EMAIL EXCLUSIVE: John Hammond’s Month Ahead 12 Degrees and Drizzle – Merry Christmas?!
The dismal darkness of recent days is enough to test the seasonal cheer in the best of us, isn’t it? So we’ve cheated and come to Austria to find blue skies and snow! Not for a holiday, I hasten to add. Sara and I are out here filming. All very festive it is too! Meanwhile, back home, there’s no shortage of events to get you in the Christmas spirit, of course. There may be tinsel, choirs and mulled wine to lift the mood, but Jack Frost isn’t exactly nipping at your nose, is he? And if you believed the bullish predictions of some computer-generated long-range forecasts in recent days, then you’d have written off a White Christmas already.
Top tip: Don’t trust them. The atmosphere is on a knife-edge as the Big Day approaches.
Opposing forces in the atmosphere
Several ‘battles’ between mild and cold
Increasing chance of snow later in period
MONDAY 3RD DECEMBER – SUNDAY 9TH DECEMBER
Just one crisp day – too much to ask?
After a weekend of mild and mucky weather for most, there are signs of an interruption to this seemingly relentless conveyor belt of wind and rain. A larger kink in the jet stream will briefly block our Atlantic winds, allowing chillier air from the Arctic to creep in for a time, especially to northernmost parts of the UK. Here, a welcome return of drier and crisper weather is on the cards, with the prospect of sunshine by day and frost by night.
At present this chillier interlude looks very temporary for some. Before we have time to take a breath, more rain clouds will be appearing on the southwestern horizon. But how far north will this milder air get? The first of several ‘battles’ this month may be about to be joined. While the south will see rain, as the wet weather spills into the colder air further north, there’s the chance of snow. The higher ground of Scotland and Northern Ireland will be most prone, but it’s one to watch. It’ll be a midweek of stark contrasts north to south.
“That’s nice and vague, John”, I hear you say.
For every battle there’s a winner and a loser, and this battle will profoundly determine the nature of the weather through the second half of the week. The trouble is that subtle ripples in the jet stream many thousands of miles away right now look set to magnify the scope for errors in UK forecasts next week. By the weekend, we could be affected by chilly Arctic air with widespread night frosts or a return of mild and damp weather from the sub-tropics. As I sit here now, only a fool will give you a definite answer to that quandry.
“That’s nice and vague, John”, I hear you say. Yep – I apologise. But in this game, sometimes precision is delusional, even just a few days away.
MONDAY 10TH DECEMBER – SUNDAY 16TH DECEMBER
Irresistible force v Immovable object
As we approach mid-month, it doesn’t get any easier! The big picture reveals the stark potential for dramatic and impactful shifts in weather type. A reservoir of cold Arctic air will be building to our northeast. At the same time, another burst of jet stream energy will be hurtling milder air towards us from the Atlantic. The bulk of evidence would suggest the balance of power returning towards the latter for a time. But we can expect fun and games where the two meet!
…in truth, there’s lots of pressure – and that’s just from my friends and relatives!
Southwestern parts of the UK look set to see the mildest, wettest and windiest weather. Further northeast, it’s much less clear cut. But once more, Scotland is most likely to hold onto the coldest air for longest, with the greatest potential for frost and/or snow.
And this picture describes the dilemma of forecasting this December’s weather. With two impressive and opposing forces setting up, I expect big swings and big errors in medium-range computer forecasts. The stakes are particularly high because the potential for impactful weather of various types is large.
MONDAY 17TH DECEMBER – SUNDAY 30TH DECEMBER
The pressure rises
It’s not just the second half of December we’re talking about here, John – IT’S CHRISTMAS! No pressure, then! Well, in truth, there’s lots of pressure – and that’s just from my friends and relatives!
Statistically, this is one of the most energetic periods of the year for westerly winds – from the ground all the way up to the top of the stratosphere. So there’s no real surprise, perhaps, that many computer models are indicating that a strong jet stream will continue to supply spells of mild, wet and windy weather across the Atlantic.
Forecasting snow in this part of the world is far too easy!
There are, however, indications that at the top of the atmosphere, far from strengthening, the polar vortex will weaken through late December and into the New Year…
There is also the likelihood that lower down the atmosphere, waves of tropical energy that circle the planet will also start to interfere with our westerlies.
So with this in mind, there is potential for the jet stream to weaken or at least be deflected from its path. This would allow high-pressure frigid air from the north and east to back up against the ‘tide’, and provide a more sustained block to milder air.
So – enough waffle! I expect a greater dominance of colder weather through this period. Mild and wet conditions are more likely to be restricted to southwestern areas. The dividing line is impossible to call, but will be crucial in terms of snowfall. However, so far, I’m reasonably happy with the emphasis of our Early Winter Forecast here which covers the period December-January.
I’ll be leaving the Alps soon, and I’m pleased. Forecasting snow in this part of the world is far too easy!