What has caused the particularly cold weather that has blanketed the UK in snow this year? How can you get an idea, as early as September, whether to get your skis out and sharpen your crampons for a top winter or not? And how does this tie in with climate change? David Dobson has the answers, and we also round up a selection of the best photos of mountain days in the British snow.
Please note: all photos were taken before lockdown or in accordance with the current stay-local guidelines.
As early as September this year, David Dobson, a geologist and winter mountaineer with a keen interest in weather science, was gearing up for a cold, snowy, British winter. How did he know? In this article, David answers a few questions, including: what are the early clues that it is going to be a good winter and how does a cold snap tie in with climate change?
DD: Winter mountaineers can spend more time watching weather forecasts than getting out into that weather. How many times have snowfalls in early December risen hopes of a glorious winter season, which were then dashed by a January thaw? Maybe we are all looking in the wrong place – maybe the answer lies in the equatorial Pacific. And, just maybe, we can get some indication of how our winter might turn out as early as September.
Snowdon's Crib y Ddysgl doing a fine impression of an epic alpine ridge a few weeks ago. Photo: Eilir Davies-Hughes
The first thing to say is that weather and climate are two related but different things. Weather forecasting is all about understanding how the local or regional details of the weather system will interact from day to day to create weather patterns in the short-term. Nowadays, organisations like the Met Office are pretty good at that day-to-week-long forecasting.
At the other end of the scale, climate modelling looks at the average behaviour of the planet over much longer timescales of decades or centuries. If something happens which is not included in the prediction – say we double our CO2 emissions – then the climate predictions won’t get it right, but if we input the right assumptions then these days we can get pretty good predictions of how the climate will respond.
Unfortunately, the timescale for planning a winter holiday falls into the gap between the two camps of weather and climate forecasting. It is much harder to predict what will happen in this grey area. So how can you get a feel for how the coming winter might turn out, as early as September?
In December 2020, Greg Boswell, Hamish Frost and Graham McGrath put up a new route in Glencoe: False Penance, IX,10 **
It is all to do with where our weather comes from. The Earth’s rotation causes weather systems to drift eastwards on average. This means that, to get a feel for the future weather, you have to look to your west. You can, for example, often see next week’s UK weather in the Atlantic.
What’s more, there is a link between the Chilean Pacific coast and the winter weather we can expect in Europe. ENSO (El Niño Southern Oscillation) is a cycle related to the development of hot water bodies which accumulate on the Chilean Pacific coast and can persist for several years, causing extreme weather events all around the Pacific. El Niño is the warm phase of ENSO and La Niña is the cool phase.
In years when La Niña events occur at any strength in the Eastern Pacific, this forces the weather systems in the North Atlantic to tend towards negative North Atlantic Oscillation Index (NOAI) values. If you have a low NAOI value, it tends to result in a harsh winter in the North Atlantic.
On 8 January, James Kirby cut a heart-shaped ice hole in a Lake District tarn so his girlfriend could enjoy her first open water ice dip. Photo: James Kirby
That is what has happened this winter; a moderate La Niña event developed in September 2020, which persisted to give us our particuarly cold winter.
That is how it happens on average, but in such a complex system as global weather there are always other factors which might come in to play to change things. And, of course, these short- and medium-term oscillations don’t change the long-term trends of global warming, unfortunately.
One of the things which the warming climate does, however, is drive towards more extreme events – the El Niño system has been much more active and stronger since the 1980’s but we have yet to see if stronger La Niñas will develop as well – if so, we might have a hope for occasional hard winters even as global average temperatures rise, but it is too early to say.
So, if you hear about a La Niña event developing in the autumn, you might be in for a decent winter – but don’t blame me if it doesn’t happen!
Keep your finger on the winter pulse
Via the US National Ocean and Atmosphere Administration (NOAA) website. They are currently predicting that the la Niña will last until spring, which might mean good conditions for the rest of this winter season, for those who can make it to snowy places.
Parsley Fern Gully on Snowdon looking remarkably Alpine earlier this month goatskisandboards ; skier: johncrookguiding.com
Also WATCH One of Those Days (Snowdonia Style):
A nice little film by goatskisandboards
About the author
David Dobson is Professor of Earth Materials at University College London, and he has recently qualified as a summer Mountain Leader to provide his students with more rounded field instruction. He combines these interests in a YouTube channel, OneMinuteGeology , (OMG) offering short, accessible, videos of interesting geology features that you might see while out walking or climbing. Look out for him emptying his rucksack in the next issue of Summit magazine. You can also follow him on Instagram .
References/resources:
Impacts of two types of La Niña on the NAO during boreal winter , Zhang, W., Wang, L., Xiang, B. et al, Clim Dyn 44, 1351–1366 (2015)
ENSO and Global Seasonal Climate Updates , World Meteorological Organisation
North Atlantic Winter SLP Anomalies Based on the Autumn ENSO State , D. Pozo-Vázquez, S. R. Gámiz-Fortis, J. Tovar-Pescador, M. J. Esteban-Parra and Y. Castro-DÍez, Journal of Climate, 18, 97-103
Scottish snow cover dependence on the North Atlantic Oscillation index , M Spencer and R Essery, Hydrology Research (2016) 47 (3): 619–629
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