John Hammond’s month Ahead – UPDATE ! What are the signs for Christmas?

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 Wow and Why

*UPDATE IN BOLD BELOW – Milder interlude more likely next week

Sometimes, forecasting is easier than others. Well this isn’t one of those times. Just as cold air gets established, there’s just enough energy in the jet stream to nudge it away and replace it with a milder spell from the west. Back and forth we go in the balance of power. The atmosphere continues to be on a ‘knife-edge’ – and that’s a problem for all concerned when snow, ice, and stormy weather are in the mix, as we’ve seen in these last few days.

And because of this knife-edge , I’m not surprised that the computer models continue to be fickle and inconsistent as they look through the Christmas period and beyond. Can we trust them?

MONDAY 11TH DECEMBER – SUNDAY 17TH DECEMBER

Cold… Mild… Cold…

Northerly winds will ensure a cold start to the week. A deep depression squeezing close to our southeastern shores, threatens wind, rain and snow to some southern and eastern areas. Again the snow threat is marginal, and most likely if the wet weather edges into the coldest air well-inland.

For the rest of the UK, crisp sunshine, occasional wintry showers and frost are on offer – the latter particularly harsh where there is snow on the ground.

By midweek, that snow will be thawing. The next set of Atlantic weather fronts will bring another interruption to the cold theme.  We can expect a ‘softer’ feel. But rain will be moving eastwards across the UK and winds may again become quite blustery.

Through Thursday and Friday, the westerlies will be once more replaced by northerlies. So, temperatures will fall back towards “frost and wintry showers” territory. I’m not expecting the extent of snow that some will have seen the previous weekend. For many it’s a bright and crisp picture as we head towards the weekend.

We then look again to the western horizon…

… computers are telling us one thing, while experience is telling us something rather different

 

MONDAY 18TH DECEMBER – SUNDAY 24TH DECEMBER

Christmas Countdown – time running out for the cold?

It’s with some trepidation that I tip-toe into this week. I know, I know – the stakes are high as we approach the ‘Big Day’!

In the last few days, computer models have lurched towards a milder signal for the second half of the month. They are ‘trying’ to rev-up the jet stream to feed predominantly westerly winds and rain across us as we approach Christmas. Frankly, I don’t trust them…

As I mentioned in my last blog, the stratospheric winds around the Arctic are sluggish this winter. Indeed, the ‘Polar Vortex’ that circles the North Pole is distinctly ‘off-kilter’ as I write. This is known to contort the jet stream. As well as this, there are also patterns of weather that are emerging in the tropics that, indirectly, can also block the jet stream’s path.

So in essence, the computers are telling us one thing, while experience is telling us something rather different. Talk about mixed messages…!

Fronts will be pushing in from the Atlantic, spreading cloud and some rain across the country. Milder weather than for some time will become established.

But although many computer models would suggest that the westerlies will sustain their warmer influence through until Christmas, I urge caution.

As I sit here, looking at the array of model forecast output, there is no clear theme emerging as yet. Some are quite bullish in their mild westerly message, but an increasing number are showing that this may not last long.

Amidst the bewildering ‘potpourri’ of possibilities, there are already indictions that by the weekend, the jet stream may again ‘buckle’ and take on a different path…

 

MONDAY 25TH DECEMBER – SUNDAY 7TH JANUARY

White v Green… an uneven contest

The record books confirm that childlike dreams are usually shattered when we wake up and open the curtains on Christmas morning. White Christmases are very rare, even in cold winters. And given the uncertainty in the atmosphere at present, I’d be a fool to offer false hope of a winter wonderland.

Nevertheless, I suspect that as Christmas week proceeds, any push of milder air from the west may again prove to be have been temporary. Given the ongoing state of the larger-scale atmosphere, there’s a good chance that before the turn of the year, a colder block will be re-established.

Up to now, our chilly spells have come from the north. But given the ongoing contorted nature of winds all the way up to the stratosphere, it’s only a matter of time before we see a new twist, and easterlies show their hand. If and when that happens, “chilly” will become “bitter”. It’s just a question of time.