The latest offering from the GFS model predicts a rather cold northwesterly airstream on Christmas Day, a bright looking day with wintry shower especially across northwestern areas. This brief cold snap may well be the last in a series of cold north or northwesterly incursions that you can trace back to the end of October (fig 1).
As so often happens between Christmas and New Year, the weather drastically changes in mood, and this year doesn’t fail to disappoint in this regard, as it turns progressively milder on Boxing Day, and by the start of 2018 its super mild across the British Isles and the bulk of Europe, if this chart for January 1st is to be believed (fig 2).
The GFS solution does contradict the latest extended outlook from the Met Office though, which suggests that in the final days of December “Temperatures will be near to or below average and snow is likely, at times”, they go on to imply that things might turn more settled and anticyclonic as we go into January 2018 (fig 3). As always, it will be interesting to see what transpires in a couple of weeks time.
Snow’s piling up fast over the higher ground of central and southern Wales this morning with Sennybridge now reporting a 19 cm covering of fluffy snow at 07 UTC (fig 1). The latest 3 hour pressure falls seem to indicate that low Xanthos maybe tracking a little further south than the model expected this morning (fig 2).
All is not lost for snow lovers down here in the southwest of England, if the latest GFS T+30 frame for this time tomorrow morning is correct (fig 3).
I have no idea why the Met Office didn’t just name low Xanthos storm Derrick or Dylan or whatever they’d dreamed up, it certainly looks like it will be very memorable to a lot of younger people today, who I should imagine are already getting out their sledges this morning.
Today’s gradient across Liverpool bay has been slightly more backed than it was yesterday, which as allowed a continuous stream of showers to feed through the Cheshire gap throughout today towards the White Peak (fig 1). Estimated accumulations since 06 UTC today in the wettest areas are in the range 16-24 mm. Most of the showers today have been of rain near the coast, but on higher ground inland of snow. The weather certainly looks very wintry at the Cat and Fiddle pub at dusk this afternoon (fig 2).
The ubiquitous jet stream may have something to do with this continuous feed of showers, but I am no expert. This afternoons visible satellite image has been very dramatic, with the sun casting long shadows on the frontal system that’s approaching the west coast of Ireland from the west. There was also a tongue of upper and medium cloud that stretched across Northern Ireland, across Liverpool Bay and East Anglia associated with the band of showers (fig 3).
Compare the 300 hPa winds as the GFS see’s it for 12 UTC today with the curve in the frontal system coming in from the west (fig 4).
I’ve been getting all worked up this week about Monday and storm Ana over northern France. The only reason for that was was that it gave the best chance of some snow here in Devon and the southwest than did the events further north on Sunday. If anything the more significant threat of snow and major disruption is, and probably always was, from low Xanthos on Sunday, which will bring a spell of significant snow to Northern England and the Midlands. The latest GFS still develops a pair of dumbelling lows across the southern UK, with the warm air finding it difficult to push any further north than latitude 52° north (fig 1).
I can’t think that there have been two more interesting days weatherwise than this coming Sunday and Monday, at least not since Christmas and Boxing day 1999. It will be interesting to see if the amber alerts area is expanded later this morning by the Met Office, and if they expect a little more than 15-20 cm of snow in the worst affected areas that they mentioned in yesterdays initial warning (fig 2).
I know I come up with some pretty poor, occasionally ridiculous headlines in my time, but the Press team at the Met Office must have been running short of ideas when they thought of the one for their latest news release: ‘Snow and sun for the weekend‘.
They go onto say about the Weather on Monday:
“Further unsettled and potentially disruptive weather is possible for some southern areas early next week. Storm Ana, named by the Spanish weather service, is expected to move into France on Monday and may bring a spell of wet and windy weather to parts of southern England with the potential for more snow.“
The obvious question is why are the Spanish naming lows that are forecast to track across the north of France?
The 12 UTC run of the GFS has a similar solution to that of the midnight run for Monday at 12 UTC (fig 2). The Met Office news release goes on to say about that:
“The situation will be kept under close review over the weekend“
The snow threat on Sunday now looks likely to be restricted to the north of Wales, the Northwest of England, the north Midlands and Yorkshire, as an occlusion sweeps across southern England and stalls as it pushes up against colder air further north. The probability of snow might have been even higher if it happened during the night, but from the look of it this will be enough to close the Woodhead and Snake pass.
It’s certainly a complicated looking cyclonic picture on Sunday as an elongated trough develops, and stretches out across central England. Two separate low centres form, one of them continues eastward into Northern Germany the other slides south to merge with another developing low that’s heading for Brittany (fig 1). These two combine and between them form an intense low that tracks eastward across northern France (fig 2). This low has gale force northeasterly on its northwestern flank that pull down cold air from further north, this looks likely to be of snow especially over higher ground, and could be heavy, this combined with this very strong gradient could produce blizzard like conditions for a time across the southwest and south Midlands.
The solution for Monday from the GFS model is supported by the latest T+84 forecast chart from the Met Office (fig 3). Obviously the track is very critical, but the potential is there for a lot of snow, especially if the low is reluctant to move away, and very reminiscent of the Christmas Day snowstorm of 1927.
Listening to the BBC forecasters (something I do only rarely these days) I notice that there is a lot of model uncertainty regarding the exact track that the secondary low circulating around the remains of storm Caroline will take on Sunday, although the latest 06 UTC run of the GFS now seems to be taking it slightly further north across Northern England that the previous 00 UTC run did (fig 1).
Not only that, but developments on Monday look fraught with possibilities that have only just come to light in the latest run (or was I busy doing something else). That looks a bit like explosive cyclogenesis that takes a low 0f 955 hPa into Brittany by 06 UTC on Monday morning (fig 2). It looks very reminiscent of the Boxing day storm of 1999 that caused so much damage in France.
This was from the 06 UTC run of the GFS (fig 2), just 6 hours later the solution was entirely different in the 12 UTC run (fig 3). All that I can say is that the various NWP models are in a state of high anxiety at the moment, and the possibility is that anything could happen over the next few days.