Absolutely, for the sake of those in the flood-hit areas of the country, if no-one else's.

If you're still lurking Steve, I have a useful suggestion:  IDJ, White Lightning and me will take you out out for a few beers....now what could we talk about

Nothing is certain, this is the NAVGEM6Z

Still, if the GFS or ECM is right, it will gradually turn colder with heights rising over greenland. And even if it doesn't as the polar vortex continues to weaken its only a matter of time before a more meridonal pattern causes cold to arrive. The month is full of potential. 

Update on the polar vortex.

There is some temporary restrengthening by 192 hours, the polar vortex in the bizarre location of the east china sea diminishes and it reforms in the Kara which is a more sensible (if not overtly typical) location.

By 240 hours it has begun weakening again, the center of the 500hpa polar vortex is still over the kara but is weaker, and the pattern is becoming increasingly wavy. 

The polar vortex splits at 300hr with a siberian part and a much weaker canadian part. Note the AO/NAO is tending negative.

The polar vortex splits again at 384hr with one part north of Scandinavia and the other in siberia, the secondary vortex over Canada completely dissipates. While this sort of thing is going on, expect many opportunities for cold to come our way. It is amazing to me that people are suggesting that we are going to have more of the same for weeks. Have people seen the charts? The jet is well to our south, a westerly wind in a polar airmass is not the same as one in a sub tropical airmass. At best the temperatures will be average and trending slightly cooler. But in the extended outlook there is a very good chance of cold.

Not much going on admittedly in the stratospheric polar vortex today, although there was some good weakening on the charts yesterday. 

I'm not entirely sure which features in particular you're referring too - there's a trough across the UK with two secondary lows and the parent low by Iceland. Another trough is to the NE of the UK and the two merge between +192 and +240.

More important for the favourable setup is the behaviour of LP in the western N. Atlantic during that time, moving NNE and driving a wedge of warm air almost due north, which supports the development of a mid-Atlantic ridge toward Greenland. It looks like it could be sufficient for maintaining that setup for a few days beyond +240 so it's a promising run in that regard.

Now what about GFS... when you have 00z and 12z runs consistently producing flatter outcomes than the 06z and 18z it suggests that the amount of amplification to the pattern is a crucial component for how the pattern evolves. ECM's been consistently in the more amplified camp, and for some reason the 06z and 18z GFS op runs have a habit of producing more amplified outcomes than the other two runs each day - a curious observation that turns up every now and then for a few days. Most of the time it's not that evident but certain situations tend to make it more so.

Based on recent MJO activity, I'm inclined to back the more amplified outcomes... but there has been a drop off in the MJO over the past few days and if that continues today I may have to adjust my expectations a bit.

GFS parallel 0Z, thetaE values.

This is not mild. In fact these sort of thetas correspond to air temperatures during the day of only about 6-8C and around a 50% chance precipitation will fall as snow rather than rain.

And at the end of high res we have this.

which if it came off would certaintly mean some cold frosty nights. Also I tend to ignore the drivvle with these dartboard lows, and when you do that the progress to cold seems to be slightly quicker than the charts are implying.

In fact, to put it another way, technically the cold spell has already started (for shetland) and I honestly do not think it is going to end there! 

I was talking about the little low at est. 500km W of the Brest Peninsula at 192. But thanks- that was a helpful reply, and encouraging.

Look at the waa over/to the west of Greenland. I appreciate it's not ideally aligned, but could this still propagate a GH?

Help me out here- I am now getting that displacement/ fragmentation/ weakening of the PV can break down the status quo with regard the persistent airstreams. What I don't understand is how you identify which of all those LPs on a chart is the PV as opposed to just a NH depression. I read the PV hangs about a lot near Baffin but how can you tell it's the PV when there's a low N of Scandinavia or over Russia, say?

There is an element of intuition about this, the most important point to understand is that the polar vortex is a large scale cold core low which becomes stronger as you go higher up in the atmosphere. This is actually the opposite to a surface low which is strongest at the surface, the most extreme example being a tropical cyclone which is so weak at upper levels its actually an anticyclone.

I point all this out because it is necessary to distinguish a surface level low from an upper cold core low, and this is why I use that particular metociel chart which shows geopotential height and 500mb temperatures. This helps me distinguish lows that are strong at the surface (low geopotential height and relatively high temperature) from lows that are stronger further up (cold and low geopotential height). So when I look for the tropospheric polar vortex I look for very low 500hpa temperatures and low geopotential heights with the understanding that the former is a necessary criterion. 

Another thing you can do is look at SLP, if the SLP and the 500mb height structure look similar (both concentric circles for example) then that is not the polar vortex. The polar vortex has concentric circles of 500mb heights but look like a weak trough at the surface (if that). 

That's clear, thanks. I'm getting a lot from this.

I'll do an example bertwhistle and I'll destroy everyones favourite myth that the polar vortex was over the UK on the 18th December 2010. It wasn't, here's how I know that.

Firstly we look at the archive chart for the 18th.

Doubtless this is impressive, but the first thing to ask. Is the vortex stronger at the surface? The answer is a resounding yes. And the structures of SLP and 500mb height look very similar. This is exactly the opposite of what we want for the polar vortex; what we really need is the lowest heights to be over a trough not the centre of the LP itself. Now, lets pan out to the NH profile.

There is one other region of very low heights. This one is far more fitting, note that the SLP is weak and disorganised at the surface and there is no well defined vortex. In fact the pressure is slightly higher in the region of lowest geopotential heights. So lets hit the nail in the coffin and look at thickness (since they don't archive 500hpa temperature, this does the job aswell).

Oh dear. The lowest thicknesses are not over the UK, but over siberia, which leads us to the conclusion that the polar vortex was never over the UK but was over siberia. 

Sorry guys myth busted!

But its still a useful way of seeing where the polar vortex is.

FYI I'm not saying the polar vortex can't go over the UK, just that it hasn't happened yet. Why do I say this? Because once, and only once, the polar vortex got that far south. In fact it was the same latitude as northern spain. That day was January 21 1985. Look at this.

Note the lowest heights are over the USA, and that the vortex is stronger higher up; note that the structures of the 500mb height and SLP are also different with the purples and blacks over the trough not the LP centre. Now lets look at thickness.

Now its true that the polar vortex is also over Siberia, but we can say without a doubt that a secondary vortex also lies over the USA, and to me the thicknesses look even lower than they are over siberia.

But this is, to my record, the only time the polar vortex has ever visited the lower latitudes (and when it did it brought record temperatures). Not even 2010 was that extreme.

I'm seeing tentative signs of amplification in the Atlantic around day 10. This could be a route to a northerly or Greenland height rises... or just a temporary ridge before it all flattens and we are back to square one.

ECM ens mean day 10. The OP and GEFS/GFS op also showing a similar idea. 

Not exactly a massive signal but something. Behind the amplification I'm also seeing a new surge of low heights across NE N America / Greenland which then moves into the Atlantic.. this makes me feel it will only be a toppler before things flatten but we'll see.

NAEFS day 11

ECM 00z ensemble for London shows the main cluster delivering a couple of days with maxima around 3C on 12th and 13th (days 10 & 11), with the Op being in the cold cluster:

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

Worth noting also that the cold weather of Jan 1985 came on the back of a generally mild December in 1984, although nowhere near as mild overall as December just gone. Other than the well-known case of Dec 1981, I can't think of any notably cold Decembers in the 1980s.

4.4C in 1982 was the lowest CET apart from '81: certainly not worth writing home about.

Classic mid 00's style toppler on the GFS12z today:

Respectfully disagree, I know it topples in low res, but the NH picture is very encouraging.

Personally I think this is a faux scandi high situation where an initial block to the east fades only to be replaced by a more robust one over greenland. 

Doesn't look so encouraging to me from a cold weather perspective - I'm talking about what the GFS shows, not what may happen:

GEM goes for a very weak jet and a completely shredded polar vortex by 240hours

The natural progression from here is a rapid height rise over Greenland with a trough coming down from the NW introducing much colder air after a brief milder interlude.  

I agree the low resolution part of the GFS is not encouraging, but this has to be weighed against the picture the other model runs are painting which is a very different story. Up to 240 hours the GFS run is promising.