On the Horizon – How long will the cold hold?

John gives us his latest thoughts on likely weather trends on the horizon over the next few weeks. To ensure you are reading the very latest weekly blog, check out Wow and Why

It’s proving to be a winter full of twists and turns – many of them unexpected. In my years of forecasting I’ve observed how easy it is to suffer from an over-confidence in the beguilingly precise predictions of computer models. When the real outcome arrives, ‘amnesia’ then sets in about just how wrong those earlier predictions sometimes were. Computer forecasts are, of course, of huge and ever-increasing value, but they are only a guide. Each model has weaknesses as well as strengths. And a weakness of all of them is that they inadequately portray the range of possible paths that the weather may actually take in its evolution.

In previous blogs through December, I had hinted that we could soon be looking to our east; but even by New Year’s Eve, relatively few computer forecasts suggested that the UK would be affected by strong and raw easterly winds within a week!

So I’d urge trepidation about “what happens next”. This winter continues to throw up surprises. 

MONDAY 8TH JANUARY – SUNDAY 14TH JANUARY

East versus west

Despite many of the ‘known’ drivers to our weather (from the stratosphere to the ocean) suggesting that westerly winds should hold sway through the month, we start the week with a cold block of high pressure sending easterlies our way. Compared with some easterlies, the air is not extremely cold, partly because the Continent is not especially frigid or snow-covered. Nevertheless, a bracing few days are likely, with the chill accentuated by the wind. We can expect some hard frosts if, and where, winds fall light and skies remain clear in the north of the UK.

Already, however, Atlantic fronts will be approaching and, by midweek, cloud and some rain will be edging into the UK. Some snow is possible as the fronts encounter the cold air, and this is most likely across some northern and eastern areas.

The progress of these fronts is extremely uncertain. There is a huge array of possibilities, but it looks as though the fronts will have ‘stalled’ somewhere in the vicinity of the UK. We will be in a buffer zone or battleground between the cold block to our east and milder air trying to arrive from the Atlantic. But for a time temperatures will rise a little.

Later in the week, there are indications that high pressure may push the cold air back westwards, with drier, frostier weather.

By the weekend, though, the balance may shift again. With another assault from the west, there’s the likelihood of further wet weather arriving which, in turn, may turn to snow as it comes up against the cold air.

Computer forecasts ‘know’ less than they ‘think’

MONDAY 15TH JANUARY – SUNDAY 21ST JANUARY

Irresistible force versus immovable object?

Stratospheric westerly winds are very strong at present, which is helping to rev up the jet stream. Developments as far away as the tropics also suggest each ‘attack’ from the west will be more successful at eroding the cold block to our east. Indeed, as the week progresses, Atlantic winds may become more dominant for a time, bringing spells of wet and windy weather. And as the jet stream strengthens and dips towards us , it could again bring the possibility of some quite stormy weather to our shores. Some computer forecasts are hinting at this.

However those who interpret each latest model run as the final solution should be mindful that in all likelihood, none of them at this range will actually turn out to be correct. We have to look at subtle trends.

Given what we have seen already, it would be a fool who discounts the possibility of the block holding on for longer.

 

MONDAY 22ND JANUARY – SUNDAY 4TH FEBRUARY

Blocking returns (if it ever went away…)?

Any wetter, windier spell may well prove temporary. There are indications from the latest extended range computer output that stratospheric winds will slow markedly as we reach the end of the month, something which is not unusual at this time of year. This often allows a weakening of the jet stream, enabling blocks of higher pressure to gain more of a foothold.

As February approaches, I expect drier weather to develop. Crucial to the feel of our weather will be the position of the accompanying areas of high pressure and hence the wind direction. Current model output would suggest that high pressure will be centred to our south, ensuring a mild Atlantic influence and perhaps even early signs of spring.

We shall see. Given the winter we’re having, I fully expect the goalposts to move again in the next week or two. Computer forecasts ‘know’ less than they ‘think’.