It is very hard to be sure whether there is less snowfall now in Britain than in the past because ‘the past’ has been so variable. Britain lies at a latitude roughly the same as Labrador in Canada but enjoys a much milder winter climate due to the influence of the Gulf Stream, which sweeps a current of tropical water north eastwards from the Caribbean to Britain.
Weather depressions form along this, where cold air currents from the vicinity of Greenland and Canada bump into the mild air above the Gulf Stream, and they typically track eastwards across Britain or south of Iceland. A typical British winter is predominantly mild and wet, with overnight slight to moderate frosts from time to time and daytime temperatures well above freezing. But not always.
Anticyclones sometimes form over the Baltic, Greenland or the near Continent and persist for weeks or even months. When this happens, the flow of mild wet air across Britain is blocked and sub-zero air flows in from eastern Europe, Siberia or the high Arctic. When this happens, severe winters follow and global climate change, at least as experienced so far, has not altered this.
The winter of 2008-2009 was cold and snowy in comparison with the run of mild, rainy winters which had preceeded it. In Devon, in the mild south west of England, there was heavy snowfall in January, February and early March, with snow lying for days and periods of near zero temperatures by day. Night time minima reached minus 9 celsius in places in Devon in January ( 16 fahrenheit). It was a gentle reminder of what British weather can do, something of a media sensation but comparatively benign compared to some of the monsters of the past.
The coldest British winter on record (and reliable records go back to the 17 century) was 1683-4, when the Thames froze at London for two months and the ice reached 11 inches in thicknesses.The late 1600s saw a series of severe winters and the period is often referrred to as the ‘Little Ice Age’. Frost Fairs and skating were organised on the frozen Thames and bonfires were lit in braziers on the ice. The mean temperature fell to minus 1.2 degrees celsius over southern England this winter.
1739-40 was another extremely severe winter, unequalled until 1962-3. London had snow on 39 days and there were 2 months of mean temperatures below zero across the Midlands and southern England. The Thames was again frozen for two months and a low of minus 24 celsius (minus 11 fahrenheit) was recorded.Trees split open as they froze in the cold.
In 1794-5 there was again an exceptionally severe winter, with minus 21 celsius ( minus 6 fahrenheit) recorded in London on January 25th. Yet the first part of this winter had been very mild, with plus 14 celsius recorded widely on January 14th! Very severe winters were also recorded in 1813-14 and in 1816. This latter year is often referred to as the ‘year without a summer’. The Thames actually froze in September! A mega-volcanic event, the Tambora explosion in the East Indies disrupted atmospheric flows and blocked sunlight, cooling the planet significantly. Severe frosts in June killed lambs in the fields.
In the last 100 years, two winters stand out for their exceptional severity, 1946-7 and 1962-3. In both winters, the sea froze around the coast. In 1947, from January 22 to March 17 snow fell somewhere in Britain on every day. Several falls exceeded 60cm (2 Feet) and level snow lay to a depth of one and a half metres in places as far apart as north east England and Wales. Drifts of snow exceeded 5 metres in height, roads remained blocked, trains could not run in places and the army and air force had to brought in to drop supplies to towns and villages which were cut off. Over southern England and the Midlands the mean temperature was between 5.5 and 7.0 degrees Celsius below average. The thaw, when it came, brought damaging 90 mph winds and severe flooding.
In 1962-3 the severe cold set in around Christmas and rain moving south turned to snow over Scotland and dumped 30cm on southern England. In late December blizzards created 6 metre drifts on high ground in south west England and south Wales, both supposedly ‘mild’ areas. All over the country, villages were cut off, power supplies cut and farm animals marooned, many to starve to death with the farmers unable to reach them or dig them out of drifts. Again the armed forces had to be mobilized to aid the civil powers. Britain saw repeated blizzards as warm wet air tried to push in and met cold air flowing from Scandinavia. From Boxing Day to mid March, Britain lay under deep snow. It was the coldest winter since 1740. At Braemar, a town in the Scottish Grampian mountains, a low of minus 22.2 celsius was recorded on January 18th 1963.
The problem is that these exceptional winters were often followed by much milder ones and there have been prolonged periods of mild winters before. This is not the first generation to say that winters aren’t as snowy or cold as they used to be. Given Britain’s northerly latitude, icy winters are always a possibility, so long as the world has ice. A phenomenon known as the North Atlantic Oscillation causes the typical north Atlantic pressure centers to reverse in some winters. A ‘Low’ forms over the Azores and high pressure establishes over the Denmark Strait or Scandinavia. Bitter winds sweep over Britain in consequence. Predicting this phenomenon is not possible at present, but meteorologists know it exists and that when it occurs Britain is in for heavy snow and sub-zero temperatures.
The last quite severe ‘snowy’ winter is reckoned to have been 1978-9, but there were several cold winters with snow in the early 1980s. The coldest temperature ever recorded in Britain was as recent as 1995 however! (at Altnahara in Highland Scotland minus 27.2 degrees celsius, (about minus 18 fahrenheit) matching lows recorded at Braemar in 1985 and 1895). Snowy winters are not yet a thing of the past, they are just bafflingly irregular!