Atlantic Storms 13th to 16th December 2011 - Part 4

[Coast]

This thread is for the Atlantic storms during the week of the 12/12/11 through to early on 16/12/11.

[VillagePlank]

Here's how Friday is forecast to happen ...

Firstly, a quick peek at it's birth. It really doesn't start out as much,

A minor, but compact ridge starts to form East of the Caribbean. This widens, and ridge starts to affect a much wider area until the ridge is quite significant, and the isobars are closing at the top peak by Tues 12z. Towards the end of this, surface conditions are changing over the West atlantic, with 950hPa heights falling,

Falling heights are often accompanied by falling pressures; this is exactly what happens with, effectively, a surface low turning into a fully fledged (but unremarkable) low pressure system,

Meanwhile, the surface heights fall low enough to be equal to those north of the polar vortex, and temperature below the polar vortex advects out, and the low pressure joins up below the jet stream to the polar vortex. In natural English, the higher temperature at this point under the jet-stream dissipates north into the vortex, and south into our newly formed low pressure effectively handing over control to the jetstream by Thurs 00z

The jetstream, by inducing positive vorticity (think spinning top rising) deepens the low pressure, and seals it into it's own system. A slight fragmentation of the jet, produces a secondary low just south of Iceland, but this is short-lived as the stronger arm of the jet-stream following immediately after conquers all in it's path,

Critical factors for forecasting are the position of the jet, the strength of the jet, and the position of the initial ridge in the Caribbean. The critical moment is how it joins the jet-stream Thurs 00z; until that point uncertainty is likely to reign, so expect model changes with regard to intensity and track - we'll only nail the details (more or less for certain) after the data is collected for Thurs 00z, and integrated into Thurs 6z GFS output!

Edited December 11, 2011 by Boar Wrinklestorm

[ZONE 51]

Taking a closer look at Monday evening/Tuesday's storm system from GFS 18z.

Surface pressure

At 1500hrs the storm just starting to show at the west side of our shores at around 964mb,

1800hrs,

tight isobars in the SW, the wind becoming very strong,

1800hrs surface wind,

Isotachs 10m(mph)

wind gusts(max could be higher then shown here)

60-65knots into the SW

at 2100hrs very tight isobars across the SE/EA

severe gales along Southern coasts,

most likely after looking at data that 50-60 inland from the south coast and 70-80mph gusts southcoast

monday night and early hours of tuesday

0000hrs surface pressure

wind in knots

-

NAE 18z next,

rainfall has the potential to cause flooding

1200hrs-1800hrs, alot of rain from this system,(below)this moving east

1-2 inches in places from monday evening to tuesday morning?

-

things calmer in the South by tuesday afternoon then we look to the next phase of potentially damaging winds,

at 0900hrs low center over the far North, at 952mb on GFS 18z,

the isobars tighten over Western and Northern areas,

on the next chart a second deep low heads towards western shores,

1200hrs

at this times gales and severe gales whipping up over the areas were shown the tight isobars

wind 10m in knots

Some areas in the West and North would have gales or severe gales

then tuesday night into wednesday that storm system moves into the North West and Northern Ireland

Edited December 12, 2011 by ElectricSnowStorm

[The PIT]

GFS has the low just effecting the southern areas of England while this mornings breakfast forecast had it tracking over Scotland so a huge difference and a huge difference for effected areas.

[Coast]

I'm going to start with a quick look at some convective charts as although the strong wind and gusts look like being the major consideration for tonight and tomorrow, I'm seeing some additional worry with potential funnel/tornado/thunderstorm or hail events.

These are all hi-res HiRLAM charts from Lightning Wizard:

Still that threat of a very strong convective gust over Sussex - this has shown up for several consecutive runs and from different sources

France is looking grim later

and look at the rain for all of us

Onto more general indicators, again this wind gust chart has been showing similar figures for several runs, sorry it only shows the corner of the UK, but currently I reckon that's where the action is (+ I can't find a solely UK based version!!!)

Again I can only find these versions of the Beaufort scale wind at 10M charts, but you get the general idea:

So around midnight for the worst of it for many of us? Lets hope it's exciting but not damaging.

[Lauren]

Forgive me as i am still a relative noob.

I see the tornado and ligthning prediction maps seem to have the highest risk on the leading edge of the storm, that is the same thing with hurricanes, yes? Will we also experience an 'eye' type thing?

All i can say is look at those isobars! I don't think i've seen them that close together in the UK for years and years.

[Coast]

Fridays potential low has now sunk South right over the Channel on the latest GFS:

But that still brings a repeat of last nights storm to the South and coastal areas in particular:

Travelling further up to Kent etc into the early hours:

France getting a real humdinger!

unbelievable if it pays out:

If this tracks slightly North in the next few days, then BAM!! goodbye roof for me. Stll early days though, lots of time for change of track, intesnity and position

MetO

ECM:

[lorenzo]

Every time I revisit the main Atlantic storm thread it grows by 2-3 pages !

In the interests of this not getting lost in the mix and to save John reposting a file.

http://forum.netweather.tv/topic/71898-atlantic-storms-13th-december-2011-onwards-part-3/page__view__findpost__p__2183788

Hopefully some of our other model discussion experts can give their call on the next 48-60 hrs...

[Coast]

I'll pop these in here from the general discussion thread. Please note that they are hot-linked like many of my chart posts so although I will endeavour to update them when new runs come out, they will eventually default to the latest runs in days and weeks to come:

Still time for change but models are coming into range now but still flip=flopping around. GFS and the MetO have the low coming up the Channel and it's back a little further North again (but still affecting parts of France) with ECM keeping it all to France. I'll take GFS in posting these windy charts for the timescale under consideration:

Sustained winds:

Gusts:

At this point, it seems the worst period is as the low exits the Channel towards The Netherlands and whips the winds around at around 0600hrs on Friday morning, but if the professionals are still refining the forecast - what do I know?!!!!!

Here's another way of looking at it from HiRLAM:

Maybe we will miss it and France will be pasted, it's all up in the air!

[Jane Louise]

New thread here and please please stay on topic. No more Met O bashing. This is purely to discuss the oncoming Atlantic storm this weekend!

Cheers!

[jpwild]

On rain today, is that the low towards teh bottom left? Just over bottom part of Ireland

Edited December 14, 2011 by jpwild

[weatherobsuk]

Its 'a' Low, but not ours..that will be coming in behind this occlusion which will be moving across the South tonight. The low people are seeing in the SW currently will bring nothing more than heavy showers and possibly the occasional strong gust, but its a decaying feature.

[jpwild]

Its 'a' Low, but not ours..that will be coming in behind this occlusion which will be moving across the South tonight. The low people are seeing in the SW currently will bring nothing more than heavy showers and possibly the occasional strong gust, but its a decaying feature.

Ah thank you. Still nice to see it the way it is on radar

[Uncle_Barty]

http://en.allmetsat.com/images/goes_sigwx_1070.php

Is that the 'leaf' just starting to form just to the left of centre (48 N 45 W-ish) in that image?

Been trying to find a WV image of that area to see if there is the potential for dry air to be injected into the rear of the system, adding fuel to the bomb, but no luck so far.

[PEMBS PIRATE]

On rain today, is that the low towards teh bottom left? Just over bottom part of Ireland

http://www.metoffice.gov.uk/weather/uk/surface_pressure.html

T+0...T+12....T+24 are tonights low................T+48 is 'the' low everyone is talking about

[Roger J Smith]

Have been looking at the situation in depth past two hours. UK Met Office caution is justified. This evolution is difficult for the models and any slight changes in set-up now to 00z could pull out the entire low from its current location rather than the bits and pieces that the models show. What has complicated the situation is this smaller-scale low presently over Ireland, inserted between the deep low from Tuesday and the developing storm north of the Azores.

Anyway, I don't see any danger signs of sudden developments around 40W but the Met Office have to keep that option open (I believe) until at least after the 00z model runs. But would have to say that the most likely track is through the Channel into Belgium, which is going to result in only moderate wind speeds for southern England and a cold rain turning to sleet or snow both at elevation and in the colder aftermath. The probability of some more energetic northward pushing track is realistically about 10% now, but 36h is a long time in storm development.

[Upgrade]

Sorry but it is relevant to talk about the Met Office in relation to these storms, as they are just a Government Department forecasting the events.

If you can't criticise a government department when you don't think they are handling things as well as you think they should, i'd say it is fair comment to be honest and it's a bit strange to say you can't comment on the met.

I rarely criticise the met but i think they deserve it in this case. They made the classic mistake which amateurs like ourselves often make - called it too early. Just shows they are human i suppose.

i won't say any more.

Edited December 14, 2011 by Upgrade

[knightrider]

Incase nobody read this on the previous thread > To be honest yes, cause right now any guess is better then giving no final verdict at all. Personally I think they should just issue warnings of extreme winds 80mph right across SE and if it dosn't come off then at least they can say something like "We apologies if our forecast has caused any inconveniance or panick but at least it was better then it being the other way around i.e; we dismissed stormy winds at the last minute then they decided to wreek havok." Just an example of how they could cover themselves by doing the sensible thing and not taking a chance of another 1987 scenario I genuinely wouldn't wish that apon them.

Ok no more MetO bashing now I promise!

[Eskimo]

Please shut up now!

[knightrider]

To the guy who mentioned about The Sun saying more extreme storms on the way, don't believe everything you read in the papers lol They just want more sales, the headline in The Daily Express earlier this week makes me laugh now when I look at the latest predictions, them saying 100mph and worst gales in 30 years. I will eat my hat if that happens!

[NickR]

The thread begins "no more MET bashing", and then within 18 mins 2 people have done just that. Are you people 14 or something?

[weatherobsuk]

http://en.allmetsat...._sigwx_1070.php

Is that the 'leaf' just starting to form just to the left of centre (48 N 45 W-ish) in that image?

Been trying to find a WV image of that area to see if there is the potential for dry air to be injected into the rear of the system, adding fuel to the bomb, but no luck so far.

Here you go, from the NOAA NHC page

http://www.ssd.noaa.gov/goes/east/natl/wv-l.jpg

[Wivenswold]

If you're going to bash government departments start with the ones who deserve it. Transport, Health, Education, Home Office, The Treasury, it's all going to the dogs. The Met Office pre-warn of the potential for a nasty storm, which developed, but was a couple of hundred miles out. Seriously, this country could do with people getting passionate about serious issues.

Anyway, where are my blinkin thunderstorms, haven't had one all week. I blame er....no-one.

[Upgrade]

The thread begins "no more MET bashing", and then within 18 mins 2 people have done just that. Are you people 14 or something?

i believe i have explained myself and have been a member of this site for 5 years. no reason why the Met should be a sacred cow, nothing abusive has been said about them, it's all been constructive.

[Purplepixii]

F.F.S. "upgrade" and "knightrider" why don't you just create your own thread about met office bashing, p*$$ off there and leave the rest of us to serious discussions!

(sorry mods, you can delete this if you like but it had to be said, I and others have wasted enough minutes of our lives over the past few nights reading the absolute bull that these 2 have spouted & they seem incapable of understanding more politely worded requests to cease & desist! )