PersianPaladin

T96 to T120 evolution of the Greenland-originated trough will be crucial. There is considerable room for complications here and the previous ECM run showed how things can get messy in such a complex set-up. T144 UKMO is promising, but we must remember that at that range the UKMO starts to perform poorly in comparison with the ECM. More runs needed, but we are getting very close now! There is some hope...but I would warn people from ramping just yet.

Yes, the evolution is different but essentially the same dynamics and rules apply in terms of cold-advection. I'm currently more interested in that Greenland low and to what extent it actually produces snow for the country. It might be more surprising than forecast.

Yes, the trends continue in much the same way but as I said yesterday - the set-up is precarious and highly changeable within a short time-frame. I don't know about how the different models resolve the resolution of the upper-troughing west of Greenland or over N.Canada, but I'm suspect of this pattern. I think given the record in these situations, the extent of that cold air will end up producing sufficient cyclogenesis in the N.Atlantic to erode heights over Scandi, where quite frankly we need them if we are to have any snow except the SOUTH of the country. Too many a time have we ended up with a weak block collapsing over the UK with shortwaves over the top, flurries for the far SE and the main LOW heading off south towards Italy and Greece. I predict the same to happen in this scenario.

Of course, most of those experienced on here will be highly wary of a significant cold incursion from the NE given the overall pattern indicated by the charts. Granted, everything is interconnected including all the teleconnections, stratospheric trends, tropical convection anamolies and so forth. What the experts will (among other factors) be looking for is how the polar vortex behaves, bifurcates, decays, etc in the next T144 hours. The pattern upstream is not particularly promising west of Greenland and how much warm-air is able to advect northward in order to give time for things to fall into place east of the Atlantic High is speculative. We will have to wait and see how this very cold trough from Greenland affects us from T96 onwards and its pretty much F.I. from that point. All too often we have seen steep upper temperature gradients reappear just west and SW of Greenland to weaken and bleed energy into the northern arm enough to flatten and reduce the amplification. The result is for our dear European trough to sink southwards towards Greece....

We bloody well need some rain. I'm getting concerned about the amount of brown grass around even up here in the north. Every smidgen of Atlantic shortwaves cropping up on any ensemble should get a cheer from most, frankly.

Thunder snow several times throughout the night in North Durham. No surprise given the extreme synoptics.

It's pretty clear that the planet is running a fever. The door to the Arctic freezer has been left open and it's hemorrhaging out into the northern hemisphere, producing additional winter temperature extremes elsewhere. For example I am living in Istanbul these days and ive never known a winter with such sustained mild weather. The arctic has gone crazy, there is vicious circle of feedback of evaporation, moisture build up and further ice melt from the greenhouse effect of the latent heat. These sort of extremes look set to continue and I think even the peak oil crisis won't even be enough to force a change.

There is such a thing as "heavy drizzle", you know.... Though it isn't oft-mentioned.

Just managed to prevent my house from flooding. Very heavy rain coming down, opened the front door and saw the drains in front of my drive were overflowing. Used a plank of wood to try to wash it away before it entered the front door of the house. Thankfully the rain eased, but I am angry that whoever built our drive-drainage system appears to have done a shoddy job. The neighbors' drainage is certainly not overflowed.

It's not particularly frequent here in Durham these days either. My favourite synoptic though is in spring and summer, and also in early autumn when the North Sea blows in low cloud and varying intensities of drizzle throughout a day. But this requires particular synoptics that aren't as frequent as I'd like them to be. Interestingly, I recall the days of sea fret and "haar" being fewer these days compared to a few years ago, when haar would penetrate 15 miles inland and bring an atmospheric change from hot weather to misty cool weather in the afternoon. Not seen that for a long time, and that may perhaps be as a result of large-scale increases in sea temperatures. To have a hot day interrupted by drizzle would be an atmospheric dream for me considering that I'm not right on the coast.

We've just had a heat wave, followed by storms. Now the air is much much cooler, and there is a blanket of thick stratus hanging over the hills with drizzle falling intermittently. And I love it. The fine mist falling brings out the subtle and delicate smells of the new plant growth, and walking in the nearby woods you can see how thoroughly it covers every leaf, blade of grass and flower with fine droplets as well as fine rivulets running along some sections of the wood. The drizzle is not constant, and I love how its intensities vary as it comes and goes, with curtains of droplets that fall and often with tiny droplets dancing through the air as though they were in brownian-motion. I like the ambience it creates, the light winds and the stillness associated with it. It has a comfy quality, whether you choose to walk in it or observe it from outside whilst sitting by a fire reading. I've never seen the fields look so green when it comes and is prolonged. Come, join my Drizzle Cult. I don't want to be the only member....

Of course, there are about 10 additional teleconnection patterns officially recognised by NOAA; albeit those are considered subsets of wider teleconnections within both the Atlantic and Pacific, but also including the Asian landmass, the Arctic and so on.

Personally I wouldn't mind that sort of weather. Would be a relief to the amount of colds and illnesses going around up here at least. Still, its a pretty plausible option given the persistent modelling of the PV lobe in Greenland; which will - if not somehow warmed-out by a change in general pattern - build heights in the Atlantic in an orientation that will end up bringing mild air over us.

Interesting polar-frontal modelling differences between the UK MET and ECM at T144. Notice how the Spanish low (an earlier development from the upper Greenland trough) starts to slowly become more shallow, with heights increasing slightly north of it to the west of Ireland. Why does this matter? Well, it's a sign of less energy in the southern arm of the jet, and at T144 we can see the reason why. Look at the vigorous shortwaves developing eastward from the Greenland arm of the vortex on the UK MET, in comparison with the ECM it's considerably more prominent. This is an example of the sort of uncertainty in the modelling of the polar front in the coming days, for all models.

Indeed, but as ever - the problem of too much energy in the southern arm (linked with a high amplitude upper trough from Greenland) will inevitably bring in flatter ridging from the Atlantic Azores and milder air.

T144 to T168 on the GFS gives a demonstration of the balancing-act required for the Atlantic jet-stream. We need enough amplification northward in the right location; albeit too much energy either way - and we cause an unstable ridge-trough pattern that simply won't hold our easterly synoptics in place. The short-wave circulation near northern Spain developing on the GFS in the medium time-frame originates as a break-away from an upper level trough (cold pool) near Greenland that lingers around for too long. We want it to displace much quicker to allow a more clean development of heights to our north. Given the lack of WAA in the Greenland-sector of the tropospheric vortex (though there is some ridging northward on both the GFS and ECM, but transitory) - whatever Easterly that does develop threatens to be a very short-lived affair. Forecasting the morphology and position of the PV is a global problem, and so neither the GFS and ECM are superior in this regard. Let's hope that should we get a Scandi-high established with a dry easterly, that eventually it holds for long enough while upstream conditions change and become less mobile.

High-resolution models suggest development of two mesoscale features on Thursday, one to the west of Scotland and another to the south-west of Ireland. The latter is forecast by GFS to become prominent and develop into a more developed circulatory short-wave across southern england, eventually ending up in the southern north-sea. Could produce quite a substantial amount of precipitation perhaps even up to the midlands, though marginal for the south. Feature is also visible at 700hpa:- The feature west of Scotland, which some have suggested may be a "polar low" is a "watch this space" feature and, while likely highly transient - (requiring nowcast) may give a short sharp shock of precipitation to just about anywhere along its brief path. High-Res chart:-

Again, these are small but significant differences in the modelling of the PV split/movement. Currently the GFS persists with the shortwaves jutting out eastwards from Greenland, and this in turn impacts the amplitude of the northern polar front, creating an eastward bow-curve in the northern arm exactly where we don't want it. The GFS will "get there" eventually for Euro continental cold. But it'll be the anticyclonic dry type and with not particularly cold uppers.

Words of wisdom. The GFS solution, while having edged closer and closer towards the ECM in showing the trend of height rises towards Scandi - may actually be a sign of what eventually happens in reality. The modelling of the polar vortex is proving difficult, and it will really come down to the pace of its progressive position and intensity, with the core east of central Greenland OR (as per the ECM) poleward with the East Siberian vortex ramping up. The main point however is the issue of time and progression. The signal of a vortex weakening and upper-level warming is acknowledged in both the GFS and the ECM, albeit the former is considerably slower in terms of the pace of vortex bifurcation. That time-delay is what counts, because effectively it results in shortwave-genesis eating eastwards and northwards across the Atlantic into our part of the world. While by T200 onwards the vortex weakening on the GFS does materialise, its already too late and the core of the High has been edged southwards with convection and CAA running off south towards Greece et al.

Is that for Thursday? Too far out for such mesoscale detail. Ignore it. It will literally come down to nowcasting with regard to how that unstable trough descends southward.

I'm sure you know already that the Operational Runs are at a higher resolution than the Ensembles. If there's a subtle pattern detection, then the higher-resolution the better as small differences can make a larger outcome for cold as far as this part of the world is concerned. Still, I share the view that the ECM will stop showing that easterly in the next run or so.

Any output after T120 should be considered for the bin.

The simple fact that such low thicknesses are making their way to the British Isles in the reliable time-frame is good enough news for me. It makes things more interesting from a synoptic point of view, as I'm sure many here have gotten tired of the current dominant regime. Snow or no snow, I shall be pleased to see more energy and vigour from such cold cyclogenesis.

Yes, but you have to consider the lag-time with respect to temperature in the oceans. Look at the higher-res November and December temps over the respective weeks:- http://www.ospo.noaa.gov/Products/ocean/sst/anomaly/2016.html

Most of the warmer global temperatures are in the oceans and thus that impacts us in the UK given we're an island at the butt-end of all that extra energy supplied to the polar front. Cold anomalies off Greenland (ice melt?) and much warmer + anomalies south of Newfoundland make for a considerably disrupted jet pattern.