"As weather and human activities change with the seasons of the year, so does the incidence, causes and severity of fires. Cold winter weather increases indoor activities and the need for heating, which brings about the peak period of heating structure fires. Daily fire incidence is at its highest in the spring. Spring is characterized by an increase in outside fires and a decrease in fires related to heating. The increase in outside spring fires is in large part due to the increase in tree, grass, and brush fires. Summer fires reflect an increase of incendiary and suspicious fires, fires associated with fireworks and natural fires caused by lightning strikes. These fires are a reflection of the change to warmer weather and the consequent increase in both outside activities and dry natural vegetation. Fire incidence is at its lowest in the fall. In fall, there is a decrease in outside fires, an increase in heating−related structure fires and the peak period of cooking fires. The incidence of vehicle fires is relatively constant throughout the year, as are their causes. The incidence of daily fires increases during and around four holiday periods: Independence Day, Halloween, Thanksgiving, and the winter holiday period that includes Christmas and New Year's. More fires are reported on July 4th than any other day of the year. Brush and outside fires increase substantially due to family outings and the misuse of fireworks. On Halloween, and the night before, incendiary and suspicious structure fires are about 60 percent more frequent than on an average day."
U.S. Fire Administration: http://www.usfa.dhs.gov/