What is Indian Summer?
Freddy Millison, Oak Brook
In the United States, Indian Summer is a period of dry, unseasonably mild weather in late October or November in the central and eastern portions of the country. Indian summer might not occur in some years and, in other years, it may occur more than once. It often persists for several days, or longer. Days have hazy skies and light winds; nights are cool and may bring frost. Daytime hours are pleasant, with low relative humidity and a lack of clouds.
A deep, warm high pressure area usually dominates, characterized by stable air stratification: mild air at the surface and cool air aloft, resulting in little vertical mixing of air. Smoke and dust are concentrated near the ground, accounting for the haziness.