nick sussex

I think people need to stop worrying and wait and see if we can get agreement at 120hrs. The models can't even agree on the shortwave at that timeframe. The shortwave shown later around 168hrs to the west will have to go se and this may bring some snow on its northern flank depending on the track. Bear in mind the GFS bias in terms of overblowing these types of developments. The ECM takes this as a weak feature and it becomes absorbed by the main troughing over Europe. I think an early key detail is how far s and e that troughing sets up over mainland Europe, you want this far enough away so that if it deepens you still stay on the colder side of it.

Thats a good point KW. This troughing could become slow moving and so its preferable to get this se of the UK, especially in case it deepens. You'd think though given the strength of the ridge to the north it should place enough forcing to eventually shift it. Of course though better to have that higher margin for error.

I wonder if any of the GEFS ensembles will show that piece of the PV making a direct hit on the UK! Given the set up if we get the right retrogression and jet angle it could happen.

OMG I'm going to have to move it from my cannon fodder model section! Yes our Aussie friend may have just trumped the rest.

In the higher resolution the GFS 18hrs looks very good. Although it might not excite people as much as the ECM this evolution would lead to a longer lasting cold spell. The key here is that you maintain high pressure to the nw as the pattern retrogresses. In terms of the uncertainty regarding troughing over Europe this is unlikely to be sorted out for a while as theres a relatively short distance between milder conditions and colder air to the north. So even just small adjustments either way can make quite a difference, although any troughing should edge se with time anyway.

NOAA mention yet again the poor run to run continuity amongst the operational output which is why they've gone with the ECM ensemble mean in the 6 to 10 day outlook. Interestingly they also mention a persistent negative NAO , additionally they're a bit wary of the ensemble solutions in the extended outlook as the big differences between members maybe giving a false ensemble mean view of the pattern flattening out upstream.

This is a better tool than looking at the operational outputs in FI. For those who have been following GP's posts thats more inline with the expected pattern than tonights ECM operational output. Theres still a good chance of some colder uppers into the UK with some snow before retrogression so if things fall right you get the best of both worlds. For longevity you do need to see that type of pattern, historically all the best cold spells have a fluidity to the blocking with Greenland high, some flattening of the ridge with an easterly on the southern flank then back to Greenland.

Yes this is the way to go for a longer cold spell, the ECM looks wonderful for a time but we can still get something similar without the concerns about the jet rolling over the top afterwards. I'm not trying to spoil anyones fun in here but just pointing out that theres more than one way to get the sledge in action.

I almost refrained from making that post for fear of seeming like a misery! There are ways to get a cold funnel of air into the UK on the southern flank of high pressure and get to retrogression with snowmen intact! I really don't see how that ECM could get to a Greenland block unless that is we have a Hollywood scriptwriter in here! Even if the upstream pattern reamplifies there will need to be a milder interlude and alot of sad netweather members seeing the last vestiges of their newly built snowmen turning into a puddle on the lawn. We need to keep high pressure further north to the west of the UK on the ECM its fast sinking. Anyway I doubt this ECM run will verify, overall the operational outputs are likely to have a lot of difficulties after 168hrs.

I'm happy to say now the ECM 216hrs/240hrs are great looking charts for snow but I think in all honesty given the big difference between this run and the earlier 00hrs the models are pretty clueless as to what happens after the initial pattern change. I don't see how you would get to a Greenland block from the 240hrs output, so a bit of a quandary here, you get early delivery of much colder air but because of the sausage shaped high the jet looks like it would end up sinking the high eventually. Theres still a way to get colder conditions and some snow before retrogression but the ECM tonight as much as it looks great later could end up in alot of washed away snowmen! Thanks ECM but no thanks!

If I'm allowed to be picky that trough over Europe is too far north, you need a se wards correction to make sure the coldest air makes a direct hit on the UK. Yes its a great looking chart but needs a tweek before it delivers.

Hard to believe that Arctic high is being modelled at the 120hrs timeframe. We spent many years on this forum where there was zero sign of this! At 144hrs theres likely to be a front lying ne/sw and some colder air heading down from the north on the ECM 144hrs, could we see some snow here on the western flank?

I think the mystery tour has just begun! Final destination? Hard to say where exactly the pattern will go, retrogression seems a good bet but before that looks a bit more interesting than yesterday. In terms of the ECM I wonder what it will do with that shortwave, i'd rather it took a more se track than dropping down to the west. Overall some very good output so far, that cross polar flow is not a frequent visitor so lets hope the models make the best of it.

Theres a certain irony to todays ECM operational run regarding the shortwave track. In this instance it becomes so amplified that we see that curve back in the jet which sends that shortwave to the sw rather than se. We do eventually see more favourable troughing developing over mainland Europe but preferably we'd want to see the shortwave head se. Thereafter it does find its way to that Greenland block and this seems to be inline with the current signals. The one thing we'd like to see is a Greenland high orientation like this mornings BOM: Here is that more oval shape and you'd likely see disturbances running sw in the flow, the ridge is far enough east to mediate against the coldest air funnelling sw to the nw. You've got a decent amount of energy in the southern arm of the jet. Now if you look at the ECM: Here the high is more aligned ne/sw even though you have that strong ridge over northern Russia historically its rare to see that troughing head se with a joining up of the Greenland block, generally the low heads more s/sw and this is where you can get into difficulties with a more western based negative NAO. We often worry about the pattern being too far east, this is often the case with northerly topplers but in this instance my concern would be with it being too far west. This might sound ultra picky and of course the ECM at 240hrs is still a good chart but I tend to view the outputs more from a what can go wrong aspect in terms of colder weather. Using this the BOM for me gets a green all systems go, the ECM an amber rating! Thats not to say that if we see a western based negative NAO that it won't trend back eastwards again but I'd rather see the higher margin for error BOM trend be the one that verifies.

Just taking this run at face value it does tie in better with the expected pattern than the earlier GFS 00hrs run. It gets to a similar place as the ECM 00hrs run at 240hrs. The uncertainty seems to be what happens in between ie the shape of troughing over Europe and whether the UK will tap into some colder uppers by way of the Arctic high ridging south before retrogression starts.

I think theres a slightly better chance of getting some colder uppers into the UK before any retrogression and this is in relation to the Arctic high ridging south. As this does so it could pull a finger of colder air sw and this could get redirected into the UK, much depends on how quickly the retrogression takes place if it does indeed verify.

Yes we only bring it out when it shows good synoptics! Normally its left festering in the cannon fodder model section! If I was in the UK and offered an outcome at 240hrs that would be it, i'd take it and run to the nearest sledge shop!

I think the BOM at 240hrs is the best case scenario with a good shape to the Greenland high. The pattern is not too far west and you'll get disturbances running sw into the UK. http://www.meteociel.fr/modeles/bome_cartes.php?&ech=240&mode=0&carte=1 The core of the high is ideally placed.

In typical model fashion now that we have got cross model agreement on the upstream phasing of those lows we now find disagreement as to where that shortwave drops south. The ECM seems resolute here with dropping it south to the west, and thats two runs in a row. The GFS has the best option in terms of cold in the higher resolution and the UKMO is a halfway house. Although the ECM eventually gets low pressure into the heart of Europe it does throw alot of milder air north into Europe beforehand. I'm hoping the ECM might be wrong here but when it does this two runs in a row within 144hrs you really can't ignore it. Thereafter it develops a typical retrogression pattern with troughing developing to the east, the only thing to be wary of in these situations is not to have the pattern too far west. If we get lucky then that troughing and high combo should pull down some much colder uppers and snowfall. Indeed even in the earlier timeframe a finger of much colder uppers gets funnelled sw out of Scandi,the GFS looks better for this, the ECM has already started its retrogression and because of this any colder uppers at that point generally only skirt with the UK before being funnelled into the Continent. We should know this evening whether the other models will follow the ECM with that shortwave.

Oh did you have to remind me of that trauma! Yes it was lovely seeing all that snow fall just to the west of London! The sum total in Wimbledon where I was living at the time was a few rogue snowflakes blowing about in the wind. Grrrrrrrr! Yes thats a good example of frontal snow with not so cold uppers thanks to that lovely feed of lowish dew points off the continent.

For snow showers the general rule is around -8 uppers off a northerly, for an easterly you need minimum -6. For frontal snow you can get that with 850's just below freezing but that only really comes about when you have had much colder conditions for a length of time, Atlantic fronts moving in from the sw can produce that frontal snow with a flow ahead of the precip from east/se imparting lowish dew points. It's easier to get frontal snow on the continent simply by the fact that in many of those situations you're not dealing with any sea modification. To get really good North Sea convection the bigger temperature differential the better hence if you see sub -10 uppers across with a strong flow and live on the east coast then thats generally the time to get the sledge out! Just think of the North Sea as one of the Great Lakes in North America, with the right synoptics it can turn into a snowmaking machine.

From a purely IMBY perspective I'm liking this GFS run as it brings lots of snow to the Pyrenees and we don't end up with the unfavourable looking troughing of the ECM. Interestingly the mystery of the UKMO upstream pattern continues, its the latest at phasing those two lows and really looks like the odd one out across the output. The fax chart sticks to the raw output but I just can't see all the rest of the output being wrong and it being right especially given its recent poor performance in terms of verification.

JS it depends on the type of synoptics and how much embedded cold you have at the surface. For frontal snow you can get away with 850's just below freezing but this is more likely on the Continental landmass. I can tell you from experience of living down here that we can get snow with those values but any easterly or ne here isn't modified by any sea track. For convective snow showers off an easterly you need 850's much lower.

Lol! I'm not saying there isn't, but you can end up with something better whilst waiting for the pattern to retrogress with a few tweeks here and there. Firstly the shortwave drops se into the Continent we get some elongation to the troughing further into Europe this stops any milder air being pulled into the flow. Although we're lacking real deep cold the shallow cold surface layer delivers low temps with night time frosts, the ground cools in readiness waiting for the north/ne flow to deliver copious amounts of snow as the pattern retrogresses!

Yes it started so well and I had high hopes then it turned into mutton dressed as lamb! It looked good but a bit like one of those chocolates that look great until you bite into it and discover its one of those horrid liquer things people subject you to at Xmas! The shape of that troughing is all wrong over continental Europe, we needed to see the elongated troughing further south and east to stop that milder air being pulled into the flow. I think we're going to have to go the retrogression route to really deliver, hope I'm wrong but I just can't see any other way of advecting some deeper cold into the flow.