Away from the squabbling this is what interests me.

We certainly could be looking at a major widespread storm in the next 7 to 10 days as it is becoming a recurring theme on recent output.

Also flooding problems look likely again next week.

Yes, the PFJ could become even stronger and further south bringing the heavier rain to the s of the UK.  But it could also drive a more +NAO and higher latitude euro ridge to settle nw Europe down or, for winter searchers, a mid Atlantic ridge and given the neg AO still predicted for that time, there is the sniff of a Greenland/gricelandic block mid month. 

the sinking south of the mean jet by Arctic height rises this side of the pole to be located persistently through n Iberia delivering us on the cold side looks a forlorn hope for the time being. 

this a  repost  by fergie  

  7 minutes ago, fergieweather said:

Eastern Scotland remains the *key* concern over weekend into start of next week - some worrying totals there across upslopes in a strong SE'ly flow, beneath a large-scale gravity wave - with a currently 50% PROB of this area seeing around 180mm across a 2-3 day period.

Elsewhere, certainly some potential in areas such as parts of the SW and S Wales for cumulative issues combining either fluvial or surface water localised flooding. However, the key difference looking ahead is how possible impacts shift from the SSW/SW-facing upslopes hammered in the recent repetitive events (notably SW Scotland; Cumbria; parts of Wales and NI), more to SE'ly-facing ones.  

Further into January, whilst we see no sign of the Dec-style Tm-sourced, very high Theta-w conveyors and exceptional mildness returning, there is nonetheless continued +ve anomalies for PPN in longer-range suites, albeit with rather mixed signals by/after mid-month (around bias of cyclonicity nationwide, versus spells of greater anticylonicity at least in the south). However, even without the high moisture-loading that characterised December's scary events, the ongoing antecedent situation (sodden ground) means further flooding issues remain very likely, with heightened sensitivities even to otherwise modest rainfall amounts.  Add to that a greater chance in January (versus Dec) for some passing/temporary spells of wintry hazards (mostly in N/NE), and it may become a month where yet again, forecasts are festooned with all-too-frequent NSWWS and EA warnings of varying scope and severity. Not great.

Ties in nicely with the current MetO further outlook 

I know that Darren doesn't like ensemble mean charts but I think they have a role to play sometimes, particularly if you look at the spread charts as well.

The ECM enesmble run for London from the 00z:

http://www.weathercast.co.uk/services/ensemble-forecast.html

Shows a significant cluster delivering a cold spell around 10th-12th January, that's days 10-12.  Sufficent to drag the mean maxima down to 5C and minima to 3C

The 500hPa mean and spread charts for the Northern Hemisphere for Day 10:

So, for London a spread of roughly plus or minus 4-5dam around a mean of 532dam, which translates to 500-1,000hPa thickness of around 526 at the lower end to 534 at the upper end.

I guess the Steve Muir easterly is pretty much off now, with the Atlantic winning. 

Yes, I for one,  won't be mocking the prediction,  but it seems as though bar one GFS run,  it has gone the other way toward Atlantic domination if anything.... 

Well its not a surprise that it went one way, stalemate for so long is imo unrealistic, its just a shame it went in that direction. 

Still likely to be some snow for the extreme north, actually the NASA GEO5 model sends a polar low (arctic hurricane) over the northern isles.

I know this is pointless as the chance of this cold spell is almost zero now, with the Atlantic ploughing through. However this ensemble nearly succeeds in bringing cold, and I note the primary difference is the position of the centre of the low over the UK which is about 30 miles further south. The ensembles work on the principle of applying small perturbations but we know that from the runs a few days ago that it wouldn't have taken much to put us in a cold spell, now it probably takes more than the small perturbations of the ensembles but not that much more. 

Has anyone noticed, on a different note, a trend for height rise over greenland? That could potentially come to something, maybe a northerly after 180 hours?

Indeed. Sometimes small differences in the grand scheme of things will lead to huge changes in the small geographical area that is the UK.

Like you & others have noted, the turd in the chocolate cake in this instance has been the inability of lows to slide SE'wards into mainland Europe. I don't have enough knowledge to know what the reason for this has been (especially when very knowledgeable people gave detailed explanations of why undercutting should happen), but would love there to be a sort of post mortem on how this potential cold spell has disappeared into more autumn (for most of the UK)

Quite right I don't - they're useless. Worse than useless, in fact, as people are wont to misinterpret them.

Okay, something's not quite right there.

The 500hPa height chart you have there does indeed show a mean height of 532dam for London.

The spread chart shows 8 - but 8 what? It says "500hPa geopotential height and surface level pressure" on the legend, so it can't be either of those things on their own.

Some more simple checking shows that this morning's op run has a 500hPa height of 546dam over London at 240.

http://images.meteociel.fr/im/2902/ECM1-240_oom5.GIF

The control run has 540dam at the same time.

Both are much higher than the mean+-spread/2 you mention. Clearly that "8" means something else other than 8 dam, but I'm not quite sure what (it's not standard deviations, that's for sure!)

Just checked Gavin's video update

No stratospheric warming expected

Rinse and repeat from Dec

Jan is looking much like trash for winter fans 

Looking at the clustors at 132 hours we have these:

Together forming a 40% probability. I'll just say that although the cold spell is now unlikely, the crucial moment with the rapidly lowering heights in the Atlantic is not till 120 hours, even if lowering heights over Scandinavia make things alot more difficult before then?

What can change in 120 hours? Nothing major, but how major would a change have to be to still keep the possibility of the cold spell?

Honestly I don't believe it will happen, but its a straw people can grab onto.

I do not believe this, the polar vortex is still weakening. The reason we are on the cusp of a cold spell now (even if it won't be realized) is probably a consequence of this weakening. This process is projected to continue, as we progress through January cold spells will become ever more likely.

darren, I think it means that the op is outside the spread (which is likely 20/80%). On the London ens it is pretty well an outlier for temps. 

Again this is straw clutching, I do not think a cold spell is likely, but one thing I do notice is some attempt to create a secondary low near Spain

If that develops some circulation we might get some energy into the south like we so desperately need.

Do not rule out heavy snow north of that front.

Sorry for so many posts, but I think 12Z is an upgrade, the HP is further south over scandanavia so has stronger influence, the atlantic lows are weaker and the Euro lows are further south.

I doubt the cold will win, but it might take a few hours longer to be eventually pushed away.

All that cold air advecting over Scandinavian goes straight into the Atlantic north of Shetland, all that cold air over warm seas fuels extremely rapid cyclogenesis, and is the prime spot for the formation of an arctic hurricane.

Arctic hurricanes or polar lows are warm cored systems that are smaller and weaker than tropical cyclones but are structurally similar to tropical cyclones (and their medicane cousins) and come complete with an eye wall. There is a very real risk Shetland could actually get hit by one!

It could be, but I'd have thought they would have stated the boundaries if that's the case. The fact the chart is labelled for both 500 heights and surface pressure doesn't help either!

I'll have to check over the next few runs to see whether the control fits inside that range even when it's not an outlier. Hey, I get to say "as ever, more runs are needed" for the first time in many a year!