snowking

UKMO raw continues to show the northward spread across this region of some slightly more intense precipitation, and a general slow down of the system as it moves across us

If I get some time later I’ll try and take a bit more of an in depth look after the 12z’s but this is starting to come into range of the highest resolution modelling now - EURO4 is a tiny but further North with the developing low than the ECM, so good news there but we will see how that plays out in the next 24 hours The good news is for the SE contingent that, assuming NWP has a proper grip on the overall dynamics of the system (even if not the track yet), the low is forecast to deepen as it runs East - this will mean that the further East it heads, the more we should see some Northerly curvature to the track. You can also see from the FAX this morning that as this happens, the fronts tend to wrap around the low somewhat. At the moment this means that Eastern-most parts of this area keep hold of the precipitation for a good while longer. Even if it were to dive south, the cold front moving across much of England and Wales should give everyone the chance to see at least something falling...and what happens when this frontal system starts to interact with the low when it hits our region? Lots to resolve yet, let’s hope the 12z runs take more of an ECM/Likely Euro4 track

Presumably MOGREPS must be further south in its track....I can’t make out why otherwise they would do this given the rest of the output we are privy to (with the old GFS the exception to this of course....but I highly doubt they would modify a UKMO Fax based upon the GFS det.)

Absolutely - assuming that NWP has all the parameters nailed (which it almost certainly doesn’t yet), DP’s are generally around 0-1c, so it will take some really intense precipitation to ensure snowfall I’ve seen countless times before the intensity of precipitation downgrade as we move closer to T+0, so the timing of the front occluding and the deepening of the low in the channel would be key to ensuring as much falls as snow as possible

ECM brings the system in about 9 hours earlier than the UKMO or GFSP - not great news in terms of some extra help from nocturnal cooling. We could do with it being a little bit slower - of course this is likely to change quite a lot over the next few days

Only up to +72 so it should start coming into range shortly (assuming it maintains a track that makes it interesting for us that is!)

I must say I was rather nonplussed about the UKMO 144 earlier for the same reason as what we’ve just seen with that ECM 168 - all looks a bit ICONesque to me still there will be more twists to come EDIT: I refer to short-mid term prospects when I say that - longer term the potential remains, but how long have we been saying that for now?

Bear in mind these run with a 10:1 snow to rain ratio - not often we see those sorts of ratios in the UK and especially not from a northerly....so those amounts will be massively overstated in terms of the specific scale....still some decent totals though, even if it is all just for fun at this stage

CFS is predicting the end of the DFS sale...it’s just around the corner When looking at the seasonal output from EC and GLOSEA, this always looked to be a risk, with the mean troughing a little further north and west of where we would ideally have liked - it initially looked to bring the risk of a west based -NAO, but it turns out you need to have a -NAO in place before it can become west based ? Anyway - given the fairly wild swings in lower stratospheric modelling I’ve seen in the last few runs, probably best not to take anything beyond a few days seriously as this point until we’ve seen some settling down of the pattern, because subtle nuances in downwelling there will have a huge affect on momentum in the troposphere, which is pretty much the key factor for us right now

The trouble is they can be just a hundred miles or so in size and often have a lifespan of less than 48 hours (from formation to death), so when you think about that on a regular deterministic run, maybe somewhere between 3-6 pixels...now think about how much trouble we have seen trying to model something like the shortwaves (or whatever members would like to call such features) which are preventing the link up between our Atlantic and arctic ridges at present, which are probably easily 4-5 times the size of many polar lows. And what you’re essentially trying to do is model the ingredients for such a formation, and then use that to predict the formation and the track....so... Add into the equation that in order to model uncertain situations such as the track of a polar low, you ideally want to use an ensemble suite, that’s exactly what ensembles are there for - to solve uncertainty. But of course the resolution of the ensemble runs is generally even lower, so they deal with such mesoscale features even more poorly (if they can pick up on them at all at those resolutions). So you then generally want to wait for them to come into the range of models with resolution of far less than 10km....and those sorts of models are normally only run for fairly short periods ahead. We’re probably in a much better position now given the upgrades to many global NWP’s in recent years, but then again we’ve not really had any UK centric polar lows to concentrate on for a long time, so it’s difficult to tell!

I remember an old Rob McElwee late night weatherview forecast, I think it must have been Jan 2004, and he said conditions looked ripe for polar low development and that it looked like there was one likely to form and sweep southwards....I think it was Jan 28th that most of the country saw a sudden blizzard sweep southwards and drop a few inches of snow. If I’m honest I can’t remember if that was a true polar low or if it was just a very active trough, but I remember thinking at the time, well played Rob! But that was very much the exception, otherwise they’re difficult not only to forecast from further out than a couple of days but also to predict the track of. There was another instance I can remember in the 00’s (no idea of the year) where a polar low formed very unexpectedly and swept down the eastern side of Scotland, the met office hurried out warnings for much of the eastern side of the UK, and I remember being sat on this forum tracking it, and watching as it curved westwards and ended up hitting the midlands and the westcountry just at rush hour, much to my disappointment. Very difficult beasts indeed.

Just thought I would illustrate exactly where the shortwave will appear as we get closer to T+0.... Well modelling still keen to keep systems moving NW-SE, which will always give us these shots at getting a ridge into a place conducive to UK cold given the current state of GLAAM with ridges trying to push north whenever they can. That combined with the slow draining of the vortex into the eastern hemisphere should still keep some interest in the medium range

I fear Nick is right here I must say. When I made this post on Thursday: I was starting to fear the worst and a situation we have seen a few times over the years where longer range modelling suggests a clean separation of troughing, only for it to find smaller features which it previously did not model as we get closer to T+0, preventing ridging from spreading its wings. We can of course hope this is just a wild solution from what have been some very volatile ensemble suites of late - we'll see come the 12z. But as we are into the ranges of day 4-5, you would usually be expecting to start to look to deterministic runs to use their superior resolution to decipher the likely direction. Anyway, this far from a winter is over post - as Nick says, this would essentially mean we lose a week, and given both the overall direction of travel with the persistent NW Euro trough/higher heights towards the N Atlantic, combined with big spikes in MT and GLAAM right now, an amplified pattern with cold spilling out into lower latitudes should be expected to continue right through into February. Its also worth remembering that if modelling of next week does turn out to have been incorrect, it can just as easily be incorrect with the pattern further out too and swing in our favour. It would just be a real shame if we couldn't get the party started a little bit earlier.

As last night, this remains a source of concern for me in the shorter term - there's been quite a few examples of clean separation of lower heights being modelled at extended timelines, only for smaller shortwave features to crop up the closer we get to T+0 and spoil the first bite of the cherry Fortunately, this is just the ICON, and despite what anybody might suggest on here, it still verifies poorly compared to the EC, UKMO and even the GFS - so nothing to panic about for now

Not to suggest that this would be what actually happens in reality, especially given those uppers over the North Sea, but you would imagine with higher pressure over our shores that cloud development would be somewhat limited in terms of height - and we see thus manifested in just some light streamers in the usual spots exposed to a NEly flow: This is, of course, all theoretical for now, and there are some other snow events across the NW as fronts attempt to encroach

I’m not even so concerned about individual op runs showing varying solutions, I think that’s just to be expected - we should be treating every op run as part of an overal suite of ensembles right now What concerns me right now is the separation of energy moving SE across us next week leaving that gap for heights to ridge in to, and I really doubt that will be resolved until at least the weekend - I’m with @nick sussex on this, we are in dangerous spawn of satan shortwave potential territory here....I’ll be much calmer if NWP still backs the EC/GFS solution come Sunday. But what we can take comfort from is that the overall longwave pattern will remain conducive to an amplified pattern with a NW European trough for some time it seems, so even if we miss this early opportunity, others will not be far away - let’s just hope we don’t need to rely on this and can see things work out at the first bite

Is this definitely the latest forecast? It reads differently for me: no mention there of snow to low levels most likely in the North and North West....unless I’m going completely mad and missing this?

Not particularly high resolution, but just to back up what Nick has said there - the scale there is in mm, and running the sequence this looks like total accumulated (with no taking into account of any potential melting etc - as you can see from the snowfall being shown over the sea!) but just to give you an idea EDIT: I should add, that's rainfall equivalent which has fallen as snow - so you can make your own mind up for mm:cm ratio for snow - depending on the airmass in the UK, anything from 1:2 to 1:10 is possible

I think we might see a few flakes in favoured spots (namely higher ground), but looking at the dew points: the coldest of them are behind the trough, and given the time of day I suspect we may be just the wrong side of daylight to see much in the way of wintryness apart from in any heavier bursts....we’ll see! Maybe something on the back edge closer to sea level...

Hopefully the last 24 have shown that when we have limited resolution modelling trying to cope with the physics of an unusual stratosphere setup (ie against climatology) then nothing is certain - anybody thinking off the back of the 12z GFS suite that we’re back in the game should go back and read the last 24 hours of posts and see how quickly things can change back and change again fascinating watching, but far from certain on any model suite right now

There was some discussion about this on Twitter when this article was published - essentially, NWS forecasters themselves came forward and said there was no truth to this as far as they knew https://twitter.com/everythingwx/status/1083039436257017857?s=21 And then came this from the deputy administrator of NOAA https://www.postandcourier.com/opinion/commentary/weather-prediction-still-accurate-even-during-shutdown/article_6944faba-15d3-11e9-96ea-b79ddbf38e0b.html So I think any thoughts that the government shutdown has affected GFS performance are as unfounded as the whole ‘lack of data’ fallacy we get over Christmas every year

I see @Catacol has made a similar point above but for the benefit of everyone as a reminder - Crewe, you’re hardly the first person to do this this season and is suspect you will be far from the last, but those meteociel strat charts only show temperature at 10mb - and temperature is not the indicator of where the vortex is/isn’t, you need to look at GPH for that. So, here’s where we were on the 12th: In fairness, the stratospheric high not too far from the north of Scandinavia, but certainly not a ‘direct imprint’ indicative of Scandinavian blocking. This does not, of course, mean that we won’t see a Scandinavian high in the tropospheric pattern, as we don’t always get a direct vertical downwell of the stratosphere into the troposphere, but drawing this conclusion based upon the stratospheric pattern on the 12th is I’m afraid not quite right.

Two things - 1. BBC website location forecasts (not that anybody should be paying any attention to these) are derived from the ECMWF now - presumably raw det. 2. @bluearmy that’s twice now you’ve mentioned west based negative NAO in the last 18 hours...what are you trying to do to me?! Still a very prominent risk I think given the location of troughing anomalies on seasonal modelling suites, and looking at the last couple of EC46 runs....but to put on my rose tinted aviators for a second, fortunately that risk looks to be out at week 5/6, and we still have weeks 2, 3 and 4 to get through before then - even then, it’s not impossible to get cold and snow with a west based -NAO, it just depends how much cold we could inject into any residual troughing before then Anyway, all speculation on far away modelling for now

Therein remains my only concern - we have seen on a number of occasions in recent years modelling tendency to remove heights from the Greenland locale too readily Now in all fairness, both seasonal and now weekly modelling have been fairly consistent in lower heights there until beyond mid Jan, followed by their swift removal, which we have seen happen in a number of the more memorable winter spells...but there’s still just that little voice at the back of my mind (I like to think of it as a miniature @nick sussex) telling me not to buy into it until we’re within at least 7 days. I was also interested in your views @bluearmy on weeks 5/6 on the weeklies I saw you mention - from the brief glimpse I’ve caught of week 5 and 6 from Twitter, it looked like the risk of an increasingly west based negative NAO as time went on with the core of Greenland H500 heights sucked westwards - but you get to see far more of the suite than me, so hopefully that view is incorrect?

Does anyone have a link to these? (Thanks in advanc!) In any case, the first glances at the latest EC46 look consistent with the previous update. It’s a shame we couldn’t see a quicker trop response, but the slower one certainly looks pretty promising