From The Old Farmer's Almanac
In the fall, it seems that almost any warm day is
referred to by most people as "Indian summer."
And, while their error is certainly not of the world-
shaking variety, they are, for the most part, in error.
Here are criteria for an Indian summer:
As well as being warm, the atmosphere during Indian
summer is hazy or smoky, there is no wind, the
barometer is standing high, and the nights are clear
and chilly.
A moving, cool, shallow polar air mass is converting
into a deep, warm, stagnant anticyclone (high pressure)
system, which has the effect of causing the haze and
large swing in temperature between day and night.
The time of occurrence is important: The warm days
must follow a spell of cold weather or a good hard frost.
The conditions described above must occur between
St. Martin's Day (November 11) and November 20.
For over 200 years, The Old Farmer's Almanac has
adhered to the saying, "If All Saints' (November 1)
brings out winter, St. Martin's brings out Indian summer."
In the fall, it seems that almost any warm day is
referred to by most people as "Indian summer."
And, while their error is certainly not of the world-
shaking variety, they are, for the most part, in error.
Here are criteria for an Indian summer:
As well as being warm, the atmosphere during Indian
summer is hazy or smoky, there is no wind, the
barometer is standing high, and the nights are clear
and chilly.
A moving, cool, shallow polar air mass is converting
into a deep, warm, stagnant anticyclone (high pressure)
system, which has the effect of causing the haze and
large swing in temperature between day and night.
The time of occurrence is important: The warm days
must follow a spell of cold weather or a good hard frost.
The conditions described above must occur between
St. Martin's Day (November 11) and November 20.
For over 200 years, The Old Farmer's Almanac has
adhered to the saying, "If All Saints' (November 1)
brings out winter, St. Martin's brings out Indian summer."
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