Some guidance showing very strong winds for Tuesday 7th into Wednesday 8th of December

[Roger J Smith]

The infamous "Daniel Defoe" storm of 1703 was on 26-27 Nov in the old Julian calendar but that would have been 7-8 December if 1703 had been using the modern Gregorian calendar.

Now the various models are showing potential for a very strong low to form either south or west of Ireland and to track northeast across parts of Ireland and/or Britain. One or two of the current GFS thirty perturbations have lows as deep as 945 mbs (see number 4 for example); the control run has the low fairly strong and moving into the south Irish Sea and across Wales into the north Midlands. Other versions have it further north like the ECM and also the UKMO currently show. The GEM and Arpege models have lost interest in the system altogether (for the time being). 

At this point it's very much of a watch rather than alert/warning situation, for some time around Tuesday night and any part of the region with some chance of seeing alert level winds. 

For a Daniel Defoe storm repeat, you would need a track across the southeast corner of Ireland into south Wales and the Midlands, with the strongest gradients shown in any models so far. So that's not overly likely but within the realm of possibility. There's probably a better than 50-50 chance of a named storm developing. 

(later edit _ GFS slowly moving the track further west into central Ireland at 00z, while the GEM has suddenly rediscovered this storm with a very strong low tracking towards west coast of Ireland by 120h). 

 

 

Edited December 3, 2021 by Roger J Smith

[Roger J Smith]

The trend in the GFS ensemble is towards southern tracks that include some fairly intense storm scenarios for parts of the UK and Ireland but some are entirely into France. The GFS operational has backed off the earlier track slightly and moved the storm more into central Ireland. The ECM has a powerful storm depicted for all parts of Ireland that apparently tracks east then southeast, catching parts of southern England before it moves into northeast France. The UKMO has a somewhat similar outcome but keeps the centre moving east. 

Almost anything could happen in this rather volatile mixture of signals, high alert is required but can't really say with much precision what region is particularly at risk from this. 

[Roger J Smith]

ICON 12z the first to reach storm time, and it has totally changed its look from a series of southern lows to the deep low approaching Ireland camp. This will be an interesting set of 12z model runs to come, perhaps bringing some consistency to what has so far been a very scattered array of guidance suggestions. With the storm now at 96 hours, we should expect a fair amount of intra-model consensus. The very latest is that the 96h ICON has a 957 mb low in Donegal Bay and the strongest gradients around Galway and Clare in west central Ireland. The run has finished now and the impacts on the UK are mostly moderate rather than strong. However I don't expect all other models to follow the track of ICON which takes the low towards southwest Scotland by 120h. Will update after seeing 12z GEM, GFS and possibly a few others in advance of the 12z ECM which should provide its soluition around 1820h. 

[Roger J Smith]

Arpege takes a moderately strong low through Ireland into southern Scotland, a bit faster than some models, would have maybe low level alert consequences for southern counties of Ireland and north Wales into Lancs. GEM somewhat stronger on a similar track later into Tuesday, but the GEM storm begins to weaken over Britain and it drifts southeast. Would be a substantial rainfall producer with moderately strong wind impacts in parts of Ireland, Wales and western England. GFS has now gone all the way to looking like the ECM did days ago, with a slow moving intense low that drifts southeast from a position west of Ireland into northwest France. Would have large wind and rain impacts for south coastal Ireland and southwest England. Lesser impacts for Wales especially north, and northwest England, than previous runs. Then the ECM continues its theme from last night and takes a deep low across Mayo-Galway into southeast Ireland. Strong winds for many parts of Ireland and western Britain. 

There's an overall theme of a weakening low after peaking in strength near Ireland, but southwest England in particular need to be on high alert for the rain and wind potentials there. Other regions not really out of the woods yet, but this is the current rather weak consensus with several outliers. Still about a 10-20 per cent chance of a basic non-event. 

[Nick F]

Fairly innocuous-looking low moving SE across S Canada this evening, bringing snow here and northern Great Lakes merges with another low just off Eastern Seaboard emerging from N Carolina early Sunday. The low then carried E over N Atlantic along warm side of jet, but the low only rapidly deepens when moves on cold side of jet on Monday approaching Ireland.

Spring tides on Monday too, so this combined with large swell generated by this very deep low could cause some coastal flooding / overtopping of sea defences along southern and western coasts exposed to the wind /  large waves.

 

[Roger J Smith]

So far the 00z models are downplaying the southeast turn that was prominent earlier, although they generally show a strong low weakening as it tries to force its way towards the blocking high, so the southeast turn becomes a rapid extinction in the North Sea. This could keep changing its look every model run cycle and who knows where it all leads? 

[Roger J Smith]

The models continue to struggle to find a consensus but most now seem to show two things, one a weakening trend beyond mid-day Tuesday, and two, a drift southeast once the low moves inland towards central Ireland. The 12z ICON is out and it still wants to take the weakened low east-northeast but it does begin to disrupt the trough dragged along with secondary lows. 

I don't trust any of this too much, there seems to be a pattern in these long drawn out model crises where the actual solution looks more like one of the early depictions than the ones you see in "reliable time frame" 48-96 hours. So maybe this goes back to a southern track and approaches the Channel after all. We shall find out soon enough. 

[Roger J Smith]

Trend on 12z models generally holding to earlier suggestions with the same range, although UKMO now further south bringing the low across the southern coastal counties of Ireland into Wales and the Midlands. Others are generally further north at least at first, some do push the low southeast as the GFS is doing on its latest operational run. There is a very slight weakening trend and in a lot of cases the models are showing Ireland taking the brunt of strong winds and a more moderate outcome for most of Britain in a weakening storm scenario. If the eventual track shifts south of Ireland though, that wouldn't be the case. 

[Nick F]

I think if we didn't have the block over Svalbard / Scandi pushing the very active jet away from the deep low as it moves into Ireland, causing to it fill thereafter, it could be a much different story - with a still deepening low crossing east over the UK rather than filling and dropping SE towards France.

Still, damaging winds for southern/western Ireland, narrow swathe of southerly gales  pushing east across UK on Tuesday associated with occluding front system moving east ahead of the low moving into Ireland. Then very strong winds wrapping around south and west of the low as it crosses Ireland Tuesday night and Wednesday morning - severe gales pushing into SW England too early Wednesday. Winds subsiding around the low as it moves SE over southern UK, but still windy with gales around coasts.

[ModestMention]

I have looked at the ECMWF and GFS ensembles for each there is one solution for gusts of 70mph on Wednesday after the initial gusts on Tuesday at 18:00.

 

 

[TwisterGirl81]

17 hours ago, Nick F said:

I think if we didn't have the block over Svalbard / Scandi pushing the very active jet away from the deep low as it moves into Ireland, causing to it fill thereafter, it could be a much different story - with a still deepening low crossing east over the UK rather than filling and dropping SE towards France.

Still, damaging winds for southern/western Ireland, narrow swathe of southerly gales  pushing east across UK on Tuesday associated with occluding front system moving east ahead of the low moving into Ireland. Then very strong winds wrapping around south and west of the low as it crosses Ireland Tuesday night and Wednesday morning - severe gales pushing into SW England too early Wednesday. Winds subsiding around the low as it moves SE over southern UK, but still windy with gales around coasts.

Typical I was looking forward to a proper storm too 

[Roger J Smith]

This discussion should probably continue in the Storm Barra thread and I would suggest locking this thread now. There are some model solutions that are far enough south that Ireland would not absorb that much energy from the storm and it could come into the southwest of England and south Wales with considerable force, but the majority of guidance now shows this being far enough north that most of the strong winds would occur in Ireland; a really strong storm moving through parts of Ireland could remain strong over the Irish Sea for north Wales and Lancs, Cumbria. I would not expect that much forecast clarity with this late-developing storm until perhaps Monday morning or even afternoon based on the Monday 12z guidance. 

[A Face like Thunder]

Well done Roger, I've watched developments with interest!