Probably it'll hit by July

Well, still an absence of blocking at high latitudes, which is consistent and not that surprising.  I still hold to the view that the effects of the SSW aren’t appearing yet, although there’s still that chance that it won’t have a major effect.

Midmonth onwards (somewhere from the 14th to the 17th) is what the GFS has been suggesting for the past 4 or 5 days. That timescale has not changed.

Before then, as you say, largely anticyclonic with perhaps a few wintry showers in some eastern parts on Tues/Wed. The ECMWF data show a gradual trend downwards midmonth too but with less data available it is less obvious how well this is supported. It may come to nothing but the GFS has certainly been persistent about some form of cold midmonth. Whether that is a short sharp blast or something more prolonged is very uncertain. Overall the trend from both ECM and GFS seems to be for colder air starting to sink south after the ongoing anticyclonic spell.

None of these comments from me are forecasts (Tues/Wed aside) as I think we all know what can happen with our weather, they are just observations of what the charts show and have shown. 

According to forecasters monthly forecasts there is not much evidence on this SSW  taking effect this month. even tho certain people are saying end of the month. the SSW might happen in FEB just like last year that's if it does happen.. any time after FEB is pretty pointless. still the models are showing cold blips... high dry and cold seems to be the theme for next few days or so...

Is it though Michael ? 

Here is the GEFS at 288 (mid month) and the % chance of sub -10c air.

Its a fairly pointless chart at this range but so is assuming the cold will develop.

http://www.meteociel.fr/modeles/gefs_cartes.php?ech=288&code=&mode=29&carte=0&proba=1

GFS not GEFS.

The lower resolution ensemble members with the various starting tweaks have not had the consensus shown by the vast majority of operational runs or GFSP runs. I have not really discussed the ensemble data from the GEFS suite very much because of that lack of consensus. I wouldn’t pay much attention to individual op runs at that range but the trend and consistency in that trend is much more informative. One cold or mild op run at day 10 to 15 days out means little in my experience, retreated scenarios over a number odays in op runs is a different matter entirely.

As for a cold spell, who knows. I’m not making a forecast just showing the clear trend and consistency in the GFS op and GFSP data. 

http://www.weersite.net/?actueel&ensemble&ecmwfpluim 

The SSW has already happened. 

And the charts are showing northern blocking - just mostly not in the right place to bring any cold to the UK, which when you consider that NW Europe takes up less than 10% of the circumference of the planet shouldn’t really surprise anyone. 

My view from the public’s perception is that there will be a brief chilly spell next week from a glancing northerly followed by a cold high settling over the UK. The papers will claim that this is the beast from the east they have been predicting, and then it will gradually turn milder and more unsettled into mid month as the high sinks, with a chance of some renewed retrogression bringing some more meaningful cold at the end of the month and into Feb. 

Just my thoughts based on the overall trends in the models. 

I'd agree with this. Looks like the models have resolved about the next week now. After this it is a bit of a guessing game at the moment, but I'm hopeful with the continued medium range signal for colder weather from the meto that it does eventually arrive!

Any bets on the upcoming 06z GFS op or GFSP (or both I suppose) having a potent northerly of some variety between the 13th and 17th of January?

I'd just like to correct this - at Christmas it was the week 5 and 6 charts which were amazing. It has moved foward a couple of weeks, which makes sense as it's now a couple of weeks later. It's not always in la-la land in other words.

Fair enough , its becoming crunch time soon if the models don't show significant changes soon then this will be a bust. Crucial timing 20th January onwards.  

It's definitely getting closer those are the best week 3/4 ecm 46 dayer charts I've seen all winter.

We will all soon find out I'm nervously hopeful they're onto something. 

Most frustrating period of model watching - for cold lovers, all we are promised is some jam tomorrow, never today.

We have had an SSW, we are in the middle of zonal wind reversal in the strat, the PV is all over the shop, yet we are stuck in the same old rut as though none of that had taken place. We keep being told, "be patient", but at this rate, we will be waiting until April and then we will get snow just when we least want it.

P.S. the latest GFS run - look at the current synoptics and those at t+144 - virtually identical with our limpet HP refusing to move anywhere in the right direction (north and west or north and east).

we miss out again on the cold air

Yes, the SSW has happened, but - measured in terms of wind reversal in the stratosphere - only 2-3 days ago.

I don't see any Northern blocking yet?  A high pressure cell over the North Pole, splitting the PV, but that isn't high latitude blocking. As you know, mid-latitude block we've had parked over us for a few days isn't SSW related.

I agree about next week: a brief chilly spell as the LP dives south, then renewed high pressure building in from the west. The exact track and intensity of the LP still isn't nailed and that will dictate just how much cold air gets advected our way.

Given the flux at the moment I'd say a slowly sinking high was one possibility but not certain. Indeed, the charts seem to be pointing at the high relaxing away to the south-west rather than sinking. By then we're over a week ahead and the charts will be giving us a slightly better glimpse into the second half of January.

Does appear that northerly shots are becoming frequent though - so take that how you want. Alot different than the last 2 weeks of December anyway.

Do we?

Look at the blues and purples still to our north @ 180? I know this will retrogress a little but heights still remain low over the north so it looks like a brief colder snap mid month and that's it with more sustained cold reserved until end of Jan:

Call me obtuse but I would have thought that a HP cell over the North Pole is about as high latitude as northern blocking can get? 

The problem is that it's too high latitude, and allows a huge lobe of the PV to sit to its south but still to the north of Europe, leaving us in westerlies at least for a time:

Now that's starting to look more like what we need.