The Christmas storm singularity

One of the best articles written regarding weather forecasting is Philip Eden’s ‘Does the Weather Have a Memory?’

The crux of the article is that certain weather types can repeat at the same time of year with one having a 100 per cent probability!

The Christmas storm singularity occurs in 84 per cent of years.

While 84 per cent certainly doesn’t mean ‘nailed on’, in the current set up of models being evenly spread between settled and stormy it can be safely guessed at this range that there will be unsettled weather around on the 25th. Whether it will affect the whole country remains uncertain.

The last big snorter of a Christmas storm I can remember in London was 2013. The entry for the 23rd into the 24th reads.

“Cloudy and breezy start grew steadily duller with rain just before noon. Rain grew heavier with some really strong gusts into evening culminating at 2am. Cloud at one point was 10kms thick. Three deaths related to weather.”

There was chaos nationwide with flooding and power cuts.

https://www.bbc.co.uk/news/uk-25512391

The average wind run for this station shows the singularity as well as the mid December settled spell we are now seeing.

Fantastical Christmas day snow modelled

It’s that time of year again! With the midnight run of this model bringing the start of the 25th into range the prognosis for the big day is a rare white one – with snow likely almost anywhere.

But 15 days is an eternity in modelling so we can take this with a council depot load of salt.

It’s often not until 10 days out that models will start to get a firm grip on what the weather will be like on Christmas day.

My guess at this range is a quiet one with fog and frost and a high of 6C in London.

Friday, December 10th

24hrs on and, interestingly, the pattern hasn’t completely flipped to something opposite to above…

Saturday, December 11th

The high is more centrally located over the UK with proper cold air from eastern Switzerland eastwards. Cold, calm with frost and fog in London.

Sunday 12th December

Little change though any colder air is even further east. A Eurotrash high with declining air quality.

Monday 13th December

The models are in a state of flux, more so than usual by the looks of it. No change on my thoughts though.

Tuesday 14th December

Another slack flow with any true, cold air well to the east. My guess remains a dull and cold Christmas day after a slight morning frost.

Wednesday 15th December

Within the much more reliable 10-day range now and the GFS is throwing out quite an odd looking chart. It shows a mass of cold air just to our east, the start of a cold spell that takes us up to New Year’s Eve.

Thursday 16th December

My thoughts on Christmas day still remain the same as they were days ago. Cold, calm with a high of 5C. Beyond that GFS is hinting the Atlantic floodgates will open. I suspect it is jumping the gun by a couple of days and we’ll see a couple of cold days, the 27th being notably cold?

Friday 17th December

The GFS having another hiccup overnight. The situation at 0z hours probably 5C and cloudy in London. But it’s a deteriorating situation with 850mb temps plunging from the north – the conditions that could bring being consistent with the title of this blog. But I’d pay little notice to output like this until it is 48-72 hours away.

Saturday 18th December

A classic battleground scenario on the midnight operational. An even spread on ensembles, too. My hunch is that the high pressure will survive long enough for a quiet Christmas day. After that?

Sunday 19th December

GFS wants to bring 11C, outbreaks of rain this morning…

Monday 20th December

Mild with showers in London.

London Winter Forecast 2021/22

This winter is most likely to be on the colder side of average with near normal rainfall.

While the modelled prognosis for the first half of December looks unsettled with an Atlantic influence evolving from the current chilly NW’ly to a mild SW’ly, local analogues of the climate of London suggest the season could be a bit of a rollercoaster with spells of wet, windy and mild weather alternating with dry, calm and cold.

A large factor to consider this winter is the presence of a slight La Nina that is forecast to evolve cooler.  

Given the uncertainties involved with the influence of ENSO I’ve decided to stick with analogues found in local data that stretches back to 1797.

Overall then the probabilities for the next 90 days are.

MeanProbabilityRainfallProbability
Mild (>5.9C)14%Wet (>178mm)19%
Average (5.1C – 5.9C)38%Average (107-177mm)62%
Cold (<5.1C)48%Dry (>107mm)19%

The above table doesn’t reveal a great deal in that extremes can be hidden in a month or season that finishes broadly average. So I decided to look closer at the winters that were revealed in the analogues.

December

The first month, as already mentioned, looks like it will be on the mild side with possibly a notable storm off the Atlantic before things calm down over Christmas – the period between Boxing Day and New Year’s Eve possibly presenting the best chance of any lying snow in this region.

The below graphs are a smoothed representation of the years revealed in the analogues most similar to this autumn.

What is probably most interesting is that the analogues that shared a similar ENSO / La Nina index to this autumn tended to ‘turbo charge’ any yo-yoing in the weather type, be that super-mild or abnormal cold.

December probabilties for maxima:
Mild: 48%
Average: 19%
Cold: 33%

And precipitation.
Wet: 33%
Average: 29%
Dry: 38%

So, the month overall will be mild and slightly dry

January

The first month of 2022 probably represents this region’s best chance of lying snow this winter. A mild start perhaps with a falling off of temperatures in the final third of the month and a cold spell of a week or so. As with December the influence of La Nina could tend to boost the swings in the pattern.

January probabilties for maxima:
Mild: 33%
Average: 10%
Cold: 57%

And precipitation.
Wet: 19%
Average: 43%
Dry: 38%

Greatest chances for January, then, are cold with average precipitation.

February

The second month may see a slight return of the cold spell in January before temperatures recover for a mild and wet spell in the second half.

February probabilities for maxima.
Mild: 33%
Average: 15%
Cold: 52%

And precipitation.
Wet: 38%
Average: 38%
Dry: 24%

The stats suggest on the cold side overall with average to above average rainfall. Perhaps the depth of the cold skewing any very mild second half of the month?


The extremes that no-one can forecast

As well as the very mild winter of 1989/90 the analogues also revealed the very cold winter of 1978/79. There were others but their occurence makes the probability of a repeat at either extreme at less than 10 per cent.

Luke Howard’s aurora sightings

Luke Howard‘s Climate of London volumes provide a plethora of interesting facts and figures about the atmosphere during a time when few reliable records of London weather were made.

Over a period of just over 20 years he mentions the aurora borealis being sighted somewhere in Britain 15 times.

The first, on March 3rd 1807, describes the phenomenon.

The whole hemisphere very red for some time after sunset which we ascribed to the reflection of light from elevated cirri. Our Manchester correspondent, however, states the same phenomenon at the same time as an Aurora Borealis. Additional communications decisive of this point will be acceptable. The phenomenon was repeated on the 21st which with the preceding and following night was windy.

Seven years later, on April 14th 1814, proceedings were described thus.

Aurora Borealis of late years a very unfrequent visitant in these parts appeared last night with no great degree of splendour but with the usual characteristic marks of this phenomenon. About 11pm when my attention was first called to it there was a body of white light in part intercepted by clouds extending at a moderate elevation from the N to the NW with a short broad streamer rising from each extremity. After this it became an arch composed of similar vertical masses of fibrous light which moved along in succession preserving their polarity and curved arrangement. One large streamer in particular went rapidly through nearly the whole length of the arch from W to E. Some of these masses were rather brilliant and one exhibited colours. After some cessation and a repetition of this appearance carried more towards E and W the light settled in the N and grew fainter in which situation at midnight I ceased to observe it 

Further mention is made on 8th February 1817 and later that year, on 26th October, another account.

A little before 8pm I observed from the neighbourhood of Lowestoft, Suffolk, a distinct commencement of Aurora Borealis in the north in white streamers ascending to a considerable elevation which after a minute or two became converted into a still light the latter remaining for an hour or two after was at length obscured by clouds.

And the same year, as shown in the book.

More sightings were recorded on 12th and 17th October 1819 and 14th December of the same year. Also 31st July 1821.

Six years later, on 18th january 1827, an account of the Northern Lights in Epping Forest was noted.

The final case of the aurora of London was made on 25th September 1827.

Further records were noted on 15th September 1828 in Glasgow and 11th December 1830 at Ackworth, Yorkshire

Thoughts on winter

Lots of hype regarding winter at the moment with contradictory model output being released almost daily.

My early take on this is based on the current state of the El Nino Southern Oscillation (ENSO) index which is currently -0.6 and trending more negative (La Nina).

Using analogues from previous events would suggest that the coming winter in the south-east of England will be broadly average in terms of mean temperature and wetter than average.

Looking more closely at each year suggests the following.

Further scrutiny of the local statistics suggest that the mean temperature for November could be lower than average, some 1.7C below average with rainfall around 20 per cent below average.

I should be noted, however, that in the years that were most similar to this September and October (1958, 1961, 1967, 2001, 2005, 2019) the ENSO index was much closer to neutral than it is now. In other words what happens next month could be vastly different to what happened in those years.

Years prior to those mentioned above add intrigue as ENSO statistics are not available.

1802 (cold January 1803), 1849 (severe January 1850 with ice in the Thames) 1862, 1865 (heavy snow southern England 10/11 January) 1874 (notable December storm)

Obviously a lot can change atmospherically in the next few weeks; this is an early take on my usual winter forecast which will be released on December 1st.

Cloudburst at Brettenham, Suffolk

I hadn’t heard of Brettenham before this Suffolk village recorded over 100mm of rain from the convergence line event on the afternoon of Sunday, July 26th.

A former Environment Agency observer recorded 181.3mm in 1hr 40mins (1640-1820).

Notable on its own but even more so given that Wattisham, an official station 7.3km to the south-east, recorded just 2.4mm at the same time.

Whilst intensely isolated events happen, and often go unnoticed if they occur in uninhabited areas, this one seems more severe than what has previously been recorded.

The greatest 24hr rainfall recorded, according to Robin Stirling’s Weather of Britain, was 279mm on July 18th 1955 in Dorset. The rainfall far more widespread than the event on Sunday.

The event in Suffolk was covered by the East Anglian Daily Times. A report that mentions ‘rain falling in sheets and roads turned into rivers’ can be found here.

England’s gloriously rainy omen

What’s the most ridiculous omen for an England win in the European Championship final against Italy on Sunday? After hearing this on the radio this week I decided to try to find one.

Readers of this blog will know my theories of how the weather and big events seem to be tied together. So it is no surprise that I’ve indeed found one.

Last month, I wrote about summer washouts. The one last month that began on the 17th saw 28mm fall, possibly contributing to what was a dull spectacle; England’s 0-0 draw with Scotland at a rain-soaked Wembley.

While putting together the July list of washouts one of only six events since 1959 began on July 19th 1966. Over 20mm of rain fell, coinciding with England’s group game with France. The Three Lions won the tie thanks to a brace from Liverpool’s Roger Hunt. Days earlier they had been panned after a dull 0-0 draw with Uruguay. No-one, apart from Alf Ramsey, fancied our chances. Yet by the end of the month they were world champions.

So, in terms of football singularities, England’s is one title every 55 years? We’ll know by 11pm on Sunday.

Euro 2020, weather and Wimbledon

Four June washouts in london

Compiling a list of sunless, rainy days revealed some interesting spells of wet weather – the most miserable runs of June days in the capital since 1959.

First up was a three-day spell starting on June 25, 1974. Some 34.3mm of rain was recorded.

Next was a three-day spell starting on June 23, 1991. Some 26.3mm of rain was recorded.

Another three-day spell started on June 25, 1997. Some 36.2mm of rain was recorded.

Finally, and most recently, a two-day spell this month that began on June 17th. Some 28mm of rain was recorded.

The above spells all happened around the date of the ‘June monsoon’ singularity which has a probability of 77 per cent. Though the fact that these occurred 47 years, 30 years and 24 years ago shows that these extreme cases happen a lot less than three years in every four the singularity would suggest.

Comparing the current Northern Hemisphere pattern with 1974 suggests that while there’s just as much heat around at 850mb as there was 47 years ago, including an extreme heatwave over some Nordic countries, the air above Greenland appears colder.

Sunless days and washouts

The weather of late has been in stark contrast to the mostly dry, sunny (if a bit chilly) spring many enjoyed. Indeed the first half of June saw more of the same and, locally, was the warmest start to the first meteorological summer month since at least 1959.

My memory of summers years ago was that it was often hot and sunny but I also remember countless days of staring out the window for hours waiting for relentless rain to let up.

Looking back at sunshine stats to 1959 there has been over 4,400 days where no sun was recorded, roughly a one in five chance of a totally cloudy day.

Considering the months where the absence of sun is most noticed, May to October inclusive, the probability decreases to just under one in ten.

To decant these to ‘washout days’ I’ve only included those sunless days that were also ‘wet days’ where 1mm or more of rain was recorded. The probability further decreases to just under one in twenty.

All very interesting but were there more washout days decades ago or is the memory playing tricks?

Looking overall shows an increase since 2013. Out of all the months the most notable change has been August.

Spring in Wanstead Park

Spring in this neck of the woods was really mixed.

A chilly start to March became fairly benign before ending with the warmest March day locally since at least 1959.

April then turned much colder and drier; just 2.4mm of rain fell during the month – the driest April since 2007 and fourth driest in a local rainfall series back to 1797! Sunshine was abundant with over 200 hours. But clear skies at that time of year, with a polar continental airmass, often means air frost. And the ten recorded overnight was far higher than normal.

May saw things warm up slightly but the month still finished a degree colder than average. Some 80mm of rain fell which is over one and a half times what we’d normally expect. The wettest May since 2007 – the month playing catch up on the total absence of April showers that bring the spring flowers! It was a dull month with only 126 hours of sunshine, 69 per cent of average – the dullest since 1990 was third dullest back to 1881.


In terms of flora and fauna the colder weather played havoc with the trees, bud burst coming much later than recent years. As I write this on June 6th some of the later budders like false acacia have only just come into full leaf. The birds, as they normally do, just seem to get on with it raising their young. I’m not sure what the food supply has been like but judging by the amount of healthy juvenile fledglings I’ve seen I would guess that it has been a good season so far?


Here’s the stats.
March 8C (+0.3) 30.9mm (76%) 90.9 hours (84%)24.1C on 30th (a record that had stood since 1965)
April 7.2C (-2.6) 2.4mm (5.5%) 202.6 hours (127%)
10 air frosts in April, much higher than normal
May 12.1 (-1) 80mm (156%) 125.6hours (69%)
Spring 2021: Mean Thermometer: 9.1C (1.1C below average, coldest since 2013, 111th coldest) Rain Cloud with rain: 113mm (84% of average, wettest since 2018, 150th wettest ) Sun Sun with rays: 425.4 hrs (94% of average, dullest for three years. 51st dullest) The average masked extremes.

Meteorology-based musings about east London and beyond

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