October marks the establishment of diminishing daytime length, sharp winds and cooler temperatures. It is during this time where Mother Nature's effortless pace towards the winter season becomes a focused matter for herself. Despite the persistent stride towards a winter wonderland theme, Mother Nature provides an anticipated and annual event for the residents of the Mount Washington Valley. Featured during October, the Indian Summer supplies a short-lived break from normal weather conditions, which allows the residents to experience a taste of summer for one last occasion.
Believe it or not, the Indian Summer commonly occurs during the latter half of September through most of October. In fact, the period of warmth is even known to take place during November and December. A prime example for an Indian Summer is when the Mount Washington Valley receives a several day stretch of warm afternoon temperatures into the 70s. Common attributes to the period of weather also include mostly clear skies, nearly stationary wind, and little, if any, precipitation. The first hard freeze of autumn typically occurs prior to the event. Nevertheless, the criterion for an Indian Summer ranges greatly from region to region.
You may wonder what air mass produces the several day stretch of warm weather conditions during autumn. Extending broad into our atmosphere, a very large high-pressure system forms across the Eastern United States. The system halts the airflow of the Polar Jet Stream, which therefore pushes and locks cold air into Canada. The high-pressure system remains nearly stationary for approximately five to fourteen days. The Indian Summer air mass is also known to produce fog during nightfall. Known as subsidence inversion, air sinks and forms an inversion layer above the surface of the earth. Clouds then cease to form as fog appears after nightfall.
The coincidental frequency of the harvest moon and the period of warmth produce both mystery and excitement for many. Some often wonder why the period of autumn weather is known as Indian Summer. Story has it that local Indians believed that the warmth was attributed to the good graces of their god. When the tribes described their belief to European settlers, the event became commonly referred to as the "Indian's Summer". Upon the contrary, many also believe the name originated on the Indian Ocean in 1770 as mariners received calm and fair weather during autumn.
The mystery will always be marveled as to whether or not the Indian Summer originated with mariners or Indians. One standard that will always become accurate is the annual likelihood of receiving a final taste of summer during autumn. It is for this reason why residents of the Mount Washington Valley are able to relive a summer's day before the reality of winter settles upon the region.