Thunderstorms and Spanish Plume: What Are They?
ThunderstormsLet’s remind ourselves how thunderstorms develop. They come from cumulonimbus clouds, which are convective clouds. Thunderstorms can occur all year around, and in the winter can bring snow as well as thunder and lightning, an event that has been dubbed thundersnow. However, we most commonly see thunderstorms in the summer months, as this is when there is more heat, and so more energy to create these enormous clouds. A buoyant atmosphere is required to produce a thunderstorm, and a large amount of energy. As the warm air rises it cools and the water condenses forming small droplets of water. If there is enough buoyancy in the air, the updraft of warm air is strong and rapid, and the water vapour will quickly form a cumulonimbus cloud. As the warm air continues to rise, the water droplets combine to create larger droplets which freeze to form ice crystals. As a result of circulating air in the clouds, water freezes on the surface of the droplet or crystal. Eventually the droplets become too heavy to be supported by the updraughts of air and they fall as hail. As hail moves within the cloud it picks up a negative charge by rubbing against smaller positively charged ice crystals. A negative charge forms at the base of the cloud where the hail collects, while the lighter ice crystals remain near the top of the cloud and create a positive charge.
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Spanish PlumeThere is a particular weather situation where lightning may be especially prevalent, so avoiding being outdoors in these conditions is advisable. It is called a Spanish Plume. There are three main ingredients which are typically involved in a Spanish plume event:
- Very warm air pushing north from the Spanish plateau on a southerly airflow. This can happen at almost any time of year, but during the summer months the extra warmth and moisture leads to increased energy available for storm development.
- Cooler air at height advancing from the west, often associated with cold fronts.
- Strong summer sunshine heating air at and near the surface across France and the UK.
If you are caught outside in a thundery situation, here are some guidelines to follow:Don’t…
- Carry on working in your garden, or go outside at all if possible.
- Use plug-in electrical equipment like hair driers, electric toothbrushes, or electric razors during the storm.
- Don’t use land line telephones during the storm. Lightning may strike telephone lines outside.
- Take laundry off the clothes line.
- Work on telephone or power lines, pipelines, or structural steel fabrication.
- Use metal objects like tent poles, ice axes and golf clubs.
- Handle flammable materials in open containers.
- Stay on hilltops, in open spaces, near wire fences, metal clotheslines, exposed sheds, and any electrically conductive elevated objects.
- Stay indoors if you can.
- Stay away from open doors and windows, radiators, metal pipes, and plug-in electrical appliances.
- Get out of the water and off small boats.
- Stay in your car if you are travelling. Cars offer excellent lightning protection.
- Seek shelter in buildings. If no buildings are available, your best protection is a cave, ditch, or under head-high clumps of trees in open forest glades.
- When there is no shelter, avoid the highest object in the area. If only isolated trees are nearby, your best protection is to crouch in the open, keeping twice as far away from isolated trees as the trees are high.
- When you feel the electrical charge — if your hair stands on end or your skin tingles — lightning may be about to strike you. Drop to the ground
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