I wonder what the collective noun is for a number of NWP models? You know the kind of thing – a murder of crows, a murmuration of starlings, an exaltation of larks. Perhaps its simply a pile of crap? That may sound a bit harsh, but that’s the thought that ran through my mind when I compare short-range model output in this current spell of severe weather across the country.
All I really want to know is how long is it going to snow, and although they all provide you with some kind of solution, they are all quite different and not that convincing. In the early 21st century you might have least expected some commonality between them at the T+18 or T+24 range, but no that doesn’t seem to be the case, well at least not with the forecast for midnight tonight. Perhaps I am just too naïve to have thought they would have been, probably because I watch too much Star Trek. Perhaps it’s the ongoing SSW event that’s sending the models a little crazy at the moment, I would be fascinated to see just how the UKMO model is coping with the current situation, hopefully it’s better than this lot:-
The latest T+06 frame from the GFS doesn’t fill me with confidence in how the model is handling the re-intensification of low Emma over the next 36 hours or so (fig 1). The showers that were pulled across from the Thames estuary yesterday evening in the strong to gale force easterly gradient, have now morphed into a continuous band of slight occasionally moderate snow that now straddles the whole of southern England (fig 2). This overnight snow in the south wasn’t foreseen in last nights forecasts as far as I can remember. Who knows it might be because the whole thing is becoming less convective and more cyclonic as the pressure falls.
I’m not complaining mind, as it’s not very often that you get powdery snow with temperatures of -5°C in mid-Devon! There’s no sign of any rain over western France yet, although pressure contains to fall steadily.
Rather surprisingly Dublin is as snowy as any other station in this mornings 06 UTC SYNOPs, reporting a level snow depth of 16 cm from showers coming evening off the Irish Sea.
On what is probably going to be the coldest day of this present cold wave across our part of Europe, there has been a widespread severe and penetrating frost overnight. Thanks to a snow surface (I’m guessing there is one there even if they didn’t report one), the coldest low-level station was South Farnborough where the temperature fell to -11.7°C.
Even by 09 UTC this morning, the only station in the British Isles to have an air temperature above freezing was St Mary’s on the Scilly Isles with 0.2°C (fig 2), after reporting a rare frost with a minimum [18-06] of -0.5°C.
The snow showers have just kept coming, and it looks particularly bad today over SE Scotland and NE England, with more snow showers in a strong easterly wind that must be causing some pretty deep drifts. I wonder if the Met Office will issue a red alert for snow and blizzards for the borders or the central belt of Scotland before it’s done?
The spell of snow forecast for the southwest later on Thursday could produce some large snowfall totals before milder air eventually clears it all away. I’ve got a feeling that we might get fed up to the back teeth of March before it’s done, as it looks likely to remain cold and cyclonic till at least mid-month in the latest GFS model run.
Here’s how the Met Office see March panning out (fig 3):
I find the line “towards the middle of March it may turn more unsettled and less cold” rather strange. Do they mean unsettled compared to how the weather is now, or over the next few days? It’s as if the medium range forecaster hasn’t seen the latest NWP, because the scenario that he describes may happen mid-month, is already forecast to happen at the beginning of the month (fig 4).
Thursday is shaping up to be a real humdinger down across the southwest. The Met Office forecast charts – which are already out of date – are suggesting that the vigorous low that was forecast to be close to southern Ireland will stay much further south (fig 1). Although this will still allow much milder air to push north across the country above 850 hPa, it will find it more difficult to push down to lower levels flow as colder air is pulled in from the east, and the warm sector will slow as it comes up against the colder air and starts to occlude. This is a classic recipe for 12 or 18 hours of continuous moderate or heavy precipitation across southern areas. A period of heavy snow is possible, certainly across any higher ground and away from the coastal strip, and that’s probably why the yellow warning for Thursday across the south has just been upped to amber by the Met Office (fig 2). Let battle commence!
What happens after Friday?
It’s always difficult, even impossible and try to second guess what the UKMO model will do after T+84, because you simply can’t see it! Even what you might think is UKMO data on the BBC forecast these days may well be GFS data. Both the GFS and the ECMWF models make low Emma the dominating influence during the coming weekend and into next week as the easterly flow collapses and things become cyclonic.
There’s a cold and very wintry week ahead across the whole country according to the latest suite of forecast charts from the Met Office (fig 1). But they never extend beyond four days, which is a great pity, because that’s when the real fun and games start.
It does look like it will all end in tears though for the snow lovers amongst us though, as the anticyclonic easterly that we have at the moment is cast unceremoniously aside in the latest GFS run (fig 2), by a vigorous low that tracks northward from Biscay later on Thursday and into Friday bringing a swift return to the milder cyclonic weather that we’re used to, at least across southern areas.
Even the ECMWF is now following the GFS lead (fig 3). Of course the models beyond T+72 have been so volatile in recent weeks this may not happen exactly this way. Whatever process is behind the steering of this low might take it east a long the English Channel rather than north – we live in hope.
It’s interesting to see how this impending cold snap has got many people excited about it, even those that don’t usually give a hoot about the weather most of the time, it’s almost like the announcement of a very early Christmas. I saw a good example of this in a tweet from Weather Outlook (fig 1) saying how the ‘thickness’ would fall below 500 dam in NE Scotland – really?
Just to check that I hadn’t just entered the Twilight Zone I looked at one of the few sites that does include a 1000-500 hPa partial thickness forecast chart these days from NOAA (fig 2).
As you can see 1000-500 hPa thicknesses for next Wednesday are expected to be below 528 dam (the old blue or snow line) across most of the country except the west of Ireland and NW Scotland, and the 510 dam (the old brown line) has just about engulfed Belgium. To put this cold spell into some kind of perspective here is the thickness chart from the 13th January 1987, in what I reckon was the coldest couple of days in the British Isles of the whole 2oth century (fig 3).
I have seen in the last few days people displaying forecast sequences of 850 hPa temperature charts on social media – which I also like to do – and people on Facebook and Twitter thinking that the -15°C isotherm at 5000 feet is the forecast surface temperature!
So in the scheme of things a good cold snap, even very cold for a day or so, but not record breakingly cold. One thing that would make this cold spell memorable though is the length of time it persists into March – which at the moment is still up in the air!
There’s good inter-model agreement now at T+72 for the start of the anticyclonic easterly brought about in part by the recent SSW event over the North Pole (fig 1).
Early next week looks particularly cold with a cold vortex of -19°C at 850 hPa temperatures across central Germany (fig 2). Those low temperatures at 850 hPa equate to 12 UTC surface temperatures below freezing for much of the UK (fig 3).
If this meteogram is correct it looks like as well as being dry, windy and very cold in the southwest, it should also be sunny by day and clear by night (fig 4), and there’s an interesting blip in the hyetograph by day 10 to give us something to look forward to as well.
This item just wouldn’t have been the same without the help of the excellent NWP products from wxcharts, lets hope they don’t start charging us for the privilege anytime soon! This is exactly the kind of free service that we should expect from our own Met Office – it’s going to get very cold in the next few weeks – but hell would have to freeze over before that ever happened.
The latest run of the GFS has come back into line with the ECMWF model in establishing a cold anticyclonic easterly across the country by T+144. After that the GFS enters the twilight zone by introducing a number of cyclonic outbreaks that get embedded in the cold easterly flow, these suggest a high chance of substantial spells of snow especially in eastern districts by the end of the month (fig 1).
Even the Met Office are now warning of the increased chances of this happening thanks to the recent Sudden Stratospheric Warming event above the North Pole. Professor Adam Scaife, of the Met Office Hadley Centre, said:
“Signs of this event appeared in forecasts from late January and in the last few days we have seen a dramatic rise in air temperature, known as a Sudden Stratospheric Warming, at around 30 km above the North Pole. This warming results from a breakdown of the usual high-altitude westerly winds and it often leads to a switch in our weather: with cold easterly conditions more likely to dominate subsequent UK weather.”
Frank Saunders the Met Office Chief Operational Meteorologist said
“A Sudden Stratospheric Warming implies around a 70 per cent chance of cold conditions across the UK. There tends to be a lag of about 10 days before we see the downstream effects on the UK’s weather, as it takes time for the influence in the upper atmosphere to feed down to those levels where our weather happens. The outcome for the UK’s weather is still uncertain, but forecasts from computer models at the Met Office and at other centres are beginning to coalesce around a greater likelihood of cold conditions in the days and weeks to come.”
Just when we thought that we finally might see some winter down here in the south it now looks like two of the three main NWP models can’t agree with how things will work out in just 6 days time. The difference at T+144 between the GFS and the ECMWF models is massive, with the GFS going for a cyclonic SW’ly (fig 1), and the ECMWF for an anticyclonic E’ly (fig 2). All I can think is that it must be how each model handles the current SSW that is behind these two widely different solutions.
There is no doubt that a change of type will occur in the next week or two because of the SSW that started late last week. The next problem is where the actual block will be positioned and orientated. The two main available NWP models at T+240 have different views on that matter at the present time. The ECMWF has the block centred over the southern North Sea at the 500 hPa level and aligned northeast-southwest (fig 1), whilst the GFS has it centred over NE Greenland, and ridging more or less north-south across Iceland towards western Ireland (fig 2).
The exact position of where any block sits at the 500 hPa level, will make a big difference at the surface, because it dictates the surface flow and the source of the coldest air. As you can see the ECMWF at T+240 has higher than average 850 hPa temperatures across the UK in a strong SE’ly flow, and the coldest air over SE Europe and the Balkans (fig 3).
Meanwhile the GFS model has the coldest air at 850 hPa over Scandinavia with the UK in a much colder regime and the flow more easterly and not as strong (fig 4).
Here’s what the experts are saying down at the Met Office about the medium term (fig 5).