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Thunderstorms and Lightning
Rain and Flooding

How does a thunderstorm start?


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July 02, 2009 11:06AM

Thunderstorms start usually along a frontal boundary usually assoicated with a cold front but sometimes can happen with the other types of fronts. Along a cold frontal boundary, warm moist air is lifted up and over the cold air mass sitting behind the front. The warm moist air being uplifted along the frontal boundary cools by expansion and the moisture is condensed into clouds. Now here is where the fun part begins, the warm moist air that was uplifted along the cold frontal boundary is uplifted by updraft winds that continue expansional cooling and condensation upwards vertically. Usually before you see the thunderstorm mature you will start to see fair weather cumulus clump together into whats called cumulus congestus. Cumulus congestus are mash potato shaped heaps of cumulus clouds that are coming together and are getting shot upwards in vertical motion by updraft winds. When a thunderstorm reaches maturity, it reaches the upper troposphere and the top of the thunderstorm cloud is ripped apart by the upper level jetstream into anvil cirrus clouds which are then carried downstream of the storm by the upper level jetstream. Before a thunderstorm matures, downdraft winds form in the front of the storm carrying precipitation and sometimes downbursts out of the storm. Once a thunderstorm runs out of moisture and energy, it starts to dissipate and weaken and eventually dies out all together.