snowking

Latest Euro 4 very much in line (and probably an influencer of) the met office warning areas 2-5cms widely, 10-20cms for Eastern parts of Suffolk and Essex along with Northern Kent - and that's only through until lunchtime on Sunday....

Yeah very difficult to call for these parts at the moment. We're right where I wouldn't want us to be which is on the edge of the yellow warning area - I suspect the immediate northern-western edge of the yellow warning area will do least well overall in this region as they miss out on the bulk of the frontal precipitation and then get prevented from benefitting from any showery activity for at least 24 hours thereafter. This thing is still moving around a fair bit so scope for some movement of probably 30-50 miles in any one direction, the trend has been further South and East over the last 24 hours or so though it must be said. Very glad that some of the folks further East in the region who have had a bit of a naff time of it so far this winter look set to cash in big time here

It shows how spoilt we have been by recent output that I’m pretty underwhelmed by the 12z ECM. Looks good for the eastern half of the region though. On to the next run!

Always good to get a view of the behind the paywall output, cheers Dan. These charts will probably still be an overestimate, but given the likely nature of the snowfall (the powder kind), the 10:1 snowfall to liquid ratios used to calculate these will probably be much closer to the truth than they usually would be for the UK (usually this ratio is chosen as it is the sort of ratios they get in the US where most of their snowfall tends to be more on the powdery side, but this is often less true for the UK). Still a nervous wait through until Saturday to get a better grip on where this ends up, but I don't think too many in here would be disappointed with that.

Trying to figure that one out myself Nick - given the flow on the +144 chart we must be missing something between +120 and +144 to end up with those 850mb temps. I'm not complaining about it, but was a bit of a head scratcher. I think Nick S is right in as much as on this particular run the +168 chart would show trough disruption - but it's a far less comfortable scenario for many south of the Humber to be faced with (vs what was previously modelled), particularly given we don't get the very coldest air fully across the UK and certainly into much of France before we see the attempted Atlantic intrusion. Anyway all too much detail for +144 given the current levels of entropy. But still we wait for some consistency

Exactly what I was thinking. It's a significantly better run than recent GFS runs, but it's far from what we were hoping to count down to from just a few days ago. We'll need to see what happens as the various runs (hopefully) settle down over the next couple of days, but we seem to be moving away, at the moment at least, from what was shown - a few days "proper" (or convective) easterly with a continental influence - towards more a brief incursion from the east, followed by watching how much any residual Atlantic energy can undercut the cold we manage to get in situ. Whilst so many models are showing so many different things everything is still on the table, but the current direction of travel, it looks to me at least, is away from a more convective easterly and back towards something more akin to a battleground scenario. I hope to see that direction reversing somewhat starting with the 12z ECM.

UKMO snow depth at +144 (probably take amounts with a pinch of salt as I think these run with a 1:10 ratio) If you want to view them yourself here's the link: Model charts for United Kingdom (Snow depth) | UKMO (6 days) METEOLOGIX.COM UKMO (6 days) - Current forecast valid for 02/07/2021, 12:00pm of parameter "Snow depth", model chart for map "United Kingdom" It's 24 hours later we would ideally want to see. Terrific 12z output so far, though as has already been caveatted, everything has to go perfectly to achieve an output like the 3 higher res GFS outputs this afternoon. Here's to hoping.

Indeed. One has to hope this is a monumental failure from the ECM det. But there comes a time when Op run after Op run keeps the same theme at such short range (relatively) that you have to wonder whether it’s resolving something it’s lower resolution ensemble suite simply isn’t able to resolve with any real conviction. As for the UKMO, brilliant output, but I think the memories of some are too short here given how much we have seen it flap about this winter season. At day 4/5 you really want to see the Op runs from major suites aligned, otherwise we usually end up with a middle ground solution, which would be rather disappointing in this instance.

Many reasons to be suspicious of this GFS 12z run. If we compare the Z500 anomalies to that of it's own 6z suite and the 0z EPS: Note entirely outside of the envelope, but different enough with the angle of the troughing to make it suspcious. Of course if we want an even easier way of seeing why it should be treated with caution, we can just compare it at the same time synoptically to its previous run: A vast enough difference that I think it's wise for us to question the validity anything beyond Day 6 at the moment.

It may end up being an outlier within its own suite, but if you're looking for support for this evolution, look no further than last night's EC46: Scandi block > Atlantic Ridging > -NAO (i.e. Greenland block)

Scandi Block > Atlantic Ridge > -NAO Classic retrogressing Scandinavian high signal (even though I suspect the retrogression will be slightly slower than that)

Yeah I think it is worth saying on this that we should remember the lessons of very recent history. The ECM op probably ended up being closest to the actual outcome, but even this was not 100% on the money (the greatest snowfall totals were a little further north than even it modelled). It essentially ended up being a radar watching event. I fully expect the same to be true of Saturday's event, but it's worth noting that the event this Saturday is really rather different dynamically to that of the weekend just passed. Last weekend, we saw a developing shortwave/LP system develop as a disturbance as it ran into the UK. This weekend, we see an already developed LP system running into advancing cold air from the north. These sorts of systems are the ones that tend to correct Southward the closer we get to the event as models tend to underestimate the stubbornness of colder airmasses historically. It's also worth noting the conditions will be considerably more marginal than they were last weekend and it's likely to be rain turning to snow as the colder air filters in, so we will likely be more reliant on the intensity of the precipitation to help us somewhat. On the flip side I guess, the slightly less cold nature of the air does give more of a chance of the precipitation advancing further North than we may have seen historically too. So far from certain and we likely won't know what's happening until the Saturday itself.

I haven't had much time to look into things too extensively lately with a heavy workload. So we're in the period of the last third of Jan that I and many others had hoped would bring some significantly wintry weather to the UK's shores. And whilst many of us have been lucky enough to see snow, and indeed through the rest of this week that will continue to be the case, there is no dressing up that the 'big boom' winter synoptics we would have hoped for during this period, courtesy of our SSW, have not come fully to fruition. In truth I think we have been desperately unlucky, given the synoptic setups we have seen, to have had such a warm early season across Europe so as to prevent something which in previous years, with similar synoptics, would have delivered far more. A lesson learned here that even though we saw some temporary splitting of the stratospheric vortex at various junctures following our huge Wave 1 displacement event, Wave 2 led vortex disruption events and their (usually) consequent far more significant splitting of the stratospheric polar vortex offers probably a greater chance of something more significantly wintry in our part of the northern hemisphere. All of this being said, the stratospheric warming episodes which have already occurred, and the one due to occur once again over the coming days, have already done lasting damage to the stratospheric vortex, and left our tropospheric vortex in relative tatters compared to other winters in the past 25 years - here's an example of where we are this year, vs where we have been in previous years (2019/20 used as the example here) So, the stratosphere has done its part (as much as it can given the dynamics this year), and left us with a relative void of westerlies at northern latitudes throughout the stratosphere and troposphere, as demonstrated nicely here on the ECM op day 9 zonal wind profile Over to the troposphere now to play its part. There have been two things we have been sorely lacking in from what I can see from a tropospheric perspective (and the cause of this is still to be hotly debated - at the moment, La Nina seems to be the most mooted contender, particularly when taking tropical influences, or lack of, such as the MJO into account - we'll leave this for another time) - positive global angular momentum through January, and assistance from the tropics. Well, we may be about to get both. Relative angular momentum tendency seems to be on the way up, the screenshot below taken from Ant Masiello over on Twitter as I've lost my links through to such analysis (if anyone is able to help with the links to where these now live that would be greatly appreciated!) The net result of which we would expect to be a much more ridgy/troughy longwave pattern - think plenty of opportunity for blocking highs to occur. Then the second, very well advertised ingredient which may be able to ride to our rescue and allow the troposphere to take advantage of the relative lack of westerly momentum imprinted from the stratosphere above, is the MJO movement through to phases 6 and 7. I wont re-post these as they have been very widely covered in here already, but let's keep in mind that phase 6 would tend to suggest high pressure at slightly lower latitudes than phase 7 in our vicinity at least. So where does that leave the thinking for the 2 weeks ahead? My punt at this stage would actually be something very akin to the recent GFS para output, such as this at day 10: Main features for me are: 1. Would expect more of a high pressure cell close to the N of the UK - Norway through to Iceland, somewhere close to that. What that probably means initially at least is something much colder and drier for many (probably welcome relief in flooded communities). 2. As we transition from MJO phase 6 through to 7, expect any high pressure to gain latitude with time. This should allow for something a little more interesting as time goes on in terms of snow potential. I would also be suspicious of any model output promoting anything too west based in terms of the NAO at this stage too - it's more of a hunch than anything, but given the relative lack of momentum in either direction currently, along with the likely uptick in angular momentum, I can see that with movement from MJO phase 6 and 7 the opportunity for high pressure to move further North with time, but I'm not sure where the forcing would come from for drastic retrogression of any blocking pattern within the next 14 days. Final note from me - this sort of ensemble mean suggests huge potential to advect some very cold air from East to West through Europe - there's a reason @nick sussex loves a Genoa low (although this may leave us just a little short of that). Angle/alignment of such features all still very much to be worked out, and plenty that can still go wrong in the shorter term to prevent us from even arriving at the sort of destination currently modelled through days 8-10 (and as we know from this winter already, anything that can go wrong for UK cold generally will). But with both Troposphere and Stratosphere now doing everything they can to move us towards something seasonal, this feels like our best chance yet.

Yeah there’s definitely something out of sync, I think it might need some recalibration of the geolocation. We were under “precipitation” for an hour here before it started snowing. Now it’s supposed to be bone dry according to the radar yet there’s still moderate to light snow.

This was from @essexweather over on Twitter - latest UKV, which seems to run the pivot to end up along the northern boundary of...you guessed it, the M4.

Just had a short Graupel shower here, which is the first significant wintryness I have seen this winter. Frustratingly I suspect the precipitation coming in from the NW is just about missing us here, and I suspect the precipitation tomorrow will just miss us to the south

Models, as they tend to do, correcting Sunday’s snow southwards now. Unless there is a drastic change in direction, I would be very surprised if East Anglia saw much at all, with areas South of the river looking far more comfortable in terms of snow prospects

For those wondering about the 12z UKMO output for Sunday: Difficult to make out given the big time steps, but it's generally still sliding SEwards

I swear Bedford so far has been the worst place I've lived for snow - it always manages to circle around here Here's to hoping Sunday can break the trend - unfortunately not liking the 6z GFS in this regard

Well not quite the deeper cold we had hoped for at this juncture, but I’m not quite sure why there is the despondency there is in here today. As far as I can see the second half of this week brings further opportunity from the N and W initially, then further chances just about anywhere of seeing some snow into next weekend - as always in slider-type scenarios there are bound to be winners and losers, with those further N in the UK probably feeling far more confident than those further S. However in the day 3-6 range I have often found over the years that models tend to underestimate the resilience of cold air and the level of heights across the northern hemisphere as a whole, so as others have mentioned, there is bound to be some further movement of this pattern yet. Anyone suggesting that the models have had a decent handle on this situation in the last 10 days have clearly been looking at wildly different ensemble suites to me, and we’re by no means done yet with the swings following the SSW and the subsequent (and still upcoming) further warmings

Latest Euro4 still pretty keen on snowfall for much of East Anglia and some parts of Kent/Sussex too. Just to help you match up the scales there, the majority of East Anglia in line for 2-5cms. For a large swathe of Norfolk, Suffolk, Essex and arcing back around into Hertfordshire the scale there shows 5-10cms, and for what looks like a lucky zone across the higher ground of Essex/Herts (and likely I would think back across to the Chilterns too), 10-20cms currently shown, and this has been pretty consistent over the last couple of runs. Worth noting the Euro4 is probably the most keen on snowfall currently - other modelling not quite a bullish as this (I suspect the UKV is slightly toned down based on the current warning in place). It will all come down to just how quickly (or not) the fronts occlude tomorrow - the further West they occlude, the better snowfall chances are

Indeed, and what I fear may go wrong towards day 15-20 is that new geopotential wave from the Eurasian side - you would hope that given how weak the vortex now is that this would be the final knockout blow to it (and it may yet prove to be so), however if recent GFS runs have this modelled correctly (ahem...), this is not the case, and instead as Nick referenced earlier the vortex will instead be sent packing to Alaska instead. Assuming that this imprints tropospherically (which seems to me at least to be the direction of travel), that probably sets us up for a potential period of more Arctic mobility sometime in early February whilst we see the broad trough transfer from East to West There's a lot of assumptions made there, but that would be unfortunate timing should that prove to be the case, but may see us looking NE rather than NW for blocking as February progresses. A lot of water (or icebergs...) to flow under the bridge before we get to there, but one to watch.

I haven't seen the video so I'm just surmising here, but I wonder if he meant that whilst the polar vortex was significantly weakened, it wasn't taken out altogether. If he actually said that it didn't result in a reversal then that is factually wrong (and still is even today), but I suspect he was probably referring to the former.

I see the swings in mood continue on in here. Probably best still yet not to take anything too literally I would have thought given how wildly even the ensemble suites have been swinging, though as noted yesterday I would hope that as of tomorrow, with the stratospheric vortex split into the initialisation data through the stratosphere we might get a slightly better handle on any trough disruption in the troposphere. Another period of entropy to put up with though through until the 18th when the split vortices come back together again. I would still advise taking any runs which dramatically remove higher heights over the arctic region too quickly with a pinch of salt - I'm slightly less confident in that assertion with recent runs I must say, but I'm still leaning more in that direction. Let's see where we are at the end of tomorrow and try not to lose too much sleep in the meantime.

Irritatingly light precipitation now but it is now sleet/snow