Winter's on its way
Winter looks set to come early to the UK with very cold air expected to sweep southwards across most areas by the end of the week and into next weekend.
By Saturday, the air will be unusually cold for November and with still relatively warm seas, all the ingredients are there for some heavy falls of snow, even at low levels.
The dark blue line shown on the chart below gives an indication of the thickness, and hence coldness of the air. It is rare to see air any colder than this at our latitude at this time of the year.
The mechanism for heavy snow will be through a process called 'potential instability'.
As deep cold air flows across the warmer sea it forces the warmer air in contact with the sea aloft. The warmer air cools quickly as it rises, condensing into clouds. The precipitation then falls back through the deep cold air, turning quickly to snow.
The activity of the showers that form is directly proportional to the contrast in temperature between the sea surface and the mass of air flowing south, and it is in these very situations that not only is heavy snow produced, but thunder is sometimes reported too, such is the energy of the cumulonimbus clouds which develop.
As ever the devil will be in the detail and will be crucially dependent on the direction of the wind. At the moment eastern coastal counties look most prone to disruption, although it is likely that other areas could be affected too with troughs of low pressure bringing snow showers inland.
Timing of any disruption is unclear at this stage, as the air will get colder slowly from Wednesday onwards. At first snow is likely over hills, but towards the end of the week and into the weekend some snow is likely at all levels.
Most models are suggesting that the atmosphere will become slow moving and blocked with a very cold East or Northeasterly set up likely through much of next week .
Interestingly, early spells of intense cold so early in the season are not a reliable indicator of what the rest of winter may bring.
The old Yorkshire saying 'Ice in November to bear a duck, the rest of winter nowt but slush and muck' has proved to be one of the more reliable of the 'old wives tales' over the years.
Hello, I’m Paul Hudson, weather presenter and climate correspondent for Ö÷²¥´óÐã Look North in Yorkshire and Lincolnshire. I've been interested in the weather and climate for as long as I can remember, and worked as a forecaster with the Met Office for more than ten years locally and at the international unit before joining the Ö÷²¥´óÐã in October 2007. Here I divide my time between forecasting and reporting on stories about climate change and its implications for people's everyday lives.
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