448;sess=

[Captain Shortwave]

Well another northerly should be coming here, whether it's a toppler or sustained northern blocking remains to be seen, but good signs for coldies here

So much for the GFS lagging behind, first one to leave the starting gate here.

Edited October 7, 2013 by Captain shortwave