snowking

Very useful free output now available from the ECMWF freebies for snow cover forecast - usual caveats apply about the below charts, being a single operational run etc. https://apps.ecmwf.int/webapps/opencharts/products/medium-snow-sic?base_time=202010070000&projection=opencharts_north_pole&valid_time=202010070000 Looks like plenty of snow to come south of 60N further east into Asia, we could do with more of a push westwards for the second half of the month

I thought this may be of interest: So now alongside the EC45, we get to obsess daily over the GFS35....what could possibly go wrong just as we approach the winter season...

To be honest, I would treat the QBO as one of those teleconnections we cannot rely upon for longer range weather forecasting for this year. Given the bizarre nature of it so far in 2020 we don't really have any analogous years to compare it to, with the overall makeup of the tropical stratosphere seemingly different even from our last failed eQBO. So whilst it will have some sort of impact, it's pretty near impossible to predict what this impact might be for the seasons ahead.

Normally only ever when it is in disagreement with the UKMO at the same time in my experience - not always, but that remains the key factor here for me

You know you need to sort your shh...tuff out when you’re behind the GEM at both day 6 and 10. Incidentally, how many times in winter are we praying for a trough to drop SEwards, only for it carry on eastwards to our north.

Yeah when you take a look at the 950mb temperature profile: there would probably be quite a significant melt layer, so away from higher ground I suspect it has gone slightly rogue, although similar shown on Meteociel too with Dew Points around 0-2c

12z EURO4 shifts things south about 30-50 miles - the consequences however, as teased earlier, are that the precipitation is less intense overall and so the result is a sleety mess but further south (Home Counties through to London ), with just some trace temporary accumulations showing up on the highest ground. That said, comparing the 1900 radar imagery to the forecast position of the precipitation band at that time from both the UKV and EURO4, the band in reality looks a touch further north than modelled by these two (by say about 20-30 miles) - so we’re probably honing in on a middle ground solution between high resolution modelling and the more global NWP output (e.g ECM which looks significantly further north than the UKV/EURO4, but in reality is only a touch further north, enough to engage an area of vorticity to the north of the system and trigger some further showers/precipitation)

Whilst the GFS has indeed moved further South on the 6z, generally high resolution modelling has been fairly stable now for the past few runs. Taking the Euro4 as an example, we can see that it has the snow line (certainly in terms of accumulation) pretty much in line with the warnings issued this morning That was actually significantly toned down when compared with the 0z run: You might argue if you look really closely that the Southern-most boundary of snowfall has shifted south about 10-15 miles but that is being generous. That said, I have seen many examples over the years of the reality of the situation being significantly further south than modelled - usually NWP has overestimated the depth of the low and so naturally the system tracks further south. Of course it's also worth bearing in mind that the weaker the LP is, the less intense any associated precipitation is likely to be with it, and I suspect evaporative cooling will be a big factor in where any snow falls (along with elevation of course).

Looking at the ensembles I am increasingly confident that the coldest period of the winter will come between 28th Jan - 2nd Feb. Why? Because I am out of the country

You beat me to it - on the plus side you can indeed see quite a slow down in zonal winds forecast on GLOSEA into early December, fairly in line with the GEFS mean really, which may in itself be enough to help us achieve something interesting in the troposphere as per current modelling. However, it then goes on to show a mean increase in zonal winds through the rest of the season - and given that is beyond the range of any medium range NWP suite that us mere mortals get easy, regular access to stratospherically, it could well be that the GEFS mean is indeed correct in its guidance, but in the longer term a technical SSW is never achieved. Regardless of any of this, whilst every little helps, for as long as we see a decoupled Strat and Trop, we needn’t worry too much about the longer term Strat outlook as far as the first half of December goes for now. One does suspect though that the deeper into winter we go, the more help from above we will require - and I’m not talking divine help here.

The usual (probably quite dull by now) advice from me We should not be too quick to dismiss a single deterministic run, even if it is out of kilter with its own suite (caveat: I have not yet seen the EPS suite), particularly given the higher resolution of the deterministic run in trying to resolve some delicate balances over the atlantic. We simply don’t know at this stage where to judge this run and will need to wait for further runs. My second and definitely tiresome piece of advice is to be very cautious when looking beyond day 5 in the Greenland locale and particularly with regards to any suggestion of increased heights (those lovely greens and yellows on the H500 charts) - we have seen season after season a bias towards increasing heights too much in this area beyond day 5, only for this to correct itself the closer to T+0 we get. At some point, like a stopped clock, the models will sniff out one of these Greenland height rises correctly (and I do fancy that to be this year incidentally), but for now I would urge caution before we drive ourselves towards an early season meltdown. With Brexit coming Nick might struggle to get the Prozac over the border.

I think it’s more just a general discussion to be fair - we won’t know for a few more months whether we are actually seeing a failure to downwell or not. I’m sure if we were monitoring things this closely back in 08/09 we might be wondering whether the same was happening then too: https://www.esrl.noaa.gov/psd/data/correlation/qbo.data The phase change of the QBO is not a linear phenomenon - we’ve seen a few years ago how there can be a miscue of the usual W-E-W-E pattern, but on the scale of month to month we have historically seen some variance in the 30mb series. The truth is, we simply won’t know until early next year - but to finish on an optimistic note, I remember a certain February 2009 cold spell....

From what I understand there are no absolutely clear linkages between SSW’s in the Northern and Southern Hemispheres, other than it does indicate, for now at least, some healthy levels of Ozone transport via the BDO So an active BDO is a positive very early sign, but just as with any index at this range, that can very quickly change and does not necessarily dictate an active BDO season for the Northern Hemisphere winter

Walking through the rain earlier I couldn't help but think we would be crying out for this setup anytime between December-March. Cue the raging SWlies come winter...

Currently sat on a plane at Dublin airport which is having to get de-iced because of the snow which has come down in the last hour - now I can see out of the windows again looks like it’s settled pretty readily

Of course typically just as the heavier stuff starts moving south it dies out - back to lighter stuff again here

Incredibly frustrating isn’t it Nick. It does seem to be very slowly on the way south now and it’s turned more moderate here in the last 20 mins. The slow moving nature is good news if it holds together of course Yep - more moderate now. Hopefully getting heavier in the next hour or so

This has been on my mind for some time now I must say - and the target date for this has been somewhere between 2019-2021. Next year has a lot of positive hallmarks - likely eQBO, solar minimum conditions, ENSO potentially the unknown quantity. In the back of my mind over the last few weeks has been how many times have we seen three consecutive seasons with major SSW’s....but as you say one starts to suspect we are in uncharted climatological waters (pun intended) You can’t help but feel that thus far this season we have been relatively unlucky post SSW (with a few exceptions) when you look at what’s gone down elsewhere around the Northern Hemisphere, but that’s just all part and parcel of the more mesoscale jigsaw puzzle that longer range forecasting (including seasonal modelling) simply can’t pick out as yet. But perhaps a wQBO has hindered what could have been even more of a significant downwelling to a certain extent. With MJO analogues becoming increasingly unreliable we’re going to have to keep on researching, trialling and hoping we can find some further linkages that give us more accurate clues at leadtimes of 2-4 weeks - I don’t get to see the clusters so as Nick has been at a pains to emphasise today when there’s been a lot of bashing going on, we can’t simply dismiss the EC46 output. But given the leaning of the longer range Met Office forecasts in recent weeks it does seem likely that it has indeed called things a little incorrectly for our tiny little island (along with some of the GLOSEA output), and I therefore remain unkeen on using traditional NWP at such long lead times. It’s been (and will continue to be) another season of learning...though I’m not sure what we can learn from this season. Just to embrace the chaos maybe? The only consistent thing with this season and the many before it has been the...ahem...consistent displacement of junior play implements from secure infant transportation....when things don’t go quite according to plan. But for those who accept that we are all trying to predict the future using inexact science with the hope of some white gold at the end of the very long rainbow, next year could be very intriguing indeed

This just about sums up this week in Greenwich: Been sat on the southern edge of that heavier precipitation for the last two hours now, with just some sleet and occasional bursts of wet snow which hasn’t left a slight layer of slush on some cars. And now it’s weakening. So a little like March 18 for this area, so close to something more significant but did not have the winning ticket in the raffle once again. But good to see some areas have done better than expected, and today’s system does go to show that even with the hundreds of millions which we throw at forecast models, some situations are still as unsuccessful as my own modelling career (which similarly even hundreds of millions of pounds could not fix) There’s still hope, we’re only just into February and modelling will remain volatile for a while yet with the downwelling wave, but after the grim weather we’ve had today in London, I think I’m ready for some spring warmth....maybe swimsuit modelling is more my thing...

In parts, but broad scale within 24 hours it called yesterday very well....and the worrying trend which it started now seems to have followed on some of the 12z suites so far We’ll see!

@kold weather any news on the 6z ECM? I have to say the EURO4 is concerning for anyone from London northwards - I’ve found over the last few years that it’s generally a bit all over the place with precipitation intensity up to 48 hours out, once it gets within 24 hours it tends to be pretty good. At 48 hours out, yesterday’s snowfall event looking like bringing a few cms even into central London....then as the runs ticked on, the precipitation intensity slowly died and we saw what we saw last night - a nice little event with elevation, but elsewhere generally just a small covering (if at all) If the ECM is on the money then I will be a lot more comfortable - if we’re slowly heading to a EURO4 solution then for anyone North of the Thames, this could become another disappointment Let’s see how it develops though, lots of complications in the flow with multiple centres of low

I think it's probably more that there's not been much to post about in London away from higher ground, largely sleet and the marginality with the UHE really playing out here I think To be honest, much as @bluearmy posted earlier, I lost interest in this event when the low sank into France, that was the shot at some really decent snowfall. But glad to see that much of the region has seen at least some falling snow, and looking good for those even further East. Thursday looks interesting at the moment , but there's still a whole 48 hours to go with that yet. Hoping it can maintain the signposted intensity

Elevation certainly making the difference it seems in London at the moment. Rain with a bit of Sleet at times so far in Greenwich, it should get more interesting in the next hour.... and then again on Thursday....

Indeed Kold The ECM not really making much of the Tuesday event now it has to be said, much quicker than the others and maybe 1-3cms for most, nothing too distressing. However for Thursday it sees the initial front as sleet/snow for pretty much everyone away from the far South, the band then heads north but stalls and pivots with The Midlands being the big winners along with some parts of N England, there is then a second area of precip which heads into Southern England later in the day, a mixture of rain sleet and snow, but that is all academic for now - we’ve seen even with Tuesdays low a tendency to shift around quite a lot so we are still far from certain where that initial front will actually decide to come to a halt at Euro4 - good looking snow cover but when you check the key, it’s probably generally 1-5cms from the front, so still nothing too significant. But still good to see the likelihood of some widespread snowcover as the week progresses. For me, it’s now all eyes on Thursday

Well if that ECM run is correct, there won’t be a lot to make a fuss over, maybe a few cms here and there Theres another wave ahead of the cold front arrival but given that it head in during daylight hours, it’s mostly rain. And not much steam left on the front when it arrives either Hopefully by tomorrow 12z we should have some clarity