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.