Why is there so little lightening with tropical systems when there is so much rain? I didn't hear a single clap of thunder but recorded 3.75 inches of rain in Eastern Wake County.

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Bill Switzer

MIKE MOSS SAYS:       Bill,      While the airmass associated with tropical cyclones is quite unstable (rapid decrease in temperature with height), that instability is most concentrated in the lower atmosphere (around 15,000 feet and below), while mid-upper levels of the atmosphere tend to have lower vertical temperature lapse rates, along with temperatures that tend to be warmer than those typical at the same altitudes outside of the tropical cyclone. The warmer temperatures tend to result in higher freezing levels, and the lower lapse rates at the altitudes where mixed (liquid and frozen) hydrometeors exist tend to minimize the charge separation processes that act more efficiently in typical thunderstorms. This doesn't completely eliminate the possibility of lightning (I heard a few rumbles of thunder during Hanna's approach, and noted some sporadic activity on lightning detection maps as well when I arrived at work) but it does tend to limit the number of discharges compared to what one might expect with all those bands of showers and "storms" rotating across the area. Sounds like you were on the eastern edges of the really high rainfall amounts. I had about 4.2 inches of rain at my house, a few miles north of Holly Springs and east of Cary, while a wide corridor of 5-7 inch totals ran north-south just off to our west.



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