Tag Archives: Will it be a white Christmas in London?

Weather

Dreaming of a white Christmas?

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I’m not. And it is not because a glimpse at the latest GFS operational run at T+324z (on the 12th) reveals that many could be sitting down to their festive lunch in mild Atlantic air, with possible frontal rain bringing a miserable afternoon with heavy rain in the evening.

Cold spells in early to mid December often end around the 20th, a momentary change to a more mobile regime. Even the cold winter of 1962/63 saw this mid-December warm up with the snow not arriving until Boxing Day.

I will be keeping a daily eye on the GFS and adding to this blog to watch the daily twists and turns, adding to this blog from here.

Just over 24hrs away now on Sunday 24th and the weather tomorrow is again looking mild,in London, about 11C and breezy at lunchtime with rain spreading in very late evening. Best chance of any flakes over the high ground of Scotland.

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On Saturday 23rd, just 54hrs away now, and the GFS op run is again showing the same change to cooler air albeit slightly delayed to previous runs. Temps in London about 10C / 11C, breezy – any rain not arriving to well into the evening. Best chance of any UK snow is Glasgow, into the evening as the cold front clears – and obviously flakes on high ground in the north.

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On Friday 22nd, less than 90hrs away, the GFS is again showing the UK on the cusp of a change. Conditions in London look very mild 11C – 13C before dropping back to 5C after a spell of rain in the evening. Best chance of any snow over the highest points of Scotland.

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Down to 108hrs to lunchtime on the 25th and the situation still shows the weather regime on the cusp of change with the anticyclone over France pulling away south. High temps in London about 9C or 10C with rain late in the evening. Snow risk across the Highlands as colder air digs in. Screen Shot 2017-12-21 at 08.35.34

On Wedesday 20th, the synoptic situation on 25th looks on the cusp of a big change to something more unsettled as the high pulls well south of its current position. A heavy band of rain is approaching from the west though it would be well into the evening before it affects London. Best chance of any snowfall if you fancy a flutter is Glasgow.

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On Tuesday 19th, Christmas lunchtime appears to be the transition day from the present high pressure dominated weather to something cyclonic. In London a dry, cool and cloudy start will be quickly replaced by a spell of rain that clears eastwards. Max 11C, min 3C as the front clears. Best chance of snow looks west coast of Scotland and Pennines.Screen Shot 2017-12-19 at 08.28.58

A week from today and Christmas day will have already dawned. The GFS 00z op presents an unsettled outlook with a transition from mild to cold; London looks warmest at 9am before a cold front sweeps SE’wards. Best chance of anything wintry falling: west coast of Scotlands and Pennines. Over the last couple of years the pattern has already been locked in to mild but this year’s constant ups and downs suggests the weather type  it is all still to play for. Screen Shot 2017-12-18 at 08.13.28

On Sunday 17th, the weather is looking less settled than yesterday with a weak high pressure much further south over the Pyrenees. A cool NW’ly regime with upper air around -5C, allowing any precipitation to be wintry. A chance of snow west coast of Scotland, Pennines and north-west Wales.

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On Saturday 16th, weather on the 25th is under the influence of high pressure centred over Brittany. Quiet weather with a high of 6C or 7C after an overnight frost. There appears little chance of anything wintry falling as the source of the upper air is all the way from the Azores.

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On Friday 15th, Christmas day lunchtime again looks like a day in between a relatively settled mild pattern and a cold, unsettled regime with potential for slider lows after Boxing Day. The 25th itself again looks chilly and nondescript. A high of 6C or 7C, light winds and potential for some rain later. Things are in a state of flux so I’d expect detail to change again tomorrow.

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On Thursday 14th, midday on 25th is looking fairly non-descript. High pressure sits over the near continent with a declining ridge up to Scotland; the UK sits in a battleground with cold air over the near continent and mild air trying to push in from the Atlantic – most of the UK is just on the chilly side. The best chance of any snow is the east coast of Scotland. Still all to play for but it was this date over the past couple of years that the models started to get a good handle on Christmas day proceedings.Screen Shot 2017-12-14 at 14.35.19

Screen Shot 2017-12-13 at 09.52.12On Wednesday 13th I notice that the Daily Star reckon we are ‘odds on’ for a white Christmas, yet I can’t find a bookie anywhere to ‘lay’ these odds; at 12 days out there’s no way any model could be ‘odds on’.

This morning’s (12th) 00Z operational run of the GFS has London at 10C with a chance of rain. Best chance of any white stuff probably Aberdeen.

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Christmas, Christmas Day weather, Weather

All bets off for white or green Christmas

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Weather models are now in range of predicting the weather on Christmas Day and the all important question of ‘Will it be a white one?’

xmas-morning
High pressure centred over the near continent leaves the UK in a feed of very mild air from the Azores

The operational output from the GFS model today answers that question with a resounding ‘no’. A huge anticyclone centred over the continent puts the UK in a very mild SWly feed, the air source from the Azores. You would expect temperatures in London to top around 12C after an overnight low of around 5C.

The Daily Star this morning was even more bullish with it’s splash proclaiming that punters had poured money into Yuletide being exceptionally mild, predicting 15C which would give last year’s record warm period a run for its money. But they have based this forecast on one operational outcome on one model!

Anyone who follows weather forecasts knows that there’s always huge uncertainty in outcomes beyond five days. So putting faith in this forecast 16 days before the event could be dismissed as plain stupid. A closer look at the ensembles – model solutions that pick out trends of several operational runs – suggest that there is very wide spread in outcomes for the weather for Christmas Day: either very cold or very mild! And the GFS system is also hampered by lack of vertical resolution in the stratosphere.

star
Punters are apparently piling money into it Xmas day being 15C – but ensemble forecasts at this range show outcomes from very mild to very cold.

Taking a broader view of what happens in real life over the last few years there always seems to be a pivotal moment around December 17th. The odds always have to favour the mild weather for us though.

Earlier this month in my November review I found that there was a 55% chance of a cold spell at the end of December. My guess at this range is that the run up to Christmas will see us under the influence of high pressure centred over the near continent – a ‘phantom’ cold spell that is cold at the surface but, at 850mb (5,000ft), well above freezing. Christmas day in London will start frosty with the temperature topping out at 5C or 6C. Any proper cold spell with snow will not bite until 29th.

That’s my guess. My advice to anyone who fancies a flutter is to hold on to your money until the 17th. Or place a bet on both.

* The definition of a white Christmas used most widely – notably by the bookies – is for a single snowflake, even if it lands in the midst of heavy rain, to be observed falling in the 24 hours of 25 December at a specified location recognised by the Met Office.

** On average, snow or sleet falls in the UK 5 days in December, compared with 7.6 days in January, 6.8 days in February and 6 days in March. White Christmases were more frequent in the 18th and 19th centuries, even more so before the change of calendar in 1752, which effectively brought Christmas back by 12 days. Climate change has also brought higher average temperatures over land and sea and this generally reduces the chances of a white Christmas.

xmas-day-since-1840

Christmas, Christmas Day weather, Forecast

Will Christmas Day 2015 be white in London?

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Over the next two weeks speculation on Christmas Day weather will inevitably build. Will Christmas be white or green?

Shoulder of Mutton lake, Wanstead PArk

At this range it is impossible to tell from standard meteorological models though from the 15th, 10 days before the big day and when models can start to be relied upon for at least a general trend, the pieces of the weather jigsaw will start to fall into place.

Latest odds offered by bookies William Hill for a single snowflake at London Heathrow are currently 5-1, slightly shorter than I’d expect at this time of year. With the predominance of the European high I’d expect those odds to start to lengthen.

In terms of proper snow falling and settling, there has not been a white Christmas in Wanstead for over 30 years. In 2010, we could still see the Christmas card Victorian snow scene in small patches if our gardens, but these were leftovers of a previous dump, so it doesn’t count. There has been snow on several Boxing Days in Wanstead (1995 and 1996) and in the weeks running up to Christmas, but not on Christmas day itself. The most typical Wanstead Christmas day weather is mild and dry, although it has rained on 13 of the last 34 Christmas days.

Tree damage by the war memorial in Wanstead High Street by Scott Whitehead

In an earlier blog I had a look at what the last 170 or so Christmas Days in London were like weatherwise and found that snow actually falling on the day is extremely rare. Since 1840 there have been just 19 occasions of snow or sleet falling on the capital on Christmas Day which equates to a probability of just under 11%. If you consider that the last ‘white Christmas’ (see note) was in 1996,  then we are well overdue one.

But the weather doesn’t adhere to human created calendars and behave like it should on any given day. But patterns in any given year can sometimes repeat though correctly predicting they will happen is more down to luck. Nevertheless I’ve had another look at my calculations for this winter and see if there is any way I can make a prediction for Christmas Day.

I firstly had a look at Christmas Day stats overall since 1840. The most common group of maxima in the series is 8.1C and above. This occurred 70 times or 40%. I then had a look at the years that most closely follow this October and November. Ten years were on the list – two saw a white Christmas: 1938 and 1968. Snow often falls before and after Christmas.

xmas 2015So my guess for the weather on Christmas Day this year is for a maximum temperature of 7C after an overnight low of around 1C. With a 60% chance of rain in a stiff westerly wind there is a chance of something sleety falling.

But the fact that 20 per cent of the years in the above series saw a ‘white’ Christmas suggests that, unlike last year which I called right, there is at least *some* chance of snow falling. If you insist on having a flutter, however, Liverpool airport at 5-1 looks most generous.

Going on past form it is possible that Christmas Day will be the ‘changeover’ day for something a bit more wintry as we head into the new year – but it looks like the north Midlands northwards will be the main beneficiary of any of the white stuff

* The definition of a white Christmas used most widely – notably by the bookies – is for a single snowflake, even if it lands in the midst of heavy rain, to be observed falling in the 24 hours of 25 December at a specified location recognised by the Met Office.

** On average, snow or sleet falls in the UK 5 days in December, compared with 7.6 days in January, 6.8 days in February and 6 days in March. White Christmases were more frequent in the 18th and 19th centuries, even more so before the change of calendar in 1752, which effectively brought Christmas back by 12 days. Climate change has also brought higher average temperatures over land and sea and this generally reduces the chances of a white Christmas.