kold weather

The ensembles show that the 18z probably is up there as one of the most progressive runs in bringing the deep cold over our shores. Therefore its very much a best case sceanario. The other things gleaming thorugh the ensembles out to 180hrs, there is a really wide range of solutions out there, even at 144hrs. The mean is going to be next to useless as many are showing very different patterns. For example, some show high pressure leaning into the UK, others have HP into Greenland, others have a mid Atlantic high with LP's riding over the top. All will show the central high pressure in the Atlantic like Kasim's chart, but all have VERY different prospects for future cold. The easterly also looks at least a little cooler on some of the runs, not all of them but in the fine margins we are talking about it may bring more places into play next week.

Doesn't need to be strong LP. just needs to be elongated in a way that would eventually promote a SW type airflow. Thats what way the Para GFS goes deeper in FI as the upper blocking morphs into a very west based -ve NAO type pattern, so much so its almost not a -ve NAO anymore as a weak lobe of the PV slips into its wake. Thats a far from unlikely pattern and one that the ensembles have been constantly flagging up for some time. Very long way away still of course, just showing a possiblity!

I'm hoping that we don't end up with a quick flush out then very west based -ve NAO which resets us back to the SW airflow. IF we can avoid that, perhaps this next week is better viewed a primer event. It'll cool things down so if we do end up with a marginal set-up down the line (which in this type of evolution is possible) then it may well be the right side next time. Note the ECM 12z has quite a decent cold pool to our NE to draw upon by 240hrs. The key is we MUST not have that LP just fill out to our west. If that happens the odds of this thing collapsing rises exponentially. Over the UK or even better just to our SE will probably ensure another 10-14 days of cold from that point.

We are basically in a summer pattern which in itself is interesting. However even in the depths of summer you can still end up with large 980-990mbs low in the mid atlantic. It'd be somewhat bad luck, but it definately could happen, indeed the phase 3-4 progression of the MJO would suggest thats a real possiblity as well. Lets hope though that we maintain enough of a structual block and keep that LP to our SE that we need not worry about it.

The big fear is we end up basically in a repeat of this week set-up, but less favourable thickness/500mbs temperatures to go along with it (which might be balanced out by cooler SSTs and surface temperatures mind you). The GFS para looks a little too cold for a low coming down from that angle in my experience, and has often ran a little too cold deeper in its run, a flaw it shares with its OG in its earlier days. Both the em/Para show a similar evolution as well, so it'd be foolish to not take it seriously as a possibility. It'd also put us in a dangerous position should the NAO become too west based.

A west based -ve NAO doesn't have to necessarily be a disaster, alot really depends on just how active the Atlantic is and the start of the southerly running jet. The patter is very devoid of any major activity so its just a case of hoping that there isn't a poorly timed strong LP out in the atlantic. If its jut a weak wave train we will probably get away with a west based -ve NAO for a time.

Lets hope so Steve. Normally these types of things go eastwards over time, but it would be utterly typical if just for once the models like para GFS are right. What appears likely at this point is some sort of cut low will come SSW again, we've seen the twice already this year so its clearly a pattern that has some legs to it. We DON'T want it to our west again, otherwise we'll flush away what cold we have and reintroduce milder air from Europe, at least in terms of 850hpa profile again and again we will be looking for reintroducion of cold air, which frankly has been hard to come by as we are sadly going to find out from this relatively mild easterly.

I do think that low looks somewhat overly done, though to be fair we've already seen some pretty mean lows diving SW this month, stronger than I'd normally expect so maybe its not totally impossible? The GEM also shows what could happen if we get unlucky, ridging everywhere but the one place we don't want a upper low, just south of Greenland!

18z GFS is about as good as it can get in terms of the synoptic set-up past 144hrs. Its a shame the lower level airflow is too warm when we have that easterly, otherwise it almost certainly could have been a very impressive snowy spell. Still, the set-up from the 18z GFS is more what we want to see. As others have said, when you've got such an extreme pattern developing the models are probably going to be swinging from one extreme to the other quick rapidly given just amplified things are about to get.

Yeah there isn't settling snow of note, though thats not to say it won't be snowing by that time as Thursday does see the whole atmosphere start to cool down as lower thickness and lower uppers start to crawl down from the north. Big low coming through at 216hrs, quite rapid strengthening. Lets hope it can get far enough SE, I'm not convinced.

12z ECM at 168hrs is light years away from the 12z GFS it has to be said. Hopefully the driver low forming at 168hrs doesn't get stuck like it did on the 12z GEM which brough about a premature end to any cold set-up, and that it can get far enough south to give a length cold shot.

My worry is the upper high sets-up too far west and therefore we end up with a flabby upper low dropping south somewhere to our north-west as the PV basically starts to fall apart. That forces any nascent ridging that may try to form over the Atlantic southwards and we end up with a position seen in quite a few ensembles in recent days, with a flabby Atlantic low either to our west or north-west, higher pressure around Europe and a mean W/SW flow. You can have the most impressive upper pattern out there in the Arctic but if that sets up shop your in for a mighty struggle to dislodge it, especially with zonal winds now so low and little to shift the pattern once it sets in. In a way I'm worried the SSW is actually going to prematurely kick us out what was morphing into a great set-up. EDIT - we will likely get away with it for a time on the 12z ECM, but how long that holds?

ECM screams wintry mix to me, maybe more of snow overnight but a sleety mixture during day time. Any heavy showers turn to snow but then back to sleety stuff. In 05 and 06 we had several easterlys just like that and that was generally the way they went, snow overnight, sleety mixture during day. Very little accumulations during the day apart from at decent altitude. Suspect this is going to pan out very similar.

I'm struggling with thay paralell. Mainly because its actually strengthening a vortex lobe smack bang over the arctic between 192-240hrs. At the same time nearly all other models are doing the opposite. Suggests to me the para is underdoing the northerly extent of any attempted ridging. Either that or it score a bit a coup!

Looks quite a complex pattern, though one I have seen various times before in both historical set-ups and hypothetical setups seen in ensembles. There is a weak upper low feature that draws across Greenland around 240hrs which looks like it slams the door shut on the ridiging there and it all starts to sink southwards from that point in conjunction with that upper low that just sits and a general deepening of pressure in our section of the arctic. Its got increased support from the models in the past 24hrs, so its realistic, though we have also seen these set-ups try to pop up in cold spells before only to kicked into touch once the time draws nearer.

Kinda, its more they lift up the upper high too quickly due north, which opens the door to that LP coming into SW Europe to head N/NE which introduces the milder air. Not all are going west based, some then get the LP east of us and bring in colder air again as you can see on that ensemble. Its why actually a slightly more slack and less keen to move JP may not be the biggest problem in the medium term providing it gets there in the end of course!

Thats looking pretty close to where I'd eyeball the mean of all the 12z suite so far. The only thing I'd love to see is that LP slow down a little, even 2-3hrs later will bring the chances of accumulating snow upwards in a decent way. Also yes looking increasingly likely there will be a decent snow event for N.England.

Yeah its not going to be a huge event for London unless some of the more extreme solutions were right, and eyeballing most of the ensembles London/M4 is more or less the cut off for the heavier precip in a lot of the runs. There are some that go considerably further north and a few of those runs end up actually being rain further south. Generally speaking the higher the resolution, the more south their outcomes tend to be. Given the location of the low is probably just entering their domain of higher resolution its probably time to start putting more weight into them and the more southerly route. However what the ensembles do show is there is still a *range* of solutions, that it isn't quite clear cut despite decent OP agreement.

So looking at the GFS ensembles later, quite a few are making an attempt to push milder air into the country from the south between 192-216hrs. Broadly speaking the slower the HP is to move towards Greenland the colder they remain for longer at least at 850hpa. More progressive and faster runs (and also more northerly) runs bring in a snow-rain event around that timeframe. So it MAY be better to actually have a slower moving less aggressive upper high at least to start with, which prevents the risk of everything shooting up too fast and not getting the cold air down before we shift into a more classic west based -ve NAO pattern.

It could well do so. However if its a genuine and strong SSW then there will probably multiple attempts at northern ridging over a 30-45 day period. So what it may end up doing is allowing cold air to flood to our NE even if it means for a week the pattern reverts to something much less interesting.

Only two sets of runs, you can see them here: WWW.METEOCIEL.FR Meteociel propose de manière régulière les différents scénarios du modèle à maille fine AROME 0.025x0.025° (2.8km) de Météo-France sur la France, la Belgique, le Luxembourg, les Pays-Bas et la Suisse

The 12z GFS ensembles are quite interesting to say the least. They've shifted northwards. Still quite a wide range of difference between the models at the moment as well. Generally the OP runs from the models are all running south of their ensembles. Maybe due to higher resolution. It does seem like the higher the resolution the more south the models are taking this set-up...

Just a little heads up for those in the south: The ensembles have shifted northwards, indeed some are quite alot further north on this 12z suite... Only a couple are in the channel... Whilst we are getting into the timeframe where the ensembles don't matter as much, its interesting to see there IS still quite a range of posiblities open. Also worth noting the AROME ensembles earlier this morning also were north of its own run.

If we can get some decent development on the low coming down the west side of the UK a wrap around event certainly becomes a possiblity, especially in the far east of the SE/EA. I'm personally not too interesting from an IMBY, its going to take a heck of a wrap around to get to the point it gets this far west, however I'll be routing for it. I'll look at the GFS/GEM emsembles and see how well supported it is.

Its unfortunately shifting the blocking pattern way westwards, there is actually increasing pressur ein the arctic as the -ve AO really starts to take hold. Its IMO a somewhat realistic pattern and has been increasingly advertised on the ensembles as well. I'd be surprised if we don't get another shot after that point given just how strongly blocked the arctic is about to go....