Possible severe Atlantic storm Wednesday 18th December 2013 onwards

[Thermohaline Conveyor]

The frontal wave/bulge undergoing development  (Wed/Thu) storm system is currently located between Newfoundland and the Southern tip of Greenland.  What's noticeable is the extremely powerful jet-streak ejecting out of the Eastern US Seaboard, giving an immense amount of fuel to this wave in infancy.  Tracking from the 06Z GFS this morning is more inline with the ECM with a 'left' bias due to the rate of explosive cyclogenisis and the phasing.  All in all a very intense system, that will bring a spell of violent winds to the Western Isles especially (Isle of Lewis/Uist) etc.

 

The squeeze in the isobars around the South Western flanks of the developing storm at T+42 (Thu 00Z) across the Western Isles is cause for concern with Storm Force 10 or Violent Storm 11 highly likely, gusting would be in the region of 80mph+

 

As for the run-up to Christmas, further bands of heavy rain and gales are expected, with very low geopotential beginning to assert further South towards England and Wales for Christmas Day and beyond.  As the thickness at 500mb decreases and cooling aloft becomes apparent, so to will the thunder shower coverage increase exponentially, expect some lively weather around Christmas.

 

The big day itself is throwing up quite a few possibilities, it's a case of wet and windy or wet and stormy.  Plenty to monitor!

[Coast]

The frontal wave/bulge undergoing development  (Wed/Thu) storm system is currently located between Newfoundland and the Southern tip of Greenland.  What's noticeable is the extremely powerful jet-streak ejecting out of the Eastern US Seaboard, giving an immense amount of fuel to this wave in infancy. 

 

 

 

 

 

[EML Network]

HOLY MOO, That Low pressure system is the size of Europe !!!

 

[Paul]

Latest forecast for the week ahead from Jo Farrow here - stormy weather on the way..

 

https://vimeo.com/82081999

[Thermohaline Conveyor]

^ Nice resume Thermo - certainly plenty of meat left on the bone for the UK and not just the usual scraps! Certainly a higher chance of perhaps something more wintry further north at times too, wouldn't take much for this risk to sink further south in such a fast moving set-up - in a word - volatile!

I bet forecasters are a bit detracted from the festive shopping et al good excuse anyway lol.

 

Absolutely, and with the geopotential thickness falling well below DAM520<, you can bet your bottom dollar that the temporal coverage of convective driven wintriness increases in scope too.  It's a very volatile synoptic set-up right now.  More akin to the Christmas/New Year synoptic's I grew up with, before the strange ones of recent years ie. Reverse zonality etc.  I won't be surprised to see a few more forced linear squall lines either, especially with the jet-streak intensity, the massive cooling aloft and the very strong 850mb flow.  Interesting times indeed!

[Summer Sun]

Snow warning issued now for NW Scotland

 

Issued at: 1140 on Tue 17 Dec 2013

 

Valid from: 0600 on Thu 19 Dec 2013

 

Valid to: 1200 on Fri 20 Dec 2013

 

Heavy showers, likely a mix of sleet and hail on coasts and snow inland, will push in on strong to gale force westerly winds from early on Thursday morning through to late Friday morning. Accumulations of 10-20 cm are possible over higher ground and with strong winds some drifting is likely along with blizzard conditions at times. At lower levels 5 cm of snow is possible in places. With these showers there is also the potential for icy stretches to form on the roads. The public should be aware of potential minor disruption due to the snow and ice.

 

Chief Forecaster's assessment

 

Following a low pressure system on Wednesday cold air will be pulled into Scotland from the west. Frequent showers will feed into Scotland on strong to gale force westerly winds. These showers will continue through Thursday and Friday morning before dying out from the west ahead of a new low pressure system developing in the Atlantic.

 

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=warnings&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1387497600&regionName=uk

 

We also have 2 warnings for strong winds

 

Issued at: 1137 on Tue 17 Dec 2013

 

Valid from: 1500 on Wed 18 Dec 2013

 

Valid to: 2359 on Wed 18 Dec 2013

 

Heavy rain and gales will affect South and West Wales, South West England and some southern coastal counties of England on Wednesday evening. Gusts will reach 50 to 60 mph quite widely, with 70 mph gusts likely in exposed coastal areas. Heavy rain may also cause some localised flooding across parts of Wales and South West England. The rain will clear and strongest winds will ease by the early hours of Thursday morning. The public should be aware of the potential for minor disruption.

 

Chief Forecaster's assessment

 

A deep area of low pressure will pass close to North West Scotland during Wednesday evening, extending bands of heavy rain and gales across many areas from Wednesday afternoon into Thursday morning. Strongest gusts are likely in coastal areas exposed to the southerly winds. Heaviest rain will be on high ground in the west, with the potential for both river and surface water flooding.

 

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=warnings&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1387497600&regionName=uk

 

Issued at: 1055 on Mon 16 Dec 2013

 

Valid from: 2105 on Wed 18 Dec 2013

 

Valid to: 1200 on Thu 19 Dec 2013

 

Severe gale force winds are likely to affect parts of Northern Ireland, central and northern Scotland on Wednesday night and early on Thursday; gusts may exceed 80 mph locally. The wind will lead to large waves with some coastal over-topping possible. In addition, persistent heavy rain will quickly clear from Scotland leaving squally wintry showers. The public should be aware of the potential for disruption from this combination of weather events. This is an update to the Alert to bring the start time forward into Wednesday evening, by which point the strong winds may already be affecting Northern Ireland.

 

Chief Forecaster's assessment

 

A rapidly deepening area of low pressure will pass close to the NW of Scotland during Thursday morning. There is some uncertainty about the depth and track of this low, but the high gusts, in combination with heavy rain and some coastal flooding, have potential to bring disruption. In the wake of the main storm (beyond the period of this warning), a regime of wintry showers will bring an increased risk of hill snowfall and icy roads. Given the potential for a significant winter storm the public should continue to monitor the Met Office website for updates to this warning.

 

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=warnings&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1387497600&regionName=uk

[Eero Hermann]

[Mapantz]

I may well head out with the trusty Kestrel anemometer tomorrow night, as I did on the St Jude storm, although there's no warnings for down here, there's easily potential for gusts in excess of 70mph, certainly right up my street, so to speak ..

 

Just as a I say that, warnings are issued for the south west;

 

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=map&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1387324800

Edited December 17, 2013 by Mapantz

[Summer Sun]

Another warning issued this time for rain for just about all western parts of the UK

 

Issued at: 1216 on Tue 17 Dec 2013

 

Valid from: 1500 on Fri 20 Dec 2013

 

Valid to: 1500 on Sat 21 Dec 2013

 

An area of heavy, rain along with strong to gale force winds, is expected to cross the UK from Friday afternoon and through Saturday morning. This will bring some locally large accumulations, particularly on hills, and following previous wet weather is likely to lead to some localised flooding across western parts of Scotland, Wales and England. The public should be aware of the potential for disruption from flooding and keep up to date with latest forecasts and warnings from the Met Office, Environment Agency and Scottish Environment Protection Agency.

 

Chief Forecaster's assessment

 

A deep low pressure system is expected to move across the Atlantic later this week, arriving into western parts of the UK on Friday afternoon. With mild air and strong winds some large rainfall totals are possible, particularly over high ground in the west of Scotland, England and Wales. There remains some uncertainty around this system and this alert is likely to be updated in the coming days.

 

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=warnings&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1387497600&regionName=uk

[Coast]

Latest from Liam Dutton's blog:

 

Fast-moving jet stream to bring gales, heavy rain and flood risk this week

 

Following a recent spell of settled weather, this week will see low pressure after low pressure arrive on our shores, bringing heavy rain and gales. Whilst it’s not unusual to have stormy weather at this time of year, the coming week and beyond is looking very lively – especially for north western parts of the UK. This change is due to the speed and position of the jet stream – the fast-moving ribbon of air five miles up that determines the weather that we experience at the surface.

 

Not only is it moving further southwards this week, it is also going to pick up in speed, reaching 220mph at 30,000ft – about as fast as it gets. The reason for this super-charged jet stream is very cold Arctic air from Canada colliding with tropical air from the Caribbean. As the jet stream is driven by temperature contrasts, such a large difference in temperature over a relatively short distance is making it particularly powerful. This jet stream is then acting as a conveyor belt for developing deep areas of low pressure and catapulting them towards us – one after another. 

 

Heavy rain and flood risk

 

The next five days are looking wet for much of the UK, but western areas are likely to see the greatest amount of rainfall. Here, 20-40mm of rain is expected widely, with the hills of Wales and western parts of Scotland and England having as much as 50-100mm. River levels can respond quickly to heavy rainfall during the winter months, as water swiftly runs off the land and into river catchments – potentially causing flooding. Whilst the latest Environment Agency three-day flood forecast doesn’t highlight a particular flood risk at the moment, I expect this to change as the week progresses.

 

Very strong winds

 

Another notable feature of the weather this week will be the strength of the wind. As deep areas of low pressure pass to the north west of the UK, gales or even severe gales are likely. Of particular concern is a nasty storm that passes just to the north west of the UK later on Wednesday and into Thursday. Whilst there is still some uncertainty about the exact path of the storm and the strength of the winds it will deliver, the potential is there for damage and disruption for Northern Ireland, along with northern and western parts of Scotland. The Met Office has issued a warning for gusts of wind of 60-70mph, with a few places reaching 80mph. This has the potential to bring down trees and disrupt transport. However, at the moment, with the worst of the winds expected during Wednesday night, it may well be the case that disruption may not be on the same scale as it would be if the peak winds hit during the daytime. Nevertheless, it’s one to keep a close eye on.

 

Even away from these areas, wind gusts in the range of 40-60mph are likely elsewhere, which will make for tricky travel in the run up to Christmas.

 

http://blogs.channel4.com/liam-dutton-on-weather/fastmoving-jet-stream-bring-gales-heavy-rain-flood-risk-week/5481#more-5481

Edited December 17, 2013 by Coast

[Thermohaline Conveyor]

Christmas Day - Wet & Windy/Wild?

 

MSLP pressure perturbations for the period from approx 24th until the 26th make interesting viewing.  To give a much clearer picture of the overall ensembles and the variability involved at this time frame, I've provided you all with the ensembles for based on the last 4 NCEP/GFS runs.

 

One thing that is very noticeable is the dip in MSLP around Christmas Eve and during Christmas Day.  Although the mass of perturbations across the 4 runs, when combined into one super-ensemble, look extremely messy, the overall correlation is one of decreasing mean sea level pressure as we approach the big day.  The mean drops from 1005mb to 988mb between 24th 18Z to 25th 18Z.  Other perturbations within the super-ensemble drive the central pressure even lower towards the 975mb mark.

 

 

Not a lot can be deduced from the super-ensemble in terms of specific tracking or general evolution of any particular low, but one thing that is clear is the presence of low pressure around the Christmas period.  ECM/GFS both indicate that low pressure will be in control during the big day, with varying degrees of spatial coverage and severity.

 

As for the latest 06Z GM (Global Model) GFS, it's clear by looking at the operational run that it is has a 'low' pressure bias against the rest of the perturbation within the ensemble pack.  For example, the operational indicates a low pressure system tracking across England/Wales on Christmas Eve/Day around 972mb, whereas a majority of the perturbations/members within the ensemble suite would prefer an average of 988mb with the general spread highly deviant and messy.

 

One can conclude that although low pressure is likely during Christmas, an extreme storm system is unlikely, at least across Central England, where the ensembles were projected for.  It could be that after viewing the Scotland ensembles, MSLP perturbations are better correlated with a more dramatic lowering than further South, suggestive of a more Northerly tracking low or no secondary low.  One would therefore prefer the evolution of the ECM00Z, whereby significantly low pressure sits to the West of Northern Scotland during festivities, but the whole country under the influence of low pressure associated with this powerful baroclinic region.

 

Unless the ensembles dramatically change (which lets face it is possible), Southern areas would be windy and possibly wet and Northern areas are at quite a high risk of seeing severe gales.

 

We'll see!  One thing is for sure, pressure will be low, and it will be very unsettled.

[Bobby]

...

Edited December 17, 2013 by Bobby

[Bobby]

Lots of shear tomorrow, should be a very active cold front with torrentrial rain and maybe some squalls?

 

Edited December 17, 2013 by Bobby

[Bobby]

ECM showing sustained violent storm force to hurricane force winds for the Western Isles. 90mph+ gusts? The storm showing a depth of about 948mb.

[gottolovethisweather]

Christmas Day - Wet & Windy/Wild?

 

MSLP pressure perturbations for the period from approx 24th until the 26th make interesting viewing.  To give a much clearer picture of the overall ensembles and the variability involved at this time frame, I've provided you all with the ensembles for based on the last 4 NCEP/GFS runs.

 

One thing that is very noticeable is the dip in MSLP around Christmas Eve and during Christmas Day.  Although the mass of perturbations across the 4 runs, when combined into one super-ensemble, look extremely messy, the overall correlation is one of decreasing mean sea level pressure as we approach the big day.  The mean drops from 1005mb to 988mb between 24th 18Z to 25th 18Z.  Other perturbations within the super-ensemble drive the central pressure even lower towards the 975mb mark.

 

pressure.gif

 

Not a lot can be deduced from the super-ensemble in terms of specific tracking or general evolution of any particular low, but one thing that is clear is the presence of low pressure around the Christmas period.  ECM/GFS both indicate that low pressure will be in control during the big day, with varying degrees of spatial coverage and severity.

 

As for the latest 06Z GM (Global Model) GFS, it's clear by looking at the operational run that it is has a 'low' pressure bias against the rest of the perturbation within the ensemble pack.  For example, the operational indicates a low pressure system tracking across England/Wales on Christmas Eve/Day around 972mb, whereas a majority of the perturbations/members within the ensemble suite would prefer an average of 988mb with the general spread highly deviant and messy.

 

One can conclude that although low pressure is likely during Christmas, an extreme storm system is unlikely, at least across Central England, where the ensembles were projected for.  It could be that after viewing the Scotland ensembles, MSLP perturbations are better correlated with a more dramatic lowering than further South, suggestive of a more Northerly tracking low or no secondary low.  One would therefore prefer the evolution of the ECM00Z, whereby significantly low pressure sits to the West of Northern Scotland during festivities, but the whole country under the influence of low pressure associated with this powerful baroclinic region.

 

Unless the ensembles dramatically change (which lets face it is possible), Southern areas would be windy and possibly wet and Northern areas are at quite a high risk of seeing severe gales.

 

We'll see!  One thing is for sure, pressure will be low, and it will be very unsettled.

 

Thanks for these wonderful analyses on the near-term and mid-term prospects, whilst it's all conjecture at this stage, I'm especially interested as to what may develop post-Christmas Day too, with Boxing Day possibly favouring a day for the white stuff behind the main event. Let's say I'm watching the Jet with eagle eyes.

Edited December 17, 2013 by gottolovethisweather

[be cause]

Latest forecast for the week ahead from Jo Farrow here - stormy weather on the way..

 

https://vimeo.com/82081999

Sadly since Vimeo got involved I cannot watch these forecasts ..froze after 'hello'

Edited December 17, 2013 by be cause

[Thermohaline Conveyor]

Thanks for these wonderful analyses on the near-term and mid-term prospects, whilst it's all conjecture at this stage, I'm especially interested as to what may develop post-Christmas Day too, with Boxing Day possibly favouring a day for the white stuff behind the main event. Let's say I'm watching the Jet with eagle eyes.

 

 

NCEP (GFS) Global comparison with the ECM (European Framework) is interesting.

 

The main issue between the two models around 23rd to 25th December appears to be timing and developments of two lows, with ECM running a low around 23rd into the 24th and GFS a little later.  The second low is vastly different in terms of intensity at around 11m/s and Christmas Eve for ECM and 15m/s for GFS later into Christmas.  Over 4 runs GFS was average 988mb minimum across the Midlands, much more inline with the lower wind-speed perturbations aligned to the ECM.  ECM wins at the moment, unlikely to be the exact synoptic showing on both ECM/GFS but not too dissimilar with a wet and windy picture.  Looking at the 2mT ensembles ECM/GFS comparative mean for London, the overall trend is a cooling one from after Christmas Day.

[knightrider]

I can't believe that no warnings have been issued covering London & SE yet when most of the MetO and NetWeather forecasts predict gusts of 50-60mph tomorrow evening and a more prolonged spell of 50mph+ gusts through Friday night and the majority of Saturday! 

[Coast]

I can't believe that no warnings have been issued covering London & SE yet when most of the MetO and NetWeather forecasts predict gusts of 50-60mph tomorrow evening and a more prolonged spell of 50mph+ gusts through Friday night and the majority of Saturday! 

 

I suspect we might see an update from the Met O tomorrow late morning as they do show this:

 

[Matty M]

NAE ups the ante for NI and Scotland.

 

[gottolovethisweather]

I can't believe that no warnings have been issued covering London & SE yet when most of the MetO and NetWeather forecasts predict gusts of 50-60mph tomorrow evening and a more prolonged spell of 50mph+ gusts through Friday night and the majority of Saturday! 

 

Worth noting the peak wind gusts only occur within a two to three hour timeframe, either side of that shouldn't be anywhere worthy of a warning. For my patch, based on the output posted by Coast earlier, the main event is from something like 6pm to 8pm, but still a case of watch this space! I imagine.

[Zenarcher]

Slight downgrade on the wind speeds from the 12z GFS still very strong though mean speeds between 50 to 65mph across the West coasts of Ireland and Scotland. The GFS has overall made the low slightly not as deep as the previous runs.

Edited December 17, 2013 by weathermaster

[Thermohaline Conveyor]

Worth noting the peak wind gusts only occur within a two to three hour timeframe, either side of that shouldn't be anywhere worthy of a warning. For my patch, based on the output posted by Coast earlier, the main event is from something like 6pm to 8pm, but still a case of watch this space! I imagine.

 

Especially if its associated with a squall type forced line, likely to be even less than a few hours.

[knightrider]

Worth noting the peak wind gusts only occur within a two to three hour timeframe, either side of that shouldn't be anywhere worthy of a warning. For my patch, based on the output posted by Coast earlier, the main event is from something like 6pm to 8pm, but still a case of watch this space! I imagine.

Just because something is short lived doesn't mean it isn't worth issuing warnings for, a lot of the most potent and damaging storms only last 2 or 3 hours max, it's also worth noting that Friday/Saturday's storm seems to produce a more prolonged spell of strong winds, I wouldn't be surprised to see warnings issued from Thursday afternoon onwards for that once the initial focus of tomorrow's storm has passed.

[knightrider]

Especially if its associated with a squall type forced line, likely to be even less than a few hours.

That's rather like what happened with St' Jude the really intense spell of winds only lasted about half an hour as the sting jet effect took over and the low pressure swung out into the north-sea yet they gave warnings about that storm days and days in advance, makes you wonder now whether they where that worthwhile, saying that people where caught out by it and killed as trees came down so in hindsight I guess the warnings where rightly issued, just seems strange how the MetO and the media seem a lot less concerned with this storm despite the predicted winds being arguably stronger!