John gives us his latest thoughts on likely weather trends over the next few weeks. To ensure you are reading the very latest weekly blog, check out our Wow and Why page here
*UPDATE IN BOLD BELOW – Increased chance of disruptive snowfall later this weekend for some
As expected, the end of Autumn was ushered in by a wintry few days, with northerly winds bringing hard frosts and, for some of us, the first snow. However, the cold block of weather has loosened its grip. This will be enough to allow an encroachment of milder Atlantic air to break through as we head into the new week.
Some readers, (perhaps with a penchant for cold and snow), have asked me if my ideas on a chilly run-up to Christmas have therefore changed.
No they haven’t. Whilst this milder influx had not been anticipated a few days ago, there are good reasons to believe that it is temporary. The atmospheric waves that circle the northern hemisphere are again showing signs of becoming more contorted and larger in the next couple of weeks. And larger waves tend to slow down or even go into reverse. This will be reflected in terms of weather. We may not be looking to the west for long…
MONDAY 4TH DECEMBER – SUNDAY 10TH DECEMBER
‘Dry and mild’ to ‘cold and wintry’ via ‘wet and windy’
The weak begins on a quiet and mild note. Most places will be dry, if rather cloudy. Where cloud-breaks do occur, it will feel quite pleasant. However with light winds across southern parts of the UK, lingering patchy fog, and maybe a touch of overnight frost, are possible.
By midweek, however, there are signs of change. Details of timing are elusive at this range but there is an emerging signal. As arctic air once again confronts the mild ‘interloper’, a deepening area of low pressure will develop between the two. The energetic battle between mild and cold above our heads will manifest itself in some potentially very wet and windy weather for a time.
Slowly but surely through the latter part of the week, the cold looks like winning out. In the process, the rain may well turn to snow – initially in the north. But by the weekend, the arctic air will have flooded south across all of the UK, bringing a return to low temperatures, sharp frosts and wintry showers. But at least the sun will reappear!
*There is now an increasing chance that a low pressure system from the northwest will slide across parts of the UK later in the weekend, bringing the chance of more prolonged and potentially disruptive snowfall. Areas to the north and east of the low pressure centre are most prone. Further south and west milder air may bring rain for a time.
The track of this system will be unclear for several days yet, but will be crucial in terms of rain and snow distribution.
MONDAY 11TH DECEMBER – SUNDAY 17TH DECEMBER
*The low pressure mentioned above will sink away southwards, allowing colder air to flood back across all parts of the UK
It’s beginning to feel a lot like Christmas (… and the weather helps)
In previous blogs I’ve talked about the role that the stratosphere may play in affecting our weather as we head further into winter. There’s much research into how the top and bottom of the ‘weather-sphere’ interact. For example, it’s known that strong stratospheric winds can help to energise our jet stream to propel waves of mild westerly winds across us. This so called ‘Stratospheric Polar Vortex’, far from being a harbinger of deadly cold, is actually quite the opposite. The stronger it is, the milder we tend to be.
However, there are no signs of it strengthening much at present. Indeed, computer models are indicating that in the next couple of weeks, the Polar Vortex may, if anything, weaken further.
…there are no signs yet of extreme cold
This leads me to suspect that through the week, changes at ground level will be slow. Our atmospheric waves will be fairly stuck in position. The UK and western Europe will, most likely, be sitting in a cold ‘trough’, dominated by northerly winds as we head towards mid-month. With low pressure over or just to the east of us it will often be cloudy and breezy with wintry showers. By ‘wintry’, I mean a mixture of rain, sleet and snow. But frosts are likely when skies clear.
Further weather fronts may attempt to push milder air in from the west. Indeed, as we’ve seen in the last week, they may make some inroads. But they probably won’t succeed for long.
At this stage, there are no signs yet of extreme cold.
MONDAY 18TH DECEMBER – SUNDAY 31ST DECEMBER
Very different from last year
By Christmas time last year, with temperatures in the mid-teens, daffodils and snowdrops were in bloom across the nation. That’s a measure of how remarkably springlike it felt in the depth of our so-called Winter.
The atmospherics this December look very different, and there is little to suggest any significant change to the rather chilly prognosis. The Polar Vortex looks set to remain quite weak. So too does the ability of the rather sluggish jet stream below it to bring waves of much milder weather to us for very long.
As for snow on Christmas Day? I mentioned last week that it’s statistically very rare, but I still think it’s probably a little more likely this year than most.
As I mentioned earlier, there are no clear indications of severe cold weather coming. However, scientists will be keeping a very close eye on the stratosphere. There’s a small chance that the Polar Vortex could stall completely, even go into reverse in the next few weeks. This would be as a result of what’s termed a ‘Sudden Stratospheric Warming’. Then things really would be turned upside down. We’d be looking very firmly to the east for our weather by January.
But that’s for another blog…