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Lightning flashes that go from one cloud to another average about a quarter of a second in duration. Less common cloud-to-ground lightning flashes can last more than a full second. Or so we thought. Hi I'm Dave Thurlow and this is the Weather Notebook.

Scientists are now finding a new class of lightning flashes thousands of times faster than those previously observed. National Center for Atmospheric Research scientist Eric Defer has found that flashes within a cloud can play out as quickly as 23 millionths of a second, and perhaps even faster than that.

Out of about 5,400 flashes observed in a July 10, 1996 storm in Colorado, only 83 were cloud-to-ground. More than 800 intracloud flashes had durations of less than one thousandth of a second. Many of these lasted no more than 23 microseconds, which was the measuring instrument's sharpest resolution.

the short-duration lightning tends to occur at heights of 4 to 7 miles within the storm, in close proximity to the strongest updrafts and the most intense precipitation. Thus, according to Defer, the ultraquick flashes might someday serve as a real-time tool for judging a storm's severity. If this turns out to be the case, severe weather forecasts will truly be lightning fast.

The weather Notebook is a production of the mount Washington Observatory. Underwritng is provided by Subaru, and major support comes from the National Science Foundation.