I recall a magazine article about lightning - It said that a bolt of
lightning can be tens of thousands of volts and thousands of amperes of
current. Convert that to watts.  


If you believe http://www.thecomputerwizard.biz/lightning.htm
Lightning voltage can be up to 300 million volts.
Lightning current averages 30,000 amps, but ranges from 10,000 to
200,000 amps - 100 To 1,000 times as strong as a steel welder.

One of the television weather reporters said lightning can strike the
ground 30 miles from the storm cloud - even where the sun is shining.


Mark WB3CAI