Although the general public often refers to warm spells in the fall as "Indian Summer," most occur before the first frost arrives (which, compared to the suburbs, comes weeks later to Manhattan/Central Park). This analysis goes back to 1950 and looks at warm spells that have occurred mostly in October and November (with some beginning in late September). For my purposes I focused on those that were at least four days in length.
Two-thirds of the years since 1950 have had warm spells of four or more days (including the ten of the eleven years between 2010 and 2020). Seventeen years had two or more, with 1953 experiencing four. There have been ten warm spells that lasted ten days or more, the most recent being in the autumn of 2006. The lengthiest was twenty-one days, which has occurred twice, in 1959 and 1984.
MOST ABOVE AVERAGE
There have been thirty-nine warm spells in autumn that averaged ten degrees above average or more (based on daily mean temperature). The five-day heat wave of Sept. 22-26, 1970 was the most above average, +18 degrees, with four of the five days experiencing highs in the 90s.
|LENGTHIEST AUTUMN WARM SPELLS|
|1959||Sept 21-Oct 11||21||81||65||+11|
|1984||Oct 11-31||21||70||57||+ 8|
|1973||Sept 27-Oct 15||19||74||57||+ 6|
|1995||Oct 2-14||13||76||58||+ 7|
|1986||Sept 23-Oct 4||12||79||64||+ 8|
|1994||Oct 30-Nov 9||11||69||52||+ 9|
|1970||Oct 6-15||10||74||60||+ 9|
|WARM SPELLS WITH GREATEST DEPARTURE|
|1950||Oct 29-Nov 2||5||79||58||+17|
|1971||Oct 26-Nov 3||9||72||60||+14|