The decision to launch or not is governed by a detailed set of rules gained over years of experience. For instance, when winds exceed a certain threshold or clouds hold electric charge that could discharge as lightning, launches are called off, because the risk of catastrophic failure to crew, or cargo, is too high.
In describing why the launch was called off, Mr. Bridenstine said later in remarks on NASA TV that weather officers were concerned that a liftoff might “actually trigger lightning,” because of the excess of electricity in the atmosphere.
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