kold weather

Also one final thing about the 06z GFS. It may not look much of a looker, but make no doubts about it is a cold set-up. Pretty much everyday from the 27th onwards has frost for most of the country under slack cool LP and daytime maxes don't look going much beyond 4-5c. Would probably give a CET for the period somewhere between 1.5-3c, which by recent standards is pretty cold. Its setting a good groundwork in its own right and helping to cool down the ground and the SSTs around our shores which will help later in the season in any further marginal events (which I'm getting a sneaky feeling there will be based on how common this pattern of diving LP's has been thus far).

GFS stuck in a holding pattern on the 06z run, with the 264hrs looking nearly identical to the 144hrs chart in terms of placement of features. At some point it will break on this run, and until that point we remain in a broadly cold pattern, though any LP that dives down like the 06z GFS is going to be mainly cold rain outside of high ground and perhaps leading edge stuff. We do keep getting a lobe of the vortex in probably the worst possible of locations that prevents any attempts at legitimate height rises near Greenland, but at the same time it prevents us from escaping the broadly colder pattern. So overall the 06z is a marked step down from the potential pattern that was present yesterday, though its still on the cold side and as long as that remains the case we could well see a shift up in the pattern. Of course, remains a realistic chance the 06z has gone off the deep end with the placement of the vortex and may well back away from it again in a few days, neither solution would be that surprising. The 06z is certainly not a throw in the bin type run, its still sets a decent groundwork.

More of an atlantic ridge rather than a Greenland high on the GFS, however the general trend is somewhat similar to the ECM at least! Its much better than the 00z GFS thats for sure and whilst its likely to topple, a fair chance we stay in a cold pattern this run. Would probably be some decent falls on higher ground on this run, possibly some leading edge stuff lower down as that LP comes down on the 06z run.

Looks like a reload type pattern, though we'll be lucky this time to get a vortex lobe quite as impressive as the one coming down. = probably a more typical wintry fare for this type of pattern. Also looks a little too far west for my taste but then I'm never much of a fan of HP formation in that part of the basin, I't too cautious! EDIT - then again its colder on the front end this time so that may make up for the less impressive upper cold pool.

Yeah, the 06z run looks a little stronger again but the trend for a lobe of the vortex to be in place over W.Greenland is still there this run, and does have some backing from GEM as well...but then agian these are the two most progressive and frankly less reliable models when it comes to blocking patterns forming. Still looks like a cold pattern is forming, but just not quite as eye wateringly good. Temperatures may well not end up too drastically different though between the different solutions.

Very true and there will be fearures that might crop up short notice, though I do have to say with regarding to a possible big event I was a touch worried yesterday because I was starting to see adjustments south. For those of us who have been around the block abit, we know that historically LP's tend to adjust southwards as time goes by. EVery single model has been slowly heading further south, even the ECM. Its now at the time point where any more minor adjustments south and its going to be a France snow event not a UK one, and I have to say that is a perfectly plausible solution at this point. Beyond that and the GFS suite has totally lost the plot with the upper high over the Atlantic, though the 06z GFS OP does look a little more reasonable this time round at least. I wouldn't be surprised if its just the GFS doing its normal wobble.

Potential is there for a significant snow spell over the next 2 weeks. 28-29th is still cold enough but uncertainty over track of any secondary low has if anything strengthened. If anyone odds of it ending up too far south have gone up However that still puts us in a good spot for a second bite down the line.

Interesting quirk on the GFS ensembles this evening, not sure if is just fluke mind you. Nearly every run that takes the LP on the 27-29th either weaker or further south towards the far S.England ends up setting up a northern block of some sort that holds at least to 300hrs. Most runs that make the LP much stronger or keep it further north ends up with the upper high toppling towards the UK fairly quickly after 240hrs. There maybe some logic in that sequence as well, as a stronger vortex will rotate more energy to its north further west (larger vortex after 28th means a bigger fujiwara effect arc) and into the zone where any developing ridge would be coming from, thereby putting any developing upper ridge under pressure both from the west and east, therefore making it smaller/weaker which will be more prone to collapse from pressure to the west. May not mean a jot down the line, but it was interesting to observe.

I suspect its the angle of approach od this low that means it takes a long time over water which moderates the temperatures upwards further, its coming down from the NW-SE direction which for plunging lows tends to be not be a great direction, you typically want a move due north-south type plunge. The fact that this set-up is cold enough snow in this type of plunging low set-up is actually not all that common in these types of set-ups and is probably due to just how vigorous the upper low remains (they normally weaken off once they head SE.) You normally in WNw/NW airflows have a strong low remaining somewhat further north. I don't expect the snow zone to be too large in width. The best case is we get a cyclonic loop, in which case somewhere close to the center of that loop will get probably a good 12-18hrs of snow (take a look at Jan 10 for an example of that in CS England) but the models have somewhat moved away from that idea. However these features are tricky to forecast and I'd rule nothing out just yet, from getting a big event like that one, to getting absolutely nothing as the low struggles to form or forms too far south in the channel.

I think in this set-up your never going to get upper temperatures much below -6/7c due to the source of the LP, unless you have a really exceptional set-up (Dec 10 comes to mind) but those are a once in 25 years type jobs. I agree that any snow that does settle may melt fairly quickly. Alot will also depend on timings of when the front arrives in your location. Those that get it overnight or IF it hangs around long enough into the following evening may well get quite abit of settling snow. For those that get it during peak daytime hours it maybe more of a struggle. However I *still* stand by that somewhere is going to get a decent snowfall out of this (10cms+) IF it forms far enough north. That would be by far my bigger concern, not whether its cold enough.

Yeah I think the biggest risk is going to be if we set-up a longer term west based -ve NAO, something not too dissimilar to the ECM. These can be a nightmare to dislodge because you are in a decent -ve AO pattern at that point and those LP trains can be tricky to shove sufficiently far away (they tend to be quite chunky Lp's from experience size wise) to bring the cold back down into our shores. Of course when that does happen that typically tends to be when very major snow event can happen of course. Hopefully we get the usal eastward adjustments as we move closer to the timeframe to allow us to reduce that threat. A half way house would be ok eventually and probably give us a shot at a snow event beforehand, but a real legitimate west based -ve is going to be wasting quite considerable amount of ideal time.

So I still see nothing to yet sway me from the 28-29th snow event possiblity, the only concern again is exactly where any secondary depression forms. It IS possible it forms too far south, indeed history tells us these things do tend to adjust south so we need to be aware of that when looking at the output. If there is a band over England, especially on the northern flank if the secondary depression forms, then there will be snowfall, perhaps quite alot...BUT its a very large if still this far out.

Yep this is something I've been increasingly talking about over the last few days, I think the set-up is cold enough the real unknown to me is simply where the secondary low forms, etc. Could easily swing into the channel instead and totally miss us, equally could still develop further north than currently progged, etc. However if the set-up comes off anything remotely like the 00z models suggests, then there will be a decent snow event for *some*.

Yeah I think that far out is very much a watching brief for the moment, there isn't huge deep cold pool to tap into so we are going to need a fairly decent connection to get the proper cold air down. A LP over the top ironically may not be the worst thing around 240hrs providing we can get another pulse northwards of the ridge afterwards, as that may help to introduce colder air onto our section of the arctic which will help enhance any northerly. A long way off though and more than decent chance of snowfall on the 28-29th for some, perhaps considerable amounts locally.

I'm increasingly confident of a snow band somewhere in the southern half of trhe country over the 28-29th period. Some uncertainties still with the exact evolution and subtle changes in the development of any secondary low will make the difference between a quick dusting in a fairly small area to a 15-20cms type dumping (though again limited in geographical extent). Literally every model I've seen thus far this morning has an area of snow somewhere in the southern half of the country, so its 100% cold enough. The biggest uncertainty in my mind is whether or not the secondary low forms as has been advertised this morning, still probably 1-2 days too soon to be real confident on that, and indeed on the location.

GFS ensembles in general are much flatter on this suite out to 180hrs it has to be said many runs won't make it this set of ensembles. Doesn't mean all that much though on its own, we will need to see if other suites also continue this adjustment and if it grows in strength in terms of agreement.

Interestingly despite being no where near as interesting synoptically, the 18z GFS is actually both colder and snowier out to 300hrs. However its synoptically a pretty ugly run compared to what we've been seeing in the past day and the set-up will probably default towards standard fare. Good ole GFS always finds a way in the end

I suspect there will end up being an area that ends up close to the circulation of the low pressure that gets *hammerd* - somewhere will cope a good 10-20cms from this set-up providing there is actually an active front present. The 18z GFS is about the worst case scenario as it happens at this point for the 28-29th. Its because it makes keeps a fairly broad slack LP and only makes a secondary depression quite late. Compare that to the ICON run which forms a secondary low far earlier which helps to wrap in a small area of colder air into the flow and strengthens the fronts as well. Hence why that run has a decent snow event, be it some what limited in geographical scope. However there may well be some rain further removed from the core of the LP in any milder section of the airflow, that is true.

No, and to be fair this solution was present on the 12z GFS ensembles as well so its not exactly come out of nowhere. The control run for example had something not too different from it. Still was a decent run that time as well.

I don't want to jinx it because the GFS will find a way, but I can't see any realisitic way from 228hrs position that we can avoid getting that cold air right over our shores. Biggest risk his run is it just topples down towards us. In itself that may still end up being usable if the upstream pattern works in our favour. Quite the difference though from previous runs. Shows there is alot of uncertainty with this pattern still.

We will have to wait and see. The evolution out to 225hrs though is very different from any of the GFS runs today thus far which have all followed a broadly similar pattern. i'm curious where it will end up as there is alot more energy riding up the western side of the ridging. May end up with a HP much closer to our shores instead this run. We will see. Still looks good btw, just different.

I'll wager you might end up being quite surprised just how much snow we will wrangle out of set-up like the one we are seeing from the 28-29th. Alot will depend on LP/frontal placement, but somewhere could get lucky if it sets up well and does a small cyclonic loop around the bigger LP flow. If that happens somewhere will end up with 15-20cms. It won't be a large area of snow, but could be quite decent fall if we get lucky.

Yes definately looking better out to 192hrs, also a slightly better looking tilt as well to the upper high that exerts more SE pressure upon the LP that is heading towards us. Weaker, but better placed.

Haha I'm basically like "next slide please!" Yeah I'm comparing whats going on upstream. Nothing yet to suggest we won't get a very pretty FI, of course there is a big difference between a pretty looking FI and one that will actually give us the goods in real terms! There have been stunning ensemble runs synoptically, until you see the 0c isotherm well north of the Midlands.

Worth noting the ICON typically is overly conservative when it comes to snowfall in these types of situations (it showed nothing till the day back in early December) so the fact we have the ICON on board showing snowfall is hugely telling to me that we will be on the right side of marginal Don't get too hung up on the exact positon of the lows/fronts, they will shift around probably quite drastically from run to run, these secondary low features are nightmares to forecast. But from an IMBY point of view, I give the ICON a thumbs up, its close enough to my area to provide interest. I said a while back that the 27-29th period interested me, and the GFS ensembles have done a half way decent job in the super extended range flagging up the possiblity, though it was way overboard with the blocking in the end.