Model Output Discussion 4th Dec.2013-12z onwards.

[Northern Sky]

Not much discussion yet on that GFS 12z run..... Looks a corker to me, rapid PV movement, cold, with snow shower at times for the north. Major storm for the 19th for midlands northwards (something scarily the models are starting to firm up on). Then from Boxing Day onwards the UK is blasted with Major Storms, Massive winds and enough rain to p1ss even the ducks off (those that havent been eaten over Christmas). There certainly wouldn't be a long Christmas for the forecasters or emergency services if that comes off. Strangely though even with it being in the extended timeframe its all to probably with the amount of energy and location of the PV fragments.

Yes not the greatest run for fans of high pressure! No deep or sustained cold on the horizon but plenty of exciting weather to look forward to, with some cold shots particularly for the north. Certainly a grim run were it summer but right now Iceberg I'd agree with you - it's a corker!

[Frosty.]

Chaotic & dangerous describes the Gfs 12z op run, what a rollercoaster of a run with a constant barrage of atlantic depressions swinging in from the southwest across the uk on a turbo charged jet stream, daily fluctuations of airmass which doesn't allow any type of airflow to gain a foothold before it's swept away to the east. So it means that no 2 days will be alike, one day will be heavy rain and gales, the next being colder, brighter and showery and so on and so on until the end of the run, occasional injections of polar maritime air bring the risk of snow to hilly areas, especially across the northwest of the uk and perhaps some sleet or wet snow on the leading edge of vigorous depressions as they smash across the uk on a more southerly track at times, it's a very disturbed run with severe gales, storm force winds potential, lots of heavy driving rain, squally showers and some wintryness at times, generally feeling cold due to the sheer strength of the winds for most of the time with only very brief respite between lows. There is the chance of a bit more amplification to the upstream pattern with some brief semblance of mid atlantic ridging but it can't hold with such a fired up pattern and any ridging will likely be flattened very quickly but there is wintry potential within this very unsettling pattern.

Edited December 14, 2013 by Frosty.

[Iceberg]

The system for 1 week time that has been showing at various times on the ECM and GFS is a bit misleading as the low shoots off towards northern scotland, the assumption is that the worst winds would be up north.

The detail though shows that even the SE and god forbid London would be in trouble with min 75kts at 925mb level i.e gusts of 100mph.

[Mucka]

We have known for a while the potential for a severe storm is there but pinning down the track and timing is going to be difficult.

the period around the 18th/19th has looked most likely to deliver this potential and GFS ensembles are throwing up quite a few vicious looking LP systems of which this is a sample.

 

 

Still 120h is a very long way out when trying to predict the intensity and exact track of Atlantic storms so we will see what develops.

 

UKMO 144h finally updated.

 

Edited December 14, 2013 by Mucka

[Gael_Force]

I've made a wee gif as the NH profile looks interesting in the later stages of the run. Just wondering if the split in the vortex is as a result of upper strat squeezing and stretching.

 

[TSNWK]

UKMO 12z has stumbled out. Looks pretty much the same as Gfs at 120 and 144 to my eyes and has dropped it's idea from Friday.

?

[Summer Sun]

UKMO has finally updated at t120 and t144

 

[phil nw.]

The 12z GFS run certainly shows the full force of a mobile Atlantic setup in all it's Winter glory.

The first of those vigorous wave depressions rushing up our north western coastal fringes tomorrow

driven ne by a 160mph jet streak.

 

 

 

A very mobile outlook leading up to and beyond the Christmas period with the Greenland vortex driving the Atlantic pattern.

 

A day to day watch for further deep lows needed through this period i reckon.Some short colder shots behind the cold fronts could well bring mountain snow for Scotland and some other northern heights.

 

No deep cold but plenty of interest for changeable weather with continuing risk of stormy conditions at times.

[bluearmy]

I've made a wee gif as the NH profile looks interesting in the later stages of the run. Just wondering if the split in the vortex is as a result of upper strat squeezing and stretching.

 

 

 

the split on the trop in gfs fi shouldnt be any reflection on the 10hpa pattern. if the trop is upwelling into the strat then a split may appear some time later in the upper strat (unlikely given the strength of the vortex in the middle strat). what appears to be going on in gfs fi is that the warming in the upper strat is beginning to affect the vortex at 10 hpa. thats a long way from affecting the trop. incidentally, these week 2 profiles are subject to a fair amount of change at 10 hpa. they seem to be more reliable higher up. i suspect that up until now, the vortex at 10hpa is proving stronger than the modelling predicts. a bit like the way the models are too quick to break down a block in the trop.

[Skeggy Winter Storm]

The system for 1 week time that has been showing at various times on the ECM and GFS is a bit misleading as the low shoots off towards northern scotland, the assumption is that the worst winds would be up north.The detail though shows that even the SE and god forbid London would be in trouble with min 75kts at 925mb level i.e gusts of 100mph.

That dont look good after what happened here on 5th

[Summer Sun]

Today's NAO update maintains the positive theme for the rest of this month we have hints once more of a fall as we move to January but whether its enough to go negative remains open to question

 

Edited December 14, 2013 by Summer Sun

[Iceberg]

Is London situated at the 925 hPa level?  Unless you can provide reasoning as to how the winds at that level are going to be transported into the boundary layer... Putting aside that we're discussing a system modeled a week in advance, the GFS actually projects gusts around 50-60mph range at the surface ahead the cold front.  

Hi Weather, its a highly developmental system, with strong instability, the 925 layer will be closer to the surface than in normal pressure situations and so the 75kt(sustained winds), will likely reach close to the ground at times, particularly as its a very strong cold front. Along away off i agree, but the point of the post was simply to show that the strong winds and dangerous situations will not be confined to the North of Scotland thanks to a very active cold front. Cheers

[Iceberg]

I was going to go through the ENS but stopped at the control run as it was simply a believable and very good set up in the extended range.

Its clear that the 12z suite is keener on sending the strong jet further south, although its not buckled, it only really leads to cold air coming down.

Unfortunately the boxing day storm on the control is also far to believable...

[Captain Shortwave]

Well the UKMO has moved back to the rest of the models this afternoon. As of which I will see myself out. Simply put the longwave pattern screams a rather average (temperature wise) spell of weather with above average rainfall and plenty of potential for strong winds. Some areas may fluke a white Christmas by being in the right place at the right time, but for most they will be just hoping that the big day is dry.

Good luck on the storm hunting guys n' gals 

Edited December 14, 2013 by Captain shortwave

[nick sussex]

Well the UKMO has moved back to the rest of the models this afternoon. As of which I will see myself out. Simply put the longwave pattern screams a rather average (temperature wise) spell of weather with above average rainfall and plenty of potential for strong winds. Some areas may fluke a white Christmas by being in the right place at the right time, but for most they will be just hoping that the big day is dry.

Good luck on the storm hunting guys n' gals 

Yes another false dawn from the UKMO! Once again its T144hrs when suggesting something colder implodes,I agree re Xmas Day it wouldn't be that much of a shock to see some northern areas see snow falling, as for accumulations however probably only much higher ground. Someone nuke that PV! its already overstayed its welcome.

[JK1]

goes right through the south to the north so I presume a lot of people would be affected if it was to happen of course

Edited December 14, 2013 by JK1

[Downpour]

The system for 1 week time that has been showing at various times on the ECM and GFS is a bit misleading as the low shoots off towards northern scotland, the assumption is that the worst winds would be up north.The detail though shows that even the SE and god forbid London would be in trouble with min 75kts at 925mb level i.e gusts of 100mph.

Disgusting run. I'd rather Uncle Barty settled down with a bottle of house sherry for the entire holidays than face that. Thankfully it's in FI

[Panayiotis]

An interesting mean for Thursday...but as we all know not to be taken too literally at this range!

[gottolovethisweather]

An interesting mean for Thursday...but as we all know not to be taken too literally at this range!

 

I agree and I noticed that nearer-term prospect myself. From a broad-brush summary of where we currently are, I would suggest the outlook could be conceived as follows. My status update copied below broadly covering the prospects for strong winds, some limited periods of sunshine, no permanent cold and a potential lack of Frosts due in a part to a rampaging Jetstream.

 

A few of our minds might be converted to contemplating just how much rainfall is likely to fall in places over the next seven to ten days too as the moisture-laden SW'rly flows will be well, pretty wet! A spell of very active weather with some brief polar incursions may well bring about some back-edge snowfall away from low-lying regions as we move deeper in FI.

Edited December 14, 2013 by gottolovethisweather

[bradymk]

Nice to see the 12z ECM has the development of an arctic high. Nothing too substantial but something like this is what we need to deflect the jet further south to stay north of the PFJ. A much better polar profile than previous runs and GFS.

Edited December 14, 2013 by bradythemole

[Summer Sun]

ECM once again has some very deep lows crossing north of Scotland so every chance of some Severe gales at times in the north and west

 

 

Potential for some more widespread gales at t216

 

[TootyFruity]

Hi

On the model charts how can you tell if the energy is going over the top or underneath ?

Sorry to sound stupid and it's probably really obvious .

Thanks

[Summer Sun]

It remains very unsettled on Christmas eve with some severe gales for some

 

 

A closer look at that low

 

[Swave Snow]

It remains very unsettled on Christmas eve with some severe gales for some

 

 

A closer look at that low

 

 

 

 To my mind that is part of the Vortex very close to the UK

[Frosty.]

Regular short bursts of cold air are spread throughout tonight's Ecm 12z op run along with brief milder incursions, high pressure never stands a chance but there is occasional weak ridging across the southeast which would bring temporary respite from the worst of the winds and rain but for many it's a persistently disturbed pattern with low after low sweeping across the uk and only the briefest of flat ridging separates us from the next stormy atlantic system, some wintryness will occur because there are occasional incursions of 528 dam thicknesses which means hills, especially in the north will have snow at times and slight frosts when winds briefly ease depending on  the timing of the quieter interludes.