I am reliably informed that the spring vernal equinox will occur at precisely 1615 UTC today this 20th day of March 2018, but the weather is in a fickle mood at the moment, and spring, well at least the start of it, looks like it will be a cold affair in our part of the world. The Met Office in their extended outlook till the middle of April (fig 1) is being its usual unequivocal self about the possibility.
In line with that outlook, the GFS model for April 1st (fig 2) is forecasting a northerly outbreak which is not at all unusual for spring across the British Isles.
Cold springs are somewhat of a rare commodity these days, and the last one to produce negative anomalies in Central England was back in 2013 (fig 3), and in the last 30 year there have only been three cold springs (2013, 1996 and 1991).
I did say last Sunday in the article return of the easterlies that it was still in the land of science fiction, well the models look to have been spot on even at T+168. The Met Office have a discrete centre of 1002 hPa on the low that seems to form on the northern edge of a warm trough that’s moving westward across France for 12 UTC on Sunday (fig 1). None of the other models, apart from the French ARPEGE seem to have pressure as low as that across the Channel on Sunday (fig 2), although it’s difficult to synchronise the validity time. It’s still 72 hours away, and we are now close to the vernal equinox, but this situation has the potential to cause a lot of disruption, especially if snow falls in the overnight period.
Today’s 06 UTC (Friday) from the GFS has a similar feel to it at T+42 (fig 3).
Still out there in the realms of science fiction land I know, but the last few runs of the GFS model have had pressure building strongly across Scandinavia later this week that pushes low pressure further south into central France, leaving the UK in another easterly air stream by next weekend and just in time for the vernal equinox and the real start of spring (fig 1).
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).