On the Horizon – Brace yourselves!

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

This winter continues to confound some of our most expert meteorologists. Why the head-scratching? Well, there is some well-established received wisdom on how ocean and atmospheric patterns around the globe ‘should’ affect the jet stream . These ‘known factors’, combined with output from powerful long-range computer forecasts would have had us believe that mild, moist and mobile Atlantic winds would be dominating our weather by this stage in the season. ‘Daffs’ up and temperatures in the teens as February approaches?

It isn’t quite working out that way. It’s true that a burst of strength from the jet stream is about to sweep all before it. But as we’re about to see, the strong westerlies it delivers will be far from mild. Not only that – this Atlantic invasion, like its predecessors, may again be brief. 

The wintry weather (and a flurry of hype) will make the headlines


Wild and wintry

I have already heard a good deal of hype about the week to come, describing a cold spell of “epic proportions”. This is nonsense. But after a quieter spell, the days ahead will certainly wake us from our slumbers.

Mid-month arrives with a bluster, to say the least. At speeds of over 200mph, the jet stream will surge across the Atlantic from Canada into the heart of Europe – dividing warm air on one side from cold air on the other. Once wet weather has cleared through on Monday, we will most definitely be on the cold side of things.

Travelling very quickly over the sea, the Arctic air we are hit with won’t be as frigid as it was when it left Newfoundland, but it won’t have warmed up much either! Temperatures will fall away quickly through the early part of the week, with showers turning increasingly to sleet and snow from the north.

It’s the high ground of northwest Britain – where the wintry squalls will be quite incessant – that I am most concerned about. Feet of snow could fall on the mountains, with much larger drifts, thanks to the strong winds. However I also expect some large conurbations of Scotland, Northern Ireland and northwestern parts of England and Wales to be affected by some disruptive snow showers at times. The wintry weather (and a flurry of hype) will make the headlines.

Further south and east, there will actually be plenty of sunshine, but even here some wintry showers are expected. Nobody is immune from a dusting of snow and overnight frost will be widespread.

With such a strong jet stream on our doorstep, there is always the chance that it will spin up an area of more prolonged rain, sleet or snow as we head towards midweek. The computer models will struggle with this potential until much nearer the time. And the track of such systems will determine who gets what. However, snow will always be more likely to the north and rain to the south.

For those hoping for just a brief cold snap, there’s not particularly good news on the horizon for the end of the week. There are the first signs of the jet stream developing a large and important kink in mid-Atlantic. In the process, those westerly winds will begin to turn into northerlies.

So by the weekend I expect frosts to be quite hard, especially over snow cover. But although there will still be some wintry showers, plenty of fine and crisp weather is expected.



Cold start – Milder later?

Not for the first time, the atmosphere looks to be edging into a ‘blocked’ pattern that the computer forecast models really hadn’t envisaged a few days earlier. Cold air will be established across the UK, with a contorted jet stream struggling to remove it.

The majority of model output suggests that the jet stream will reinvigorate, sweeping the block away, and introducing milder westerly winds as the week progresses. However, given the evidence of the last few weeks, I am not at all surprised to see from the latest output that this outcome is now far from unanimous.

My hunch is for another ‘battleground’ setting up in the vicinity of the UK. Fronts from the west will slowly and erratically try to dislodge the cold block to the east. In the process, we can expect a messy mix of rain and some snow, with temperatures slow to recover.



Unreliable evidence

Current model output is ambiguous and, given the evidence of the winter so far, utterly unreliable. But I expect any wetter, windier spell to prove temporary, enabling longer drier spells to develop.

One reason for the drier trend lies in the stratosphere, where winds will start to slow as the month changes. This is something which is not unusual at this time of year, and tends to help weaken the jet stream. This can enable blocks of higher pressure to gain more of a foothold.

At this time of year, murmurings can be heard from experts and non-experts alike about the potential for a Sudden Stratospheric Warming. This irregular occurrence can send the whole atmosphere into reverse, and can usher in prolonged and severely cold easterly winds.

There are now hints of this happening, although it must be stressed that most winters it doesn’t happen at all. But we’ll be watching for telltale signs at the top of the atmosphere. They may be crucial to how the rest of winter turns out.