Monthly distributions of NLDN and GLD360 cloud-to-ground lightning
Monthly flash density maps were prepared, along with monthly maps of the percentage of the average year's lightning. From January through March, results typically show banded structure associated with small numbers of thunderstorms over the southeastern states. Lightning then spreads north and westward until by June, all of the U.S. except the far southwest is experiencing lightning. New England, the northern Rockies, and the Florida peninsula have a small percentage of their lightning activity outside the months of June, July, and August. Arizona and portions of adjacent states have their highest incidence in July and August. Flash densities throughout the continental U.S. drop off quickly in September.
During summer months, NLDN monthly maps are compared with those from the new Vaisala Global Lighting Dataset GLD360. Results show that lightning over all of Mexico, Central America, and the western Caribbean complement and extend the NLDN coverage in very reasonable patterns.