Tag Archives: Will it be a white Christmas

Dreaming of a white Christmas?

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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All bets off for white or green Christmas

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

The GFS countdown to Christmas Day

xmas2412
The op chart for Christmas Day on 24/12 shows the UK split between influence from a low to the north of Scotland and a European high giving a balmy SW’ly . Rain moves up from the SW during the day. Temps in London rising to 13C after a low of 4C. Best chance of anything wintry northern Scotland

The odds for snow on Christmas Day have been shortened for those that live in northern Scotland, reflecting the latest operational model runs that suggest the current mild regime will continue in the south.

 

The operational runs of the weather model GFS began to include Christmas Day in its forecast on December 9. Admittedly T+384 is la-la land in terms of trying to accurately predict what the weather will be like on the day but I thought it would be fun to see how the outcome changes over the next two weeks or so.

William Hill odds for snow on Christmas Day:
9th: London 5/1; Aberdeen 5/2; Edinburgh 3/1; Glasgow 3/1; Newcastle 4/1; Belfast 5/1;  Birmingham 6/1; Norwich Airport 7/1; Penzance 10/1
10th: unchanged. 11th: unchanged. 12th: unchanged. 13th: unchanged. 14th: unchanged. 15th: unchanged. 16th: London 8/1; Aberdeen 7/2; Edinburgh 4/1; Glasgow 4/1; Newcastle 5/1; Belfast 5/1;  Birmingham 7/1; Norwich Airport 10/1; Penzance 16/1.

22nd: London 12/1; Aberdeen 5/2; Edinburgh 7/2; Glasgow 7/4; Newcastle 5/1; Belfast 10/3;  Birmingham 10/1; Norwich Airport 10/1; Penzance 12/1.

23rd: London 18/1; Aberdeen 5/2; Edinburgh 7/2; Glasgow 7/4; Newcastle 5/1; Belfast 10/3;  Birmingham 10/1; Norwich Airport 10/1; Penzance 16/1.

My predicted outcome for London made at the beginning of December:  TMax: 7C  TMin: 1C Moderate westerly 60% chance of rain shower 1hr of sunshine

  • Please note that the outcome will change markedly from run to run, day to day. The best hint of what the weather will be like will be from T=240z (10 days) and, reliably, T+120z. If the pattern is zonal then detail can only start being pinned down at T+72z.|
xmas091206z
5C, variable winds with threat of rain approaching from south-west. Chance of wintry showers Liverpool northwards. Snow On Christmas Day 5/2 Aberdeen Airport 3/1 Edinburgh Airport 3/1 Glasgow Airport 4/1 Newcastle Airport 5/1 Belfast Int. Airport 5/1 Leeds Bradford Airport 5/1 Liverpool Airport 5/1 London Heathrow 6/1 Birmingham Airport 6/1 Dublin Airport 6/1 Manchester Airport 7/1 Bristol Airport 7/1 Cardiff Airport 7/1 Norwich Airport 10/1 Penzance RNAS Culdrose
xmas1012
The operational chart for Christmas Day on 10/12 shows ridging from the south allowing a brief spell of quiet weather. Temps in London a couple of degrees above freezing with frost at night. A flurry possible almost anywhere though east coast most likely.
xmas1112500mb
The op chart for Christmas Day on 11/12 shows a ridge bringing a brief spell of cold, quiet weather. Temps in London about 6C after a cold, possibly frosty start. Dry to start though increased risk of rain from the west later. Best chance for anything sleety probably Glasgow…
xmas1212
The op chart for Christmas Day on 12/12 shows the UK in a col. Rain a possibility almost anywhere but chiefly in the SW and south. Temps in London about 6C and a low of 3C. Best chance for anything wintry probably Aberdeen toward midnight…
xmas1312
The op chart for Christmas Day on 13/12 shows the UK in a returning N’ly regime. Heavy rain spreading in to SW and S. Temps in London about 12C and a low of 6C. Best chance for anything wintry in the far north
xmas1412
The op chart for Christmas Day on 14/12 shows the UK in a returning N’ly regime. Starting dry in the SE but rain spreading in later. Temps in London peaking at 13C after a low of 10C. Best chance for anything wintry in the far north
xmas1512
The op chart for Christmas Day on 15/12 shows the UK split between a returning N’ly regime and a large area of high pressure centred over Switzerland, advecting warm air from North Africa. Mostly dry across the UK with best chance of precipitation NW Scotland. Temps in London peaking at 10C after a low of 7C. No chance of anything wintry, anywhere
xmas1612
The op chart for Christmas Day on 16/12 shows the UK split between a returning N’ly regime and a large area of high pressure over central Europe, advecting warm air from North Africa. A band of rain lies across the UK though dry in the SE. Temps in London peaking at 13C after a low of 11C. No chance of anything wintry, anywhere
xmas1712
The op chart for Christmas Day on 17/12 shows most of the UK in a balmy SW’ly regime, controlled by a strong high pressure over central Europe. Air over the SE is all the way from the Sahara. Any precipitation confined to Scotland. Temps in London peaking at 11C after a low of 8C. No chance of anything wintry, anywhere
xmas1812
The op chart for Christmas Day on 18/12 shows the UK split between influence from a low centred over Iceland and a European high giving a balmy SW’ly . Air over the SE is from northern Spain. A band of rain heralds cooler air from the NW. Temps in London peaking at 11C and falling away during the day. Best chance of anything wintry Western Isles of Scotland
xmas1912
The op chart for Christmas Day on 19/12 shows the UK split between low centred off north of Scotland introducing a cooler NW’ly airstream while south just about hangs on to the European high. A band of rain clears SE early on 25th from the NW. Temps in London peaking at 10C and falling away during the day. Best chance of anything wintry high ground in N England and northern Scotland
xmas2012
The op chart for Christmas Day on 20/12 shows the UK split between influence from a low to the north of Scotland and and a European high giving a balmy SW’ly . Rain moves in from the west during the day. Temps in London rising to 12 after a low of 4C. Best chance of anything wintry northern Scotland
xmas2112
The op chart for Christmas Day on 21/12 shows the UK split between influence from a low to the north of Scotland and and a European high giving a balmy SW’ly . Rain moves in from the west during the day. Temps in London rising to 12 after a low of 4C. Best chance of anything wintry northern Scotland
xmas2212
The op chart for Christmas Day on 22/12 shows the UK split between influence from a low to the north of Scotland and a European high giving a balmy SW’ly . Rain moves up from the SW during the day. Temps in London rising to 13C after a low of 4C. Best chance of anything wintry northern Scotland
xmas2212
The op chart for Christmas Day on 22/12 shows the UK split between influence from a low to the north of Scotland and a European high giving a balmy SW’ly . Rain moves up from the SW during the day. Temps in London rising to 13C after a low of 4C. Best chance of anything wintry northern Scotland
xmas2312
The op chart for Christmas Day on 23/12 shows the UK split between influence from a low to the north of Scotland and a European high giving a balmy SW’ly . Rain moves up from the SW during the day. Temps in London rising to 13C after a low of 4C. Best chance of anything wintry northern Scotland

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Will it be a white or green Christmas Day?

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

Shoulder of Mutton lake, Wanstead PArk
Shoulder of Mutton pond, 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 8-1, slightly longer than I’d expect at this time of year. With high pressure building and a general cooling trend this week I’d expect those odds to start to come down.

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. Frustratingly, 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 12 of the last 33 Christmas days.

Tree damage by the war memorial in Wanstead High Street by Scott Whitehead
The period just before Christmas last year was very stormy

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.

xmas day 2014I 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 69 times or 40%. I then had a look at the years that most closely follow this October and November. None of the years saw a white Christmas, however it is interesting to note that five out of the six years saw some snow during the month. Snow often falls before and after Christmas. Why that is no-one knows.

So my guess for the weather on Christmas Day this year is for a maximum temperature of 6C after an overnight low of around 0C. With a little rain likely I suppose there is a chance of at least something sleety falling though I’d be surprised if, on Christmas Day morning, we pull back the curtains on a wintry Dickensian scene.

* 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.