I’ve put together a few top 10s of stats for Wanstead, St James’s Park and Heathrow for the month of March.
The month, the first of the meteorological spring can offer really contrasting weather; perishing cold and very pleasant warmth are both very possible, as the values show.
Probably most notable in the list is the cold March of 1962 which was the coldest of the 20th century and 11th coldest in a local list going back to 1797. March 2013 was also very cold. Strong winds from deep depressions often feature as does the odd blizzard.
Marches in the 1960s also appear to often start very cold and end very warm; the term ‘In like a lion, out like a lamb’ being very appropriate.
Models suggest that the first half of this March, in stark similarity to 1962, will continue February’s cold theme with further hard frosts and occasional snow.
•Though this blog only covers extremes back to 1959, thanks to Met Office digitised data, I’ve unearthed records prior to this. Both W.A.L Marshall’s A Century of London Weather (covering 1841 to 1941) and J. H. Brazell’s London Weather (covering 1841 to 1964) confirm the coldest March day as the 13th in 1845 when 25F (-3.9C) was recorded at Greenwich.
The coldest March minimum was 4/5 in 1909 with 9F (-12.8C) at Epsom. Greenwich and Hampstead recorded 14F (-10C)
This week has the potential to see new temperature records set or matched as very cold air moves in off the continent.
Whilst amounts and location of snow are very difficult to estimate at more than 24hrs to 48hrs away there is no doubt that the incoming air is very cold indeed.
In the early hours of Wednesday one weather model is showing extremely cold air (496-504 DAM ie very low thickness) just off the coast of Scotland. In the last 60 years there have been only three occasions where air approaching this thickness (500 DAM and lower) has been recorded in the UK:
February 1st 1956: Hemsby, Norfolk
February 7th 1969 at Stornoway, Outer Hebrides January 12th 1987 at Hemsby.
With the deep cold air in place the potential for snowfall comes once the air starts to become unstable. East London, and much of the east coast, best falls come where convergence lines ‘streamers’ form.
If persistent, these ‘Christmas tree’ features are capable of producing snowfall accumulating at the rate of 5–7cm per hour in especially cold
outbreaks, albeit often very locally. The steep thermal contrast between the very cold air and the current warm anomaly in the North Sea could make any snowfall very heavy indeed.
Streamers during the cold spell of January 1987 saw 30cm fall widely with some up to 65cm in Kent and 45cm in south Essex. Parts of Cornwall saw up to 40cm.
During a cold spell in February 2009 thundersnow was recorded – the favoured spot this time being parts of Surrey which saw 30cm.
Personally the most snow I have recorded during a cold spell was in February 1991. A very deep cold pool, not unlike what is forecast this week, covered much of the south. in air approaching 500 DAM. Days and days of snow followed dumping knee-deep powder in my local park in suburban East London. Reported depths included 20cm at St James’ Park in the centre of London, and 38cm at Rettendon, Essex.
There is a very good paper on cold pools and snowfall here.
With met models now coming into reliable range it now looks odds on that very cold air from the continent will be in place across most of the UK from early next week.
The big question is how long will the cold last and how much snow will fall? While the latter looks likely at some point once the air is in place it is impossible to pinpoint where and how much any given place will receive at this range.
In terms of longevity latest data shows the spell could have real staying power though my experience with models over the years has shown that they can overcook the potential of a cold spell.
I’ve lost count of the number of times when excited enthusiasts proclaim that an incoming cold spell is going to last as least three weeks; the reality being that the intensity of the cold has gone after four or five days. Cold spells since 2008 often arrive as a ‘blob of cold air’ from the continent that eventually gets ‘warmed out’; it’s been a very long time since we had a cold spell that’s been fuelled by a continual feed of air off the continent.
To illustrate my point I had a look back at every cold spell in this area of suburban east London since 1960. I weeded out the feeble efforts of the last few years by only considering spells where the maximum didn’t exceed 2.8C. The results spanned from the most recent cold spell of March 2013 to the mammoth 31-day Siberian blast that began on Boxing Day 1962.
In another blog I remarked how similar the recent pattern was to February 1962. This cold spell began on the 26th and lasted 9 days. Some 7cm of snow fell, this drifting in the wind, possibly making it seem worse with only 4 hours of sunshine which would have maintained any snow cover.
One of the snowiest cold spells happened in February 2009, eight days after an SSW event that lead to a polar vortex split. This four day spell saw a total of 26cm of snow fall.
The last week or so has been agony for model watching coldies wishing for a snowy end to winter.
Solutions have often flip-flopped between a mild and cold outlook. Even this morning at 6 days out the GFS and ECM model temperature outcomes differed by some 20C, a choice between spring and deepest winter!
Sometimes you have to try and second guess what is going to happen by looking at previous patterns from years past.
Yesterday at Philip Eden‘s funeral I spoke to Woodford Green resident Ron Button. He pointed out how much this February reminded him of February 1962, a month that was non-descript for the first three weeks before turning very cold and snowy. Ron, who has kept a meticulous record of the weather ever since his interest was prompted by the severe winter of 1947, produced diaries of 1962 when he was living in Stratford. The entry for 26th / 27th read: “4 inches of snow with drifting”!
The March that followed was the coldest of the 20th century, ranking 10th in my list back to 1797, and 0.3C colder than March 2013. The fact that the monthly sunshine in 1962 was only slightly below average is testament to how cold the source of the air must have been. March 2013 was very dull by comparison!
An entry in London-weather.eu reads that March was colder than any of the previous 3 winter months: “The first three weeks were mostly mild and dry. It was often breezy which resulted in fewer than average night frosts. Frontal systems off the Atlantic passed through the London area, most of them weak though on the 12th, nearly 8mm of rain fell with southwesterly winds gusting to 57 knots. During the last week of the month, it became much colder, and on the 26th snow fell with the temperature not rising above -0.3C all day.”
The sensor unit, 750m NNE of the weather station wansteadweather.co.uk on the Aldersbrook estate, is much better exposed and will hopefully offer more accurate wind and sunshine readings. It will also provide a chance to further investigate the area’s microclimate.
The station has already shown that the golf course is warmer on a radiative cooling night than the Aldersbrook Estate.
There’s been much anticipation regarding the forthcoming sudden stratospheric warming (SSW) event with many hoping that a resultant split vortex will result in unseasonably cold weather in the UK and… copious snow in the low-lying south-east.
An SSW event, which reverses winds high up in the atmosphere from a westerly to easterly, can downwell into the troposphere, bringing weather from a (usually) cold continent instead of the warm Atlantic.
While a split PV event is usually more conducive for cold weather in the UK, as opposed to a ‘displaced vortex’, which usually favours only the eastern US, it is by no means a guarantee of a cold pattern subsequently evolving.
Looking 45 days either side of the central date for vortex splits gave the following, chaotic graph.
But every year is different. And there appears to be more likelihood of an SSW making a difference, in terms of prompting a colder pattern, the earlier in the winter it occurs.
The SSW in 1985 was followed by a 45-day mean temperature anomaly of -3.8C! If you look at a shorter timescale, 15 days after a split PV and the anomaly is -10C on January 16th: -4.9C is the second coldest January day in Wanstead of the past 60 years.
At the other end of the scale the SSW event on March 23rd 1965 was followed by a POSITIVE anomaly of 3.4C. Perhaps solar influence this late in the year can override any SSW? Elsewhere, however, according to the website london-weather.eu: “3rd March – A combination of deep snow cover and clear skies allowed minimum temperatures to fall below -21C in northern Scotland.”
During another SSW in 2001 results in London were fairly unremarkable though heavy snow fell in Ireland.
The other result to consider is the influence from ENSO. It seems that when La Nina is ‘too negative’ this can ‘overcook’ proceedings and actually leave our part of the UK with a positive anomaly, as this table shows. It should be noted, however, that thicker Arctic ice in the 1960s would also possibly have had more influence than now.
There hasn’t been a full SSW event for years. The impact this one will have on our weather in London, a tiny part of the globe, is impossible to quantify. Though the latest model output is encouraging for anyone looking for a chilly end to winter.
The cold spell of February 1991 saw unusually deep snowfall in central London. The 20cm recorded at St James’s Park on the 8th was the greatest cover recorded at the site since the severe winter of 1962/63.
Courtesy of the Met Office
My own memory of the event was that the synoptics evolved fairly quickly. I was away at university at the time and had to be back for a family event that weekend. After seeing a forecast predicting that a foot of snow was on the way I jumped on a train a day earlier than planned and returned to London. The following morning all hell had broken loose as deep snow paralysed public transport.
Snow fell on the following 6 days with no thawing as the temperature remained below zero until the 10th. The maximum of the 7th was -3C. By the 9th there was widely 20cm of level powdery snow lying. Getting around was difficult – I remember some drifts during walks into town were thigh high.
January 2017 was a wet month. Just over 64mm of rain was recorded, 121 per cent of average, slightly less than last January.
The monthly mean finished 6.4C, 1.2C above average and the mildest January for four years.
Some 44 hours of sunshine were recorded, 88 per cent of average, the dullest January for six years.
The most notable event was during the early hours of the 18th when the ‘storm with no name’ felled many mature trees across a swathe of England, including a large beech on Blake Hall Road that led to the closure of the road during morning rush hour.
I’ve put together a few top 10s of stats for Wanstead, St James’s Park and Heathrow for the month of February.
Probably most notable is the cold February of 1991 which saw the deepest snowfall I can remember – days of snow saw the level depth past my knee in suburban London. February 1986 was also very cold but also very dry with little snow.
Februaries in the 1990s were also often warm with 19.7C being reached in Wanstead on 13th in 1998. I wonder when we will see the first >20C recorded?
It is a shame that the Met Office only publishes easy to access daily data in Excel format back to 1959 as this obviously omits the classic snowy February of 1947 which is worth a blog on its own.
My winter forecast for the London area can be found here.