SAFETY & TRAINING NEWS
Scottish Weather Part 2:
Winter Storms
By Alison McLure
The wind swirled the snowflakes like suds in a washing machine around the ridge, some brushing against my cheek gently, while others stung as the biting wind picked up. We crunched steadily up the snow, my poles on my sack, having been exchanged for my ice axe; cold, but reassuring in my hand. What a great feeling watching the mist roll in and out again across the wild winter landscape. Occasional glimpses of the pearly lochans below in the strange surreal light of midwinter. Another world, where your mind wanders through the mysteries of it all.
Reality kicks in – my back feels really itchy in the kidney area. Have I been drinking enough? Surely I'm not allergic to my favourite fleece bottoms! A mild buzzing in my ears and I suddenly realised what it was! We were close to being struck by lightning and my sticking up poles and reassuring ice axe were not helping! As I crouched and put down my rucksack and ice axe, I shouted to my friends to do the same, I cursed myself for not realising earlier. All those years of training and experience in the Met Office and I had forgotten that the mountains in Scotland experience more lightning in the winter than in the summer. The Met Office can pick up lightning flashes and their statistics between 1990 and 1997 show around 4 to 6 days each winter compared to around 1 each summer.
Lightning is a large sudden electrical spark (a flow of electrical charge), which travels between clouds or from a cloud to the ground. It is caused by a build up of electrical charge within a cloud, due to the movement of ice particles up and down within it. Eventually the charge builds up so much that the cloud can't hold it any more and you get a lightning flash…(oh happy memories of school physics and Van der Graaf generators!)
Lightning, along with thunder, is usually associated with warm sunny days where huge clouds build up due to the heat from the ground. However, it can be a different story over the Scottish hills. Air needs to rise quickly to make the clouds that could produce lightning. Heat is one way to make air rise, although it doesn't only take a warm day; it's really to do with the difference between the temperature on the ground and the temperature in the air. Another method for air to rise is when clouds are pushed across the hills by the wind. The technical term for this is “orographic uplift” (nothing to do with wired bras I am assured!). So when you have a cold north to northwest air flow, combined with a (relatively) warm sea, pushing clouds into and over the hills you can see why winter provides good conditions for lightning over Scotland.
So how can you tell if thunderstorms are a possibility in winter over the hills? The key word in the forecast is “showers”, although not all showers will produce lightning. The more vigorous the shower and the bigger the difference between the ground or sea temperature and the air temperature the more likely lightning will be produced. So when the forecast talks about heavy, prolonged and wintry showers there is some chance of lightning.
When you haven't got access to a forecast, you can pick up some hints by looking around. If the clouds are lumpy, cotton wool like and reach reasonably high into the sky and have a smoother, spread out top like an anvil, they are called cumulonimbus and could produce lightning. Also, if the showers are heavy and produce hail, there is a possibility.
So what do you do if all the signs show that there is a chance of lightning? Remember that the chances of being hit are very slim indeed. Lightning will try to take the line of least resistance to the ground, which means hitting the highest point around. Try to reach low ground, away from trees, overhangs, crags and ridges. Having sticks or ice axes pointing up the way is probably not helpful either, although the main risk is having something which connects you to the ground. It is best to stay out in the open and sit on insulating material such as rucksacks and mats with all parts of your body kept off the ground.
The buzzing in my ears and itchy back stopped when I took off my rucksack and put down my ice axe. The clouds parted momentarily to show some classic anvil tops, but there was no sign of any lightning. It would have been too dangerous to carry on without our ice axes, so we waited until the shower passed over and continued up and down the hill without any more signs of lightning.
There is a section on lightning in "Hillwalking" (the official handbook of the Mountain Leader scheme £14.99 available from the MCofS office) Page 154.
This page is also on the MCofS website here
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