MOUNTAIN WEATHER

AUTHOR | STEVE HOLMES

Understanding mountain weather and reading mountain forecasts are essential skills walkers, climbers, and mountaineers must learn. This skill is necessary to avoid adventures turning into misadventures, weekend missions into epic tales, and simple walks into unfortunate tragedies. Consider planning mountain adventures around the prevailing weather, not the other way around and always be prepared to change or alter your plan should the forecast be incorrect.

Wind – the most significant influence on mountain weather.

Both speed and direction are the first contributing factors I look for when reading a forecast and thus making my plan. Wind speeds above a certain velocity make mountaineering unbearable and contribute to most, if not all, incidents contributing to mountain weather. It is the most prominent and often memorable feature of the UK’s mountains and is associated with changing patterns in high and low air pressure. The strongest winds are experienced with the deepest and most turbulent depressions and consequently happen during winter.

How high is too much?

Wind speeds above 35mph are worth consideration, and nearly all mountain journeys, especially during winter, will be adjusted for speeds above 50mph. I weigh around 67kg, and a 60mph wind will feel powerful and significantly impact my walking gait and stability on paths, never mind exposed ridges and summits. Working in the mountains does mean I head out into the hills during storm-force winds, but careful route planning is essential for a successful and safe day in high winds.

Some critical (wind*) considerations for a day of winter climbing in Scotland are below:

Has it snowed, and what level is the snow cover – if it snowed overnight, the approach could be slow and tiring.
What has been the prevailing wind direction over the previous five days – snow distribution and cross-loading of slopes is a hazard following a change of wind direction.
What aspect is the climb facing – avalanche avoidance!
Who are my climbing partners – are they as fit or lighter than me?
How do I get back down – 95% of incidents happen in the final 5% of your day.
What is the maximum elevation of my day – most forecasts focus on wind speeds at max height; can I climb lower down?
Are there rivers to cross – nobody wants to get wet crossing a river! Strong winds make for unstable people.

This list can be extensive and will cross over into other considerations discussed below. However, sticking to these seven points around wind will help you make good decisions and avoid unwanted eventful days in the mountains.

Precipitation

Hillwalkers and climbers all appreciate a blue sky day, but many of us will experience wet weather in the mountains, especially if we live in Scotland. It is worth noting there is no single forecast accurately displaying every contributing weather influence, especially when it comes to rainfall. Typically mountaineering instructors and mountain guides use a collaboration of predictions to make plans and judge what conditions we might encounter. It is recommended to consider a broader view of precipitation rather than the millimetres expected to fall on a particular summit at a specific time of day, as other influences, such as a slight change in wind direction or speed, can affect the timing and total amount of rainfall.

Mountains situated to the West in the UK typically see more annual rainfall; this is only sometimes the case during winter when the Cairngorm mountain can see significantly more precipitation than Ben Nevis; remember 2010 & 2018 ‘Beast from the East!’. Limiting rain factors include crossing rivers, waterproof clothing quality and how slippery rocky ground might become. It is well-documented how wet the Skye Cuillin Ridge can be. Still, through continuous evaluation of the weather, sound equipment and, crucially, experience, we manage to guide people over technical sections of the ridge in less-than-ideal conditions.

Snow is often easier to tolerate than rain, yet it can be dangerous and should be treated with respect when planning to travel in snow-covered mountains. A history of the season’s snowfall can be found on the Scottish Avalanche Information Service website and should be used at the initial stages of planning alongside wind direction and speed.

Temperature & Sunshine

The UK’s mountains can be subject to impressive temperature changes, much more so than higher mountain ranges worldwide. The significant gradient change is mainly due to the modest height of our mountains and being a small island in the northern hemisphere.

At the time of writing, Cairn Gorm mountain is forecast to be -10 celsius, with the northerly airflow providing a windchill of -18 degrees C. My kit choices will need to reflect this in the form of warmer gloves, heated mitts and a large down belay jacket. Dont forget extra calories and a flask of warm liquid when it is colder to keep the internal fire burning.

The amount of sun on any given slope is primarily influenced by the slope aspect, which is widely variable in the mountains. North-facing and gentle-angle slopes see relatively little sunshine and cooler conditions, which is often reflected by their vegetation, whilst steep south-facing slopes have more sunlight than level ground, especially during winter when the sun is low in the sky. The sun’s warming effect is particularly prevalent during the early spring when caution should be heightened on snow-laden slopes.

Temperature appears to be the most straightforward weather influence for us to deal with in the mountains, but it is also the most complex factor inside the snowpack. I recommend further reading the SAIS website, Avalanche Essentials A Step-by-Step System for Safety and Survival & Staying Alive in Avalanche Terrain by Bruce Tremper, and A Chance in a Million?: Scottish Avalanches by Blyth Wright and Bob Barton.

Recommended forecasts:

Synergy Guides deliver guided climbing and mountaineering on Skye, Ben Nevis and in the mountains of Glencoe. We also offer instructional courses and bespoke adventures for larger groups.

Synergy Guides deliver Winter Mountaineering from our base in Fort William where we teach people how to stay safe in the winter environment. We aim to cover the basics plus climb some classic introductory mountaineering routes on Ben Nevis and in Glencoe.

Already an experienced winter mountaineer? Take your skills a step further and join us for an Intro to Winter Climbing or push your grades on a Performance Winter Climbing course.

About the author

Steve Holmes owns Synergy Guides, he is a fully qualified Mountaineering Instructor and holds the WMCI (MIC) award. He spends most of the spring/summer on Ben Nevis and the Isle of Skye. You can read more about him here.