Naturalist's Almanac

November 11 is St. Martin’s Day, a day devoted to Martin of Tours, a popular fourth century bishop known for his humility, charity, and kindness to beggars. Because November is a time of seasonal change, numerous weather beliefs have become associated with his saint’s day.

Some of these beliefs are cast as proverbs that try to predict the quality of winter from the weather on November 11. Others are merely descriptive of weather that might occur around November 11. Of these, the most reliable is that St. Martin’s Day might bring a period of warmth.

The English call such a warm spell St. Martin’s summer. They also look for a St. Luke’s summer around October 18 and an All Hallows summer around November 1. The English colonists who settled in this country during the 17th century encountered similar warm spells but different weather beliefs.

Some of their new neighbors believed that pleasant fall weather was a gift sent by a benevolent god who lived in the Southwest. The Narragansetts, who lived in what is now Rhode island, called this god Cautantowwit and looked for good weather whenever the wind blew from the Southwest.

By the 18th century, when St. John de Crevecoeur wrote Letters from an American Farmer, Americans were no longer calling spells of warm fall weather by the names of Christian saints but rather by the new name Indian summer.

Indian summer has since been analyzed by meteorologists as a singularity, a weather pattern that tends to occur at the same time of year more frequently than chance alone would indicate. They explain that the warmth of Indian summer is caused by a high pressure system that settles over the Southeast in the fall.

Unlike hurricanes, which are low pressure systems that rotate counterclockwise and blow wet, windy weather up from the Southeast, these fall highs rotate clockwise and blow warm, dry weather up from the Southwest.

Some years the southwestern winds bring several periods of Indian summer in both October and November. Other years they bring none. The English habit of associating a warm spell around November 11 with St. Martin’s Day offers a useful way to anticipate it. But Indian summer, with its suggestion of a benevolent god sending warm fall weather on a southwest wind, actually does a better job of explaining it.

MORE INFORMATION

American Meteorological Society Glossary

The American Meteorological Society offers an official definition of St. Martin's Summer in this online version of their glossary. They include links to their definitions of Indian summer, St. Luke's summer, All-Hallown summer, and Old Wives' summer.

John Singer Sargent's St Martins Summer

This gallery site offers an image of John Singer Sargent's lovely oil painting entitled St Martins Summer. You can click on the image to get a closer view.

Martin of Tours - Wikipedia

The Wikipedia offers several nice graphics plus ample biographical information on Saint Martin of Tours plus a link to the Catholic Encyclopedia, but no mention of St. Martin's summer. If I were a better person I would figure out how to join the Wikipedia crowd and add a paragraph to their entry ....