kold weather

Sorry to say but profile is too warm for snow, dew points well above 0C for the SW even at that point (indeed, far SW is upto 10C!) and although it looks like it should be cold enough, there is a significant warm sector that is present with it. It does get increasingly mixed out as it moves eastwards and so snow level comes down on the backend of it and so greater chances of snow from CS England eastwards on that chart.

Once again a VERY snowy GFS para run for a fair chank of the country, even the south has decent transient events (though rain always risk, especially close to the coast for obvious reasons). Because it creates a good snow pack, the 06z para is also severely cold, max temperatures well below 0C on this run, even the south gets a solid ice day or two. Anyway, abit different from the 06z GFS op run which never makes that snowfield and so a much warmer run, especially for the south where temperatures are basically average throughout.

Totally agree BA. Of course there is always a risk we lose out, the south in particular are at real risk of things going wrong, but you have to be in the raffle to win it! Models in the long term seem to be moving in a negative way with more going along with the idea central Atlantic upper low taking over, but there is still a large amount of time for that not to occur and I'm still expecting some decen t northern blocking between 5-10th (I always did think some of the models were being too progressive bringing vit in as early as the 30th of Jan). Not to say we can't get good wedging and mid latitude ridging before that time.

Even gives me down here settled snow...I've never seen settled snow from this sort of air source, so I'm a little sceptical to say the least, but there is always a chance to break that run and if it happens to Tues-Wed then I won't complain! Looks like a decent little trough feature running from W-E though and has kind of come out of no where. That should give a hint at to what can happen with diving cyclonic LPs, little features can crop up.

I'd say that broadly its still a set of fairly cold runs, though as noted tgere really isn't many runs yet which are showing any deep cold, but that is the trade of for allowing a set-up that allows more snow attempts and as I said there are quite a lot of runs that have decent snow opportunities, especially for Midlands northwards,

Well the 18z GFS ensembles are more or less useless for trying to figure out a pattern past 120hrs to be honest and there are a lot of very different solutions! Lots of snow opportunities on a large percentage of those runs, and the cortex keeps spitting out upper lows into the Atlantic and towards W.Europe. Other than that, no real signals crop up from the ensembles! ps, a lot of those -5C type runs also have Lps quite close by as well. Deep cold is not on the table for at least the next 12 days at least, but you DON'T need deep cold in the right set-up.

Very good control run from the 18z GFS with plenty of snow opportunities for all and also just enough cold to keep things as snow for most. GFS Para is ALOT flatter of a run but there is still some decent snow chances, but we will see where it goes later in the run with regards to any ridging and blocking.

Much depends on where that data is missing from. For example that could make a difference for locations that don't get huge amounts of data anyway such as the polar regions, etc.

Ha and the run ends with my most hated enemy, the central Atlantic upper low of cold spell destroyer! Upper highs are very tame to our north this run, I'm thinking its probably underdone on this run, especially when compared with the ECM ensembles for example. Snowy run for the north/west and also the Midlands this run, little snow for the south broadly, especially the further west you go.

Very good run out to 300hrs, several marginal snow events which for most looks just about on the right side if this run was correct. As I said in the other thread, broadly snow for the Midlands north, a mixture for the south between snow and rain more likely. Worth noting though that it maybe the snow charts on the GFS are overdoing things as is highly likely to be the case on Tuesday.

Several marginal snow set-ups on the 18z runs, though they become less marginal the further north you go and also the longer into the set-up we go. Some decent snowfall likely for the Midlands north in this run though I doubt snow hangs around for to long, a snow-rain mix likely for the south with probably little settling snow bar maybe transient stuff. Upper low dropping over the UK by 240hrs, so even though upper temps are moderating, its still decently cold. BA- interestingly the cluster with the flatter pattern is still fairly snowy from what I've been looking at.

Right so just had a look through at all the ECM ensembles (though not the arctic or snow, etc...yet!) at 500mbs and some key things emerge: 1: The PV lobe over Canada remains the key driver pretty much throughout on a large percentage of the runs and there are constant lows spinning off and moving towards our general direction. I can't comment on the surface reflection but I'd say most look far south enough that most would have a good shot at frontal snow. 2: The ensembles are not really showing any agreement on where to place any northern blocking. Nearly all runs do have varying degrees of blocking, though a few are purely a response to the upper lows dropping down, but they are there. I'd say the favoured area is probably due north of us, but there are genuine Greenland blocks and a couple of strong Scandi blocks as well. Also worth noting there are a few Euro blocks as well (aka a Bartlett looking set-up) 3: The other factor that does shine is a prevalence for Azores high ridging, which probably comes as no surprise given no.1. Azores high ridges and normally shears off to the east so even though not many runs have any true Scandi highs, the response at 500mbs is still the same. It'll be interesting to see is surface pressure matches what the 500mb level shows on that one. Overall the ensembles are better than the GFS ensembles tonight, though both are full of promise for sure as we move into Feb.

Remember if we were to get a SE flow higher 850hpa temps won't be too much of an issue, though much wouyld depend on exactly how cyclonic the flow is as the more it becomes dominated by the upper low, the worse things get, especially for the south, which is always more susceptible to things going wrong from that angle without having any decent cold pooling at all levels of the atmosphere.

I realty worry if we end up setting too far west unless it really digs down far enough, because there is a fair chance your going to be dragging up warmer air from the south on the upper lows eastern flank or we never have enough cold air aloft to begin with if the flow bends. We really need a solid Scandi high for that to work and for the troughing not to become too intense (IE low pressure nort going below 995nbs I'd say, any more and its probably going to start pulling in too much warm air). P12 on the GFS ensembles shows that concern due to not having any major scandi core. On the plus side, if we do get a decent upper high in the Scandi area, it will help in terms of not needing the cold pool being as deep to still give the goods. To be fair there is are certainly some ensemble members going down that route on the GFS ensembles, ECM ensembles still going down the mid-atlantic route in the main.

Decent snow event on the 12z ECM, nothing too outrageous but certainly 2-4 inches across most areas it seems. Quite a few GFS ensembles have something similar as well at a similar time, indeed some even have a low forming on the front which really does pump up the totals. Afterwards plenty of snow showers moving into the western part of the country, especially NW England and W.Scotland. After 240hrs, LP over W.Greenland probably going to head off SE again and we will get yet another attempt to throw up a more solid ridge to the north, which IMO has a much better chance of working out.

Good NW blast coming in at 192hrs, probably cold enough for widespread snow showers, though obviously a lot more further north and west you go. Decent run so far, even if it is in the main a set-up to a cold spell coming up.

Quite a few very strong ridges from the Azores in the 00z ECM ensembles actually towards the back end. True Greenland highs are more rarer, but still a few form right at the back end (3-4th Feb). Also quite a few runs form little secondary lows around the cyclonic LP, this could be a possibility of getting some snow away from favoured spots towards the start of the following week (27-29th). Given there is decent energy in the jet at this point, wouldn't be at all surprised if little features like that crop up as we move closer to the time.

In a cyclonic flow I would think there is a high chance of little troughs and features circulating around the lows as they down, and they may not get picked up before 96hrs either. There was a time during 2003-2007 where such featureas were quite common I seem to recall, haven't had too many cyclonic northerlies since then other than the big hitters in Jan 10 and Dec 10.

Having just had a look through every 00z ECM ensemble at 500hpa thickness, I'd say the main theme is still definitely upper troughs spinning off SE. Some are a little too far west and introduce milder air, quite a few look ok, and some look amazing. But a fairly large majority are cold, some very. There are plenty of good ridging attempts from the Azores though and so that's probably the other 'trend'. PS, I think any decent northern blocking is still a fair bit away, though as n others have said repeating SE diving LPs followed by upper ridging in the Atlantic can provide a similar result.

The 12z para hasn';t yet run far enough to really establish any northern blocking or any kind, though it is a little flatter in all fairness at least through to 216hrs.

I'm actually quite impressed with some of the models as they are moving the cold forward and we never really lose the whole displacing trough situation that we currently have, though most of the models do look like they are gradually taking down colder air each time. GFS ensembles by the way are EVEN more progressive with building in the Azores high and the SE motion of the upper low....and I though that as it is the ops are a little overprogressive! PS- watch for shortwaves in this set-up, they may well end being our friend in a cyclonic troughing set-up. It was a pretty common thing to happen between 2003-2006 I seem to remember.

Yeah I was thinking this is getting faster and faster into the transition towards a cold flow, the repeat and rinse set-up now progged by the models may not be the A* grade cold and snow some are looking for, but I'd say its a solid B and with the potential for it to be pushed up further. 12z GFS never quite makes it but I think its being a little stingy with the Arctic area and high pressure, we are basically back to neutral by 300hrs, which given the amplified pattern in the pacific and also the attempts from the Azores high on the other side seems a little unrealistic to me. Once again, people really do need to forget those runs from the GFS which went bombastic, they were a once in 5-10 year type model forecast...its not realistic to compare any model run to those runs and expect the same thing.

12z GFS OP is the type of run where I'd expect plenty of troughs and features to pop up closer to the time, its a pretty cyclonic flow and these tend not to be picked up too well until day-4/5. Nothing to be unhappy about...imagine this was all that was on the horizon for the next 15 days... That pattern held for 15 days...so just a little perspective on what we are seeing guys!!

Deep FI shows the one mahor risk with this rinse and repeat set-up, that eventually one of them id going to take hold of the central Atlantic and your going to end in a SW airflow no matter how strong the northern blocking becomes. Arctic set-up isn't as good on this run either though. Still, decent length cold spell emerging... I think some have been badly spoiled by some of those runs GFS was briefly pumping out...they literally were all time great charts, one of them was in my top 5 model run in the last 15 years...and I've seen some real crazy looking runs!

Different Arctic evolution this time and the PV attempts to pull itself back together and there is no arctic high at all in place by 300hrs which is a massive difference from recent runs, though there is ridging from pacfic so maybe it will reform around 360hrs.. Not bad at all, but a little contrast compared to the very similar 00z and 06z.