snowking

Whilst that immediate signal in our locale at that snapshot is not the most appealing (although I have quite enjoyed the dry and sunny element this week I must say), if you’re looking for something to help nuke that great big purple blob then that’s a pretty decent Wave 2 precursor pattern - Russian high, Aleutian low.

Just to back this up further, in my tiny part of Hertfordshire we had pushing on for 4 inches of snow from this event too - again just a further emphasis on ignoring precipitation forecasts at such range

Kasim come on, I appreciate you’re commenting at face value on the exact precipitation output shown in this single deterministic run, but you’ve been here long enough to know how poor modelling of precipitation is at such range under such conditions. ——— This next part is not aimed at you because I appreciate you try to provide a face value overview direct from modelling. But I do think in general these forums in the morning might provide psychologists with the best possible data source they could have for the effects of sleep deprivation. Nothing has changed from where we were yesterday. Deterministic runs are still just picking scenarios at random from the range offered in the ensemble suites over the last few days. Usually at the sort of ranges we’re talking you would start to err towards the view that deterministic runs, with their superior resolution, should be getting a handle on things. But this is such a difficult setup to compute, far from the usual west - east flow one would expect locally (never mind globally) that I don’t think the deterministic runs are any more use to us right now than the rest of their respective suites. And whilst it’s a fun exercise in imagination, there is absolutely no use in looking at any form of precipitation chart beyond (if I’m being really generous) 90 hours other than for a brief fanciful glance if you really want to torture yourself. Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5006518

Kasim come on, I appreciate you’re commenting at face value on the exact precipitation output shown in this single deterministic run, but you’ve been here long enough to know how poor modelling of precipitation is at such range under such conditions. ——— This next part is not aimed at you because I appreciate you try to provide a face value overview direct from modelling. But I do think in general these forums in the morning might provide psychologists with the best possible data source they could have for the effects of sleep deprivation. Nothing has changed from where we were yesterday. Deterministic runs are still just picking scenarios at random from the range offered in the ensemble suites over the last few days. Usually at the sort of ranges we’re talking you would start to err towards the view that deterministic runs, with their superior resolution, should be getting a handle on things. But this is such a difficult setup to compute, far from the usual west - east flow one would expect locally (never mind globally) that I don’t think the deterministic runs are any more use to us right now than the rest of their respective suites. And whilst it’s a fun exercise in imagination, there is absolutely no use in looking at any form of precipitation chart beyond (if I’m being really generous) 90 hours other than for a brief fanciful glance if you really want to torture yourself.

Regardless of whether we do end up with the second half of the winter that from everything we can see from the world of GSDM (and beyond!) really should happen, can I just take a moment to thank you on behalf of the entire thread for your enlightening, simple to understand messaging about what is an incredibly complicated area of atmospheric physics and dynamics. (You’re not alone in this regard either) There’s already quite a few posts creeping into the “background signals have led us up the garden path” territory, without any appreciation for the fact we are all just human beings, sitting on a completely free to use weather forum, giving up time to try and make sense of the increasingly chaotic nature of our meteorological world. ——- We will have to wait and see whether the chaos of the most recent NWP output comes to pass. Unfortunately rarely do the nice clean cut synoptics out beyond day 5/6 come to fruition. But we’re still well out of the reliable timeframe for trying to resolve shenanigans over regions of the earth where data input coverage is quite sparse. So just as I would not have been taking model runs of the last few days too seriously for next week just yet, I still wouldn’t be until at least Friday. I think someone mentioned the GFS in Jan 2013 the other day which was dragged kicking and screaming 48 hours out to the cold camp. Deterministic runs are just throwing out any number of ensemble outcomes - of which there are truly many for our locale right now - at random, and ensemble suites as a whole continue to swing back and forth at surprising rates. Until all of that settles down we just cannot be sure of the details at all.

That shortwave is a classic GFS struggling to deal with the balance of jet energy heading north/south (what is referred to often as a split flow). It's why at anything beyond day 5 we really should reserve judgement until we've seen the ensemble suite accompanying it. I could of course caveat that - we would expect the higher resolution runs to be amongst the first to correctly handle this delicate balance of split energy, but it is unlikely to have nailed that at day 6 just yet (and the GFS is about as likely as the CMA to be the first to handle it correctly). Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4996486

Here's the key timeframe for the GFS's latest little wobble: GFS: UKMO: UKMO sends everything into the southern arm (which tends to be what happens when we see a split flow within the context of tropospheric wavebreaking), GFS sends what I suspect is too much north. To be fair, the GEM does also send a little more Northwards and is probably a halfway house between the two: And a stopped clock is right twice a day, so this could be the GFS's day of triumph. More often than not though through the years we've seen the GFS struggle more than it's NWP brethren in these complex situations

That shortwave is a classic GFS struggling to deal with the balance of jet energy heading north/south (what is referred to often as a split flow). It's why at anything beyond day 5 we really should reserve judgement until we've seen the ensemble suite accompanying it. I could of course caveat that - we would expect the higher resolution runs to be amongst the first to correctly handle this delicate balance of split energy, but it is unlikely to have nailed that at day 6 just yet (and the GFS is about as likely as the CMA to be the first to handle it correctly).

I can’t remember the last time I saw so much of the tropospheric vortex shifted over to the eastern half of the northern hemisphere. Even in 2010 I think there was more residual low heights left to our west than we are currently seeing forecast via ensemble means. Truly astonishing Synoptics on offer. Prepare for the shortwave dramas as we feel this into higher resolution timeframes and we see the effect of all that cold air interacting with some warmer than average SST’s The current envelope given the range offers a lot of high risk, high reward in terms of snowfall potential. But if nothing else let’s enjoy seeing a near flawless countdown from seasonal modelling > GSDM > NWP of some significant blocking across the northern hemisphere. At least another 5 days of hiding behind the sofa waiting to get into accurate range of international @Scott Ingham day.

Nailed it. There are a surprising amount of egos for what is an enthusiasts/hobby forum by and large, and I mean that in both directions - there are also posters who will defend to the hilt that they were right to forecast something which didn't happen, when in reality sometimes we all just need to hold our hands up and say we got it wrong, let's all move on with our lives. But there is nothing more infuriating than seeing a lot of "I told you so" type posts when in reality they have forecast absolutely nothing. There's nothing wrong with coming onto here and not forecasting anything, in fact the overwhelming majority of readers and contributors to this topic do just that (I find myself doing more of that these days too owing to family commitments largely, though there is an increasing element of being put off from posting by some of the I Told You So-ers too). But when people do take the time to offer their thoughts, and particularly those posts which offer incredibly valuable insights, regardless of the outcome of the overall forecast we should not discourage such posters from contributing for the sake of some fast-tracked endorphin hit of saying "I told you so" to somebody you've never met on the internet, that in reality you would never say to them if you met them in person. This is not a new phenomenon either. Back to the earliest days of the BBC Snowwatch forums this behaviour was rife too. Maybe there is something intrinsically egotistic about a bunch of amateur weather forecasters (interspersed with a few pros too) all being brought together into the same space, but it does seem to be just a baked-in online behaviour nowadays. What I hope for more than anything is that these negatives never discourage people from posting overall and that the majority of members recognise this thread for what it is - one of the most fantastic learning opportunities available anywhere on the internet (really what the internet was intended for in the first place). I learned so much from these forums and this topic over the years in particular that it enabled me to become a paid weather forecast for a period in my life, something which I never thought would actually happen despite it being a (very cool and not at all nerdy, I'm sure you'll agree) childhood dream job. And what I would say from my slightly distant viewing of the forum this year so far is the learning opportunities, if you can overlook some of the bickering and peacocking, just continue to get better and better. Some of the recent posts from @Catacol, @Uncertainty, @Met4Cast, @Tamara, @Mike Poole, @bluearmy and many, many, countless others who I will have forgotten in that list are such a valuable, free resource of learning which I hope everyone really appreciates the true value of. You're getting daily free lessons in some of the most complex atmospheric/oceanic physics you could ever wish to learn about, all broken down into significantly easier to understand language which hopefully allows ever more people access to knowledge which otherwise is tied up in needlessly overcomplicated academic writing formats. So on behalf of everyone here to make sure all those countless, wonderful contributors feel a bit of love rather than pessimism and sniping, a huge thank you to all of the posters who have already or will continue to in the future keep helping hobbyists, enthusiasts and potential future meteorologists learning more and more about the weather on this tiny island (and way beyond) in the seasons and the years to come.

Very much worth bearing in mind, particularly those with tendency to follow the trials and tribulations of each individual operational run, that whilst we have an evolving Arctic High in play (such as can already be seen relatively clearly in ensemble means by day 9) then the modelling across the northern hemisphere is likely to be chaotic for many days to come. We will see swings back and forth. The best advice I can possibly give if you want to follow NWP religiously is stick to the ensemble means for the foreseeable: Exciting watching ahead.

Well despite the memories of December 2012 still being scarred into my hippocampus, I always prefer the chase for scandi-based heights than Greenland ones. Why? Well you’re probably all sick of me banging on about NWP’s tendency to overestimate height rises to our NW in the medium range. What we’ve found, however, many times down the years is that modelling at longer ranges tends to underestimate the potential strength of blocking to our north-east, mostly it would seem due to the distribution of split flow energy coming out of the jet stream across the Atlantic always tending to err more towards putting greater-than-reality strength into the northern arm. Then as modelling counts down closer to T+0 we tend to see lows taking a more southerly track with the chain reaction of subsequent events conspiring to leave us with an even stronger high than modelled at longer distances. Now as ever with one of my posts (where’s the fun in getting off the fence) there is a caveat - one of the big spoiling factors which seems to have increased in frequency in recent years is the reluctance of the Azores high to just bloody well sling it’s hook and leave us some space for lovely Genoa-ish low heights to help draw in the coldest air from our east (presumably due to climate change-linked expansion of the Hadley cell). This has, many times, left the UK frustratingly on the periphery of some really severe winter outbreaks across the North Sea. That, at this stage, would be my major watch factor. I am far more enthused at the prospect of this potential chase than I have been with the recent spell - impressive and nice to see as it is/has been so early in the season, it never inspired much confidence in anything too impressive snowfall wise. Lets hope this next one is worth waiting for Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4965037

I think this is very fair. We can probably throw 2013 into the mix for this one - far from a true scandi high, more one of the rare sightings of the GIN corridor wedges. But again in that instance, modelling was not interested in any sort of height rises to the NE until it drew closer to T+0. We’ve obviously come a long way since then modelling dynamics wise, but it’s going to be interesting to see it play out.

Well despite the memories of December 2012 still being scarred into my hippocampus, I always prefer the chase for scandi-based heights than Greenland ones. Why? Well you’re probably all sick of me banging on about NWP’s tendency to overestimate height rises to our NW in the medium range. What we’ve found, however, many times down the years is that modelling at longer ranges tends to underestimate the potential strength of blocking to our north-east, mostly it would seem due to the distribution of split flow energy coming out of the jet stream across the Atlantic always tending to err more towards putting greater-than-reality strength into the northern arm. Then as modelling counts down closer to T+0 we tend to see lows taking a more southerly track with the chain reaction of subsequent events conspiring to leave us with an even stronger high than modelled at longer distances. Now as ever with one of my posts (where’s the fun in getting off the fence) there is a caveat - one of the big spoiling factors which seems to have increased in frequency in recent years is the reluctance of the Azores high to just bloody well sling it’s hook and leave us some space for lovely Genoa-ish low heights to help draw in the coldest air from our east (presumably due to climate change-linked expansion of the Hadley cell). This has, many times, left the UK frustratingly on the periphery of some really severe winter outbreaks across the North Sea. That, at this stage, would be my major watch factor. I am far more enthused at the prospect of this potential chase than I have been with the recent spell - impressive and nice to see as it is/has been so early in the season, it never inspired much confidence in anything too impressive snowfall wise. Lets hope this next one is worth waiting for

Absolutely this. I can’t believe that so many years have passed by with so many phantom height rise debacles and yet despite numerous upgrades to all model suites in the intervening years we still don’t seem to have solved this modelling tendency. I always tend to be sceptical of height rises to the NW beyond day 5 because of this reason. One of these days soon the modelling suites will call one correctly, but it will very much be stopped clock syndrome when they do.

Well I’ve stayed relatively quiet for the last few days, mostly owing to not yet seeing too much in the way of excitement with regards to large scale, lowland snowfall. If I were living in the northern half of the Uk, particularly with some elevation, then I would be feeling much more optimistic. But certainly for the next 5-7 days I suspect there will be a lot of marginality as we see our relatively cool airmass interact with our very positive SST profiles around the UK. My suspicion is that we are just that one week too early, and places further south may well be reliant on some nocturnal cooling to aid dew points and wet bulb temperatures in supporting snowfall. That said, the longer we can lock this pattern in for, the more we should be able to draw that cold pool in from the NE, as per some of the commentary in here this afternoon, let’s just hope for a nice clean transition next week with the broad upper trough. It is also of course worth bearing in mind at this stage that things have been very much tropospherically driven. Even a major deceleration in the stratospheric zonal winds, let alone a full blown reversal, could basically result in a big shake up of the tropospheric order (assuming a downwelling) - think of it like a game of blackjack. We’ve already been dealt a hand of 18 by the troposphere. Do we want to stick, or do we twist with the stratosphere and hope for a 21. Lots of high risk, high reward stakes both shorter and longer term incoming. Original post: https://community.netweather.tv/topic/99428-model-output-discussion-mid-autumn/?do=findComment&comment=4958462

Well I’ve stayed relatively quiet for the last few days, mostly owing to not yet seeing too much in the way of excitement with regards to large scale, lowland snowfall. If I were living in the northern half of the Uk, particularly with some elevation, then I would be feeling much more optimistic. But certainly for the next 5-7 days I suspect there will be a lot of marginality as we see our relatively cool airmass interact with our very positive SST profiles around the UK. My suspicion is that we are just that one week too early, and places further south may well be reliant on some nocturnal cooling to aid dew points and wet bulb temperatures in supporting snowfall. That said, the longer we can lock this pattern in for, the more we should be able to draw that cold pool in from the NE, as per some of the commentary in here this afternoon, let’s just hope for a nice clean transition next week with the broad upper trough. It is also of course worth bearing in mind at this stage that things have been very much tropospherically driven. Even a major deceleration in the stratospheric zonal winds, let alone a full blown reversal, could basically result in a big shake up of the tropospheric order (assuming a downwelling) - think of it like a game of blackjack. We’ve already been dealt a hand of 18 by the troposphere. Do we want to stick, or do we twist with the stratosphere and hope for a 21. Lots of high risk, high reward stakes both shorter and longer term incoming.

What a horrific night. Does anyone really genuinely enjoy this? Only indoor thermometer I’ve got working at the moment is in the nursery and it’s been 24c+ in there most of the night, poor little thing was up at 4.30 for a drink to cool down. That was with a portable air conditioner running all day. I can’t complain too much as we’ve been a bit fortunate really since June, especially in comparison to last year, but I can’t wait to see the back of this muck.

15 or so years ago you would definitely be confident heading into a winter with eQBO and El Niño (provided it doesn’t tick into +2 and over territory) of calling for some colder than average periods. However given recent discussions around the expected tropospheric responses (or lack of) to ENSO I think all bets are off. My suspicion is the longer range models are being led almost wholly by the ENSO signal here, and sadly I’m not sure we can rely on such analogues any more.

This is an absolutely crucial point, and it's something which has been noticeable on a smaller scale now for a number of years from what I have observed, but there's no doubt that this summer is by far the starkest example of successions of micro overriding the expected macro. There are many places to look for the causes of these micro scale feedbacks but we have to start by looking at the oceans : With that level of hemispheric anomalous warmth we have to pretty much throw out the rulebook on everything we have all so diligently tried to get a handle on during the last 15-20 years (few more so than yourself @Tamara) and start to apply further new learning. Unfortunately with the world changing so fast now I suspect this learning and re-learning is going to manifest in ever smaller cycles. Nobody has been able to call the medium to long range over the past few months utilising any source, and for very good reason. The only predictable thing is that tantrums on here will increase at several standard deviations above the expected rate as things become more chaotic. Original post: https://community.netweather.tv/topic/99056-model-output-discussion-mid-summer-onwards/?do=findComment&comment=4896487

This is an absolutely crucial point, and it's something which has been noticeable on a smaller scale now for a number of years from what I have observed, but there's no doubt that this summer is by far the starkest example of successions of micro overriding the expected macro. There are many places to look for the causes of these micro scale feedbacks but we have to start by looking at the oceans : With that level of hemispheric anomalous warmth we have to pretty much throw out the rulebook on everything we have all so diligently tried to get a handle on during the last 15-20 years (few more so than yourself @Tamara) and start to apply further new learning. Unfortunately with the world changing so fast now I suspect this learning and re-learning is going to manifest in ever smaller cycles. Nobody has been able to call the medium to long range over the past few months utilising any source, and for very good reason. The only predictable thing is that tantrums on here will increase at several standard deviations above the expected rate as things become more chaotic.

Equally I don’t understand how anyone enjoys trying to sleep in unairconditoned, overinsulated houses in hot, humid conditions. It’s even more complicated in my current situation with a very young child and trying to keep her cool with the fear of god of SIDS which is a significantly higher risk when you can’t keep their bedroom under the recommended 20c (struggling to keep it below 24c at the moment with blinds and curtains shut all day). We all have weather preferences and that’s absolutely fine, but just as there are consequences for the vulnerable in winter with long cold spells there are equally, if not worse risks in a country whose housing stock is designed to keep heat in, further risks associated with it getting even warm, never mind hot for long periods of time in the UK.

If only Liam! Unfortunately that is total snowfall - assuming that everything which has fallen out of the sky settles. Here's the equivalent snow depth chart for the same timeframe from the GFS - looks much more in line with expectation:

Was just about to post about this (not specific to ICON, but highlights the point). Lowland snowfall tomorrow during daylight hours is going to be quite tricky to achieve, certainly if you're expecting anything of the accumulating nature. This is not one of the situations we've seen at times in the past where we have moisture running into properly embedded cold, this is marginal from the word go. We're reliant on both evaporative cooling and pulling in colder air from the NE - from a zone on the continent which is not as cold as it would ideally be for us. Overnight tonight and after dark tomorrow I suspect we will be fine, but as Tim notes above (and as @Catacol alluded to a couple of days ago), we should not take for granted that anything falling out of the sky tomorrow will fall as snow. Intensity is going to be key and I suspect a very narrow strip is going to strike the jackpot.

Awaiting the 15z UKV, but should be noted that the 12z UKMO-GM is significantly further South with the precipitation for Wednesday (to the point it misses the UK overnight) and is not much interested in much in the way of snow tomorrow morning. We're approaching the point where radar watching becomes more useful than model watching. 12z UKV vs 12z UKMO-GM for comparison