Thunder and Lightning

Some people say that they can tell when a storm is coming.  The air “feels” different, animals quiten down, birds disappear until the storm has passed. 

There are actually several types of thunderstorm, although here in Britain we are most likely to experience one in the warmer months.  In summer months, the earths surface is heated by the sun, and with this warm air rising, and cooler air sinking it creates conditions for a storm.  The 3 more common storms are an Orographic storm, a frontal storm, and an Air mass thunderstorm.


These kind of storms are caused by the lifting of air over a mountain or a hillside.  These storms can be accompanied by large volumes of rainfall.


Frontal storms occur when different air masses meet, ie, when a cold front meets a warm front.  Cold air is denser than warm air, so as a cold front approaches warm air the warm air is lifted, which then creates unstable conditions in the troposphere (the lowest portion of earths atmosphere).  This unstable air can create massive thunderstorms, and can bring a lot of rain.  You can often see one of these storms developing, they appear as big, dark cumulonimbus clouds.  If there is enough cold air this kind of storm can appear day or night, although often a nightime storm can appear far more impressive as the lightning is more visible in the dark sky.


An air mass thunderstorm typically lasts less than an hour, and can be very localised.  It is caused when a large mass of warm, moist air interaacts with even a small pocket of cold air.  When these storms hit you can quickly find yourself drenched one minute, then drying out the next as the sky clears and the sun comes back out.


What sets this kind of storm apart from the others is the rotation in the cloud.  A supercell is usually found in the warm part of a low pressure system, and can be one of the most dangerous types of storm.  It is basically a huge rotating thunderstorm, the area of rotation withhin the storm is called a mesocyclone that can spawn a tornado. The storm itself can rotate when winds at different levels of the atmosphere come from different directions. If the winds are lined up just right, with just enough strength, the storm turns like a top. Air circulations within the storm combined with a strong updraft contribute to tornado formation.

Info from Wikipedia

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