EMAIL EXCLUSIVE: John Hammond’s Month Ahead – From mild to bitter..?
Snow won’t be falling from the sky through much of the festive period, but then neither will rain. A strong signal is emerging for a dry and benign spell as the year draws to a close. All the more reason why what comes through January may end up being quite a shock…
Quiet end to 2019
Increasing chance of severe cold in January
MONDAY 24TH DECEMBER – SUNDAY 30TH DECEMBER
Cloud, sun, frost, fog… but no snow
While much of the week looks dry, Christmas Eve starts damp and mild across some southwestern parts of the UK. In contrast, further northeast it will be drier and chillier. And this chillier air will provide a frosty start to Christmas Day for a few. A White Christmas of sorts, I suppose!
Changes will be slow and subtle as a large area of high pressure causes the air to stagnate across the UK for a few days. The dry theme is a strong one, but the distribution of cloud, sunshine, frost and fog will be far less straightforward. Fog, in particular, may become quite an issue; and with so many people on the move, impacts may be significant.
Similarly, temperatures will vary hugely. Double figures for many, but much chillier where fog lingers for much of the day – most likely away from the west.
By the end of the week, fronts will be trying to push milder and damper air more bodily across the UK, although the progress of this is uncertain. Chilly air may hold on across some southern and eastern areas until the weekend. But all in all it looks like a quiet spell to get out and enjoy the many events taking place between Christmas and New Year
the chance… is real and ominous
MONDAY 31ST DECEMBER – SUNDAY 6TH JANUARY
High drama about to unfold?
The year ends with waves of energy from the jet stream repeatedly trying to erode away the high pressure sitting across the UK. Each wave looks set to slow down on reaching our western shores. The breaking of these waves may still threaten westernmost areas with rain, but the extent to which this rain spreads more widely across the UK is not clear.
Wherever that air stagnates – closest to the bubble of high pressure – frost and fog may continue to be lingering issues. But the year will probably start on a predominantly benign note as this high pressure system does not contain inherently very cold air.
Meanwhile, however, high drama is unfolding at the top of the atmosphere. A ‘Sudden Stratospheric Warming’ will have probably, by now, succeeded in splitting the Polar Vortex in two.
The resultant reversal in hemispheric winds aloft increases the chances that eventually, at the bottom of the atmosphere, an intensely cold area of high pressure will surge out of the Arctic and sweep frigid easterlies across ‘temperate’ mid-latitudes. But where exactly?
I attended a conference this week in which the point was reiterated that by no means all of these dramatic stratospheric events lead to us in the UK having severe cold. Furthermore the time-lag for this reversal to work its way through the atmosphere is unpredictable.
However, the chance of very cold and potentially snowy weather arriving is real and ominous.
… I expect a clear signal to emerge over the Christmas period
MONDAY 7TH JANUARY – SUNDAY 20TH JANUARY
Severe cold threatens to sweep in
This period could well be the most severe of the winter so far. (Not difficult, I hear you say).
I must re-state that there are no certainties here. Indeed at this range it would be misleading to suggest that conditions will be anything like as severe as the ‘Beast from the East’. Statistically that remains a low probability.
However, I know from personal communications with major forecasting centres that there is increasing concern about the potential for disruptive winter weather as we go further into January.
There remains a significant chance that a ‘non-event’ ensues, and at this point, nobody can give a definitive verdict. But I expect a clear signal to emerge over the Christmas period. So watch this space…
Sara and I hope you have a peaceful and enjoyable Christmas. Time to take a breath – January may well bring some exhausting drama – and not just in the Palace of Westminster!