The British Isles just had it’s coldest start to March since records started in 1878, but will severe winter weather in the British Isles occur more often now?…
In this country, it’s very common to experience a cluster of mild winters (2013-2017), followed by a cluster of cold ones (2008-2013). Of course there are exceptions to the rule, and we are not saying we’re about to enter a cluster of colder winters for the next few years, but it’s very possible. This would mean that over the next few winters (2018-2022), we experience much more in the way of cold, snow and severe winter weather (for our country anyway).
The Solar Cycle
There’s an interesting connection between low solar activity and an increased chance of northern blocking. Northern blocking cells are areas of high pressure that cut off the flow of normal westerly (mild bearing) winds into the UK, northern blocking occurs occasionally but needs very specific atmospheric conditions to develop. A sudden stratospheric warming is one of them. Low solar activity, is thought to be another “aid”, in setting up this specific atmospheric balance that allows northern blocking to develop, draining air from the poles and pushing it into the country. Generally speaking, it is thought that lower solar activity leads to an increased chance of cold winter weather.
We are heading towards a grand solar minimum in the coming few years:
The level of cold we recently experiences was absolutely exceptional. Air as cold as that we just experienced, in the lower troposphere was the coldest since 1991 and the most widespread levels of cold (-16C in Scotland and England at 5,000ft), since 1987.
In a typical cold spell temperatures are close to freezing, which means some areas of the atmosphere are above freezing, this allows snowflakes to become “wet”, stick together etc, therefore visibility during snow showers is much higher during “typical”, wet and cold UK cold snaps. Snowfall rates of 5cm/hour may produce visibility of 0.8km, moderate snow, however during very cold spells which happen once every 5 years or so (like the one we just encountered), snowfall of 5cm/hour may produce visibility of less than 0.1km, especially combined with strong winds.
The wrong kind of snow occurred in February 1991 and crippled British Rail.
What caused the recent beast?
Between the 3rd and 10th of February 2018 a major stratospheric warming and polar vortex split occurred. The stratosphere (the upper levels of the atmosphere), experienced a temperature increase of about 40C in just a few days.
4th February 2018:
10th February 2018:
The polar vortex strength determines the strength of westerly winds in this country, generally speaking. A stronger polar vortex in the stratosphere most of the time correlates to a text book strong jet stream over the country, with bouts of wind and rain affecting us.
Obviously a weak, split polar vortex means the opposite, the large rise in temperature at 10hpa, around 150,000ft, down welled into the lower regions of the atmosphere (troposphere), and this caused a great big area of high pressure to form.
The result was easterly winds, air originating from the pole and travelling over brutally cold Siberian land. When such cold air passes over the North Sea, a relatively warm 8C with temperatures at 5,000ft of -16C, the result is huge cumulonimbus clouds and heavy consistent precipitation. Some parts of eastern England and Scotland saw 2ft aggregate of snow and drifts into 10ft. More exposed highland areas such as Nenthead (Cumbria), experienced snow drifts of 20ft.
Unusually, snow drifts were also recorded in urban areas. Snow drifts in suburban Leeds, Sheffield, Manchester, Newcastle, Edinburgh, Glasgow, London and Birmingham, Cardiff and Hull were recorded; this kind of weather (snow drifts to lower levels), only occurs once every 5-10 years, recently, but in the 60s, 70s and 80s occurred a few times a decade.
The fact this cold spell was short lived suggests that some of these background signals, such as solar activity, are still unfavorable for cold. The severe winters during the last solar minimum occurred towards the end of the minimum phase. We are now just about entering the start of the solar minimum phase – a big difference. As ever, a thaw kicks in.
A truly remarkable experience. But will it happen again? Nature’s balancing act is sure to come into play – we’ve experienced some of the mildest, stormiest spells of weather for many years, consecutively. The chance of a consecutive spell of colder, snowier winter weather for the UK is “increased”, especially given the upcoming grand (maunder) solar minimum between 2019 and 2021: