Model Output Discussion - 5th December - 11th December

[Mark Neal.]

Certainly a interesting period of weather, and if the current storm projections keep up, we could be in for some serious trouble. Definately going to be interesting looking at the models for these stormy setups in the coming days.

[summer blizzard]

Wow, i certainly hope the storm is not as intense as forecast.

Personally i am taking in the positives.

Despite the stratosphere being at record cold levels for the time of year we have seen lows taking a path far enough south east to drag in colder air behind them.

The models on the whole look unsettled and stormy although with a small warming of the stratosphere in recent days there may be a change afoot by christmas to something more settled.

Ensembles say the current pattern stays until at least the 19th.

[Iceberg]

A little bit based on the Thursday to Friday show:

A detailed analysis from a pro would be helpful but looking through the models and ENS there is almost universal support for the low to develop from the 15C temp differential and an entry point into a mad west/east Jetstream on Wed evening, the system is then carried along the 180mph jet straight into the middle of the UK. The Jet then peaks under the system at upto 200mph.

This is bit akin to putting a wheel on a treadmill and then turning the treadmill upto burning speed. The wheel will then obviously be turning very fast, with the faster the treadmill the faster the will goes.

The very strong support for the system's development looks rock solid to me given the above, at T120 the models by and large do not suffer from JS positioning, there are a few differences but IMO the zone of uncertainty is for the centre to be from the M4 to the Scottish Boarders, it's difficult to see it being much out of this range given the JS flow. With the favourite path over N.Wales, Pennines and exiting east just north of the Humber.

Ireland looks to be in trouble IMHO as it will experience the developmental stage of the LP system.

Given the above we can start to look at likely wind scenario's I would favour a pressure of around the 940mb mark, with a declining chance down to 930mb.

So purely IMO based on the percentage charts given to hurricanes at T120 and below.

>960mb less than 5%

960mb-950mb 15%

950mb-940mb 50%

940mb-930mb 20%

<930mb <10%

For peak sustained winds (not including winds reached on mountain tops).

<40mph less than 2%

40-60mph 15%

60-80mph 30%

80-100mph 30%

>100mph 22%

For peak winds again not including winds reached on mountain tops.

<40mph less than 1%

40-60mph 10%

60-80mph 20%

80-100mph 40%

>100mph 30%

Look out as this stands a very good chance of being a once a life time event so it needs to be taken deadly seriously.

[Iceberg]

I am in no indicating what might be being indicated by saying that both GFS and Meto take Thurs/Fri storm across the UK as a symetrical warm core system.

It is interesting to note though that symetrical warm core systems can be cyclonic in nature as well as tropical.

What is does show IMHO is the likelyhood of it's development and the chances of the stronger winds reaching the surface.

Edited December 11, 2011 by Iceberg

[Weather-history]

The only positive and its a small positive is that the Thursday/Friday storm is going to be at its worst for most parts overnight. Should be less disruption, traffic wise and fewer casualties with less people out and about. If this was during the day, it could be another 25th January 1990 toll. Friday morning could be chaos, though but at least people will be at home as oppose to trying to get home from work in the middle of that.

[tinybill]

GFS - 18z(just jumping ahead to thursday)

Just incredible,

cold air pulled down after the storm would have the potential for sleet/snow depending on track/intensity

batten down again!!!

[Nick F]

One thing's for sure, it looks like another major storm will hit parts of the British Isles later in the week - most likely the northern half, but the exact timing of its arrival and its track are still too far off in timescale to be sure that its worst effects will be felt in the early hours of Friday, though lets hope that is the case if the current wind speed predictions come true!

Be interesting to see what the T+120 fax for 12z Friday comes up with later this evening.

[snow drift]

batten down again!!!

Half a page of the thread to say "batten down again"!!!!!

Yes, the timing at the moment is overnight but as this is still sometime away, it could easily be bought forward or delayed by a few hours.

Edited December 11, 2011 by snow drift

[VillagePlank]

In the south-east we have Tues 00z to deal with, first,

with gusts expected to be about 45-70mph. Again at night-time. However, with damage caused by the odd rouge 70mph gust, we can expect trees down, and the like, later on in the week by the deeper storm as a consequence.

The winds early on Fri in the SE are much more likely to be during the morning rush-hour as the really damaging stuff moves away from the the central UK.

with gusts in the 55-80mph range.

Edited December 11, 2011 by Boar Wrinklestorm

[iceaxe]

can not beleive people are talking like they are .its still 4 days out which is FI.there was a storm shown by the models 2 weeks ago which according to some posters was going to produce blizzards for scotland.yet it just disappeared from the models completely.in fact all we got was heavy wintery showers in northern england.comments like yorkshire is gone and storm of the century are wrong at this point in time.

[I remember Atlantic 252]

weekend northerly toppler due, probably come to nothing again for southern areas, window of snow opportunity, at the moment, (my area) fri evening upto sunday evening, but by next friday window probably 6 hours at best

[VillagePlank]

can not beleive people are talking like they are .its still 4 days out which is FI.there was a storm shown by the models 2 weeks ago which according to some posters was going to produce blizzards for scotland.yet it just disappeared from the models completely.in fact all we got was heavy wintery showers in northern england.comments like yorkshire is gone and storm of the century are wrong at this point in time.

Well, I'd say FI is where the ensemble runs widely diverge.

This isn't the case, here,

with synpotic level divergence occuring around the 18th - which covers both stormy periods - you can see visually because the std-dev parameters (green lines) start going in different directions with the top one increasing, and the bottom one decreasing meaning that the 95% agreement over ensembles is rapidly decreasing. Of course, there is scope for change, but change is more likely than not to be on the detail not the wider scale synoptic pattern.

Edited December 11, 2011 by Boar Wrinklestorm

[martinj2]

can not beleive people are talking like they are .its still 4 days out which is FI.there was a storm shown by the models 2 weeks ago which according to some posters was going to produce blizzards for scotland.yet it just disappeared from the models completely.in fact all we got was heavy wintery showers in northern england.comments like yorkshire is gone and storm of the century are wrong at this point in time.

Yup........and a secondary low was going to develop, move down the North Sea and flood Holland!

[Jayces]

can not beleive people are talking like they are .its still 4 days out which is FI.there was a storm shown by the models 2 weeks ago which according to some posters was going to produce blizzards for scotland.yet it just disappeared from the models completely.in fact all we got was heavy wintery showers in northern england.comments like yorkshire is gone and storm of the century are wrong at this point in time.

From reading these forums over the years I think where people's opinion of F1 differs is where there is less or no agreement on models.

There have been a few references to storms suddenly disappearing in the past but I think in those cases they hadn't been shown consistently on all models in the same place and were more likely rogue runs or a rogue model showing something that wasn't anywhere else.

The Meto have had warnings up for Mon / Tue since yesterday I think so they believe something is likely and will no doub t be putting warnings up for Friday soon too.

I believe it's not a case of if these storms will happen but when, where and intensity in the UK for both of them are the only questions now.

[Aaron]

The course and intensity of the low can and more than likely will change between now and Friday.

But, that doesn't mean we should completely write off this storm because it is 4/5 days away, that is not FI territory!

Edited December 11, 2011 by Aaron

[chilly milly]

I would really appreciate some input from one of the more seasoned forecasters on here regarding this storm on Friday. I am feeling increasingly anxious about what is likely to come and this feeling is not helped by the posts about armageddon etc. I am being told that we will know nothing until nearer the time and then being told that it's bound to happen as it's constantly being modelled. What do we truly, honestly know at this point?

[VillagePlank]

I would really appreciate some input from one of the more seasoned forecasters on here regarding this storm on Friday. I am feeling increasingly anxious about what is likely to come and this feeling is not helped by the posts about armageddon etc. I am being told that we will know nothing until nearer the time and then being told that it's bound to happen as it's constantly being modelled. What do we truly, honestly know at this point?

It'd be a serious indictment on a number of models if this LP suddenly disappeared. The thing to remember is that pressure systems at the surface are a result of interactions with the upper atmosphere (approx 300hPa) Nominally, forecasting at this height is easier since one doesn't really need to worry about surface heating, day and night, local conditions etc etc.

So, if the jet-stream forecast is more or less correct, and at 4 days it should be - that is to say a strong jet-streak in an area of positive vorticity leading to deep cyclogenesis will be crossing the UK. In English - we're going to get a deep low pressure crossing the UK. This is why all of the main models broadly agree.it's easier to forecast conditions at 300hpa (or higher)

Questions: how deep does the low go? What track does the low take? The MetO, quite rightly in my opinion, are keeping quite quiet - although they already mention the word exceptional in their wind forecasts for later in the week.

I'd be gobsmacked if someone north of the M4 and south of the M 8 did not report a gust of wind, by Saturday, in excess of 80mph. The problem is, of course, that's a wide area - only closer to the time will we know where in more detail, and even then, slight perturbations could change the track on the day itself- and then, perhaps, we'll know how strong things might be - however, given experience, it's fairly odds on to see some (very) strong winds over the UK by the end of this week.

Edited December 11, 2011 by Boar Wrinklestorm

[chilly milly]

It'd be a serious indictment on a number of models if this LP suddenly disappeared.

I'd be gobsmacked if someone north of the M4 and south of the M 8 did not report a gust of wind, by Saturday, in excess of 80mph. The problem is, of course, that's a wide area - only closer to the time will we know where in more detail, and even then, slight perturbations could change the track on the day itself- and then, perhaps, we'll know how strong things might be - however, given experience, it's fairly odds on to see some (very) strong winds over the UK by the end of this week.

Thank you for this. It helps a lot. Good post.

[Bobby]

Looking through the ensembles there seems to be more going for a more southerly track and still very intense. Some pretty scary scenarios being modeled for the South which of course is not as used to severe windstorms. Look at these monsters:

[TEITS]

can not beleive people are talking like they are .its still 4 days out which is FI.there was a storm shown by the models 2 weeks ago which according to some posters was going to produce blizzards for scotland.yet it just disappeared from the models completely.in fact all we got was heavy wintery showers in northern england.comments like yorkshire is gone and storm of the century are wrong at this point in time.

This storm might be 4 days away but the models have been very consistent with this. The current output is very concerning and in my opinion its just a case of fine tuning the detail of where this storm will hit and how deep this low will be. At the moment I really do fear for the members in Ireland and N England but I wouldn't rule out this storm being further S affecting the Midlands/S England.

[DeepSnow]

^^ with the charts from Barb are we still looking at 70mph+ wind gusts in the south?

Edited December 11, 2011 by DeepSnow

[Jimmyh]

looking at the models this will i think be a countrywide storm. The storm force winds will be strong everywhere on Friday. 950 at the centre and even 980 out to the edges accross the whole of the country. I haved been model watching for a few years now and i can say i have never seen a model chart like this at 4 days out.

This is in my eyes no way a F/I. let us all hope that the storm hits at night otherwise we could be looking at the Jan 1990 storm.

I am wondering what the MO will update with by tomorrow

[OldMetMan]

Given that the models are still sticking to the Friday storm, perhaps it's worth considering this forecast in an historical context, compared to other major storms in the past.

In my experience, lows coming from the forecast direction that are deepening rapidly have always curved to the left, so from this point on I would expect the projected path to take a more NW route and take the strongest winds further north.

Of course, the one major exception to this was the October 1987 storm, but that was a rapidly developing secondary low, not like the Friday one.

On the other hand, there is the famous Burns Day storm in 1990, but on that occasion the low came in from the west and the south of the country got hit worst. I also recall a major storm in January 1976, when I was weather observing for the Met Office, and I clocked the highest gust at the station I was at, of 82Kts. That again was a low coming in from the west.

Everything depends on where the major deepening occurs for this predicted low. At this point, I'd say the models are looking feasible. But we have to keep firmly in mind that this is an extreme event being forecast - and a LOT can change in the meantime.

[casparjack]

I am wondering what the MO will update with by tomorrow

I think they'll say it's going to be very windy on Thursday night and Friday!!

[snow drift]

looking at the models this will i think be a countrywide storm. The storm force winds will be strong everywhere on Friday. 950 at the centre and even 980 out to the edges accross the whole of the country. I haved been model watching for a few years now and i can say i have never seen a model chart like this at 4 days out.

This is in my eyes no way a F/I. let us all hope that the storm hits at night otherwise we could be looking at the Jan 1990 storm.

I am wondering what the MO will update with by tomorrow

Initaly Yellow, Orange later. Red when they have a better idea of where it will hit and the areas that would take most of the impact.

I would say that the yellow and then orange will be UK wide though.