During the late winter and spring on 1998, a widespread outbreak of persistent forest fires caused by an El Nino- related drought resulted in the burning of more than 5000 km2 of forests in southern Mexico and Central America. The smoldering nature of the fires, lack of rainfall and poor vertical dispersion resulted in a massive pall of smoke. General circulation patterns resulted in frequent periods of smoke transport into the southern United States, especially northwards through Texas into the southern Plains. The frequent smoke intrusions, which occasionally reached as far northern as western Ontario, persistent from 8 April through 7 June 1998. At times aerosol concentrations (PM10) reached levels sufficient to warrant public health warnings. Coincident with the smoky episodes was a sudden and unexpected increase in the percentage of lightning cloud-to-ground (CG) lightning flashes having positive polarity (+CG) as detected by the U.S. National Lightning Detection Network (NLDN). In the southern Plains (Texas, eastern Colorado, New Mexico, Oklahoma, Kansas and Nebraska) over a two month period the percentage of flashes having positive polarity jumped to three times the long term climatological normal. Some storm systems covering multiple states produced +CG percentages of 50-70%, an unprecedented event. Analysis of the NLDN data reveals the more numerous +CG flashes also had peak currents substantially higher (85%) than average. Positive CGs are the trigger for mesospheric transient luminous events (sprites) believed to be a regionally important source of NO in the upper atmosphere. Thunderstorms forming in the smoky air masses were observed producing a record number of spites. Such a large-scale perturbation in the electrical properties of storms is totally unexpected. Whether fires in other regions produced similar alterations in storms is under active investigation.