Weather Whys; Indian Summer Origins

This is weather-wise, Indian summer is a well-known phrase in American weather law. It refers to a period of unseasonably warm weather that occurs in October or November after the first frost of autumn. Many regions of the United States experience such a warm spell, but it's the Ohio Valley and mid-Atlantic states that most often feel its effects. The origin of the phrase is uncertain, but it apparently was first used in the 19th century. Some historians believe it came about because the period of warmer weather gave American Indian tribes extra time to prepare for winter. For the east coast and Ohio Valley, Indian summer occurs when a large dome of high barometric pressure sits over the eastern United States. That high is often centered above West Virginia, and so it's known as the West Virginia high. The air in that system is calm and stable, and at first it makes for clear warm days. But the nights remain cool since the clear skies and stable conditions allow a lot of

the earth's heat to escape into space. But before long, Indian summer often shows its dangerous side. The dome of stable air traps smoke, dust, and other pollutants near the surface. And if the high pressure stays in the same area for several days, the air can become very hazy. It may even contain enough pollutants to create a health hazard, especially to people with respiratory or heart problems. So like many weather phenomena, Indian summer has both good and bad points. It can be enjoyable for a few days, but if it stays around too long, increasingly hazy skies may suggest it's been too much of a good thing. Whether wise is produced with the assistance of the National Weather Service Forecast Office and the National Severe Storms Laboratory, both in Norman, Oklahoma, and is made possible through a grant from the National Science Foundation. I'm Drew Barlow.